HK1118643B - Trickle discharge method for battery pack protection - Google Patents

Description

Trickle discharge method for battery pack protection

Technical Field

The present invention relates to a battery charge/discharge circuit and battery pack protection, and more particularly, to a battery charge/discharge circuit capable of performing trickle precharge and/or trickle discharge. The utility of the present invention may be found in a charge/discharge/protection system for use in portable electronic devices, such as laptop computers, PDAs, cell phones, and/or any type of electronic device having a rechargeable battery.

Background

Rechargeable batteries, especially lithium ion batteries, require a trickle pre-charge (recovery charge) from a charge-depleted state to avoid damage to the depleted battery. When the rechargeable battery is exhausted and its battery voltage becomes lower than a threshold voltage V_UVIn this case, direct charging cannot be performed using a large charging current. Instead, a pre-charge mode is required. In the pre-charge mode, a small charging current is used until the battery voltage is charged to be greater than the voltage V_UVIt can then be charged in normal mode, i.e. by a larger charging current. For lithium ion batteries, the threshold voltage of a unit cell is close to 2.4V to 3.0V, depending on the battery type and manufacturer. The precharge current is about 10mA to 100 mA. However, the normal charging current may be several hundred milliamperes to several amperes depending on the battery capacity.

Fig. 1A shows a charging profile 50 for a lithium ion rechargeable battery. When the battery voltage is higher than V_UVThe battery enters a Constant Current (CC) charging mode, with a large constant current used to rapidly charge the battery (the battery voltage also increases as the battery charge increases). When the battery voltage increases to V_OVWhich represents an overvoltage (the normal overvoltage voltage for a lithium ion battery is around 4.2V), the battery enters a Constant Voltage (CV) charging mode. In this mode, the charger is held at a voltage V_OVThe charging current gradually decreases. When the charging current decreases to a predetermined minimum value, for example 50mA, the charging procedure stops. In the CV charging mode, the charger must refine the voltageSurely adjusted to V_OV(error at +/-0.005V). If so, the charging output is greater than V_OVThen overcharging of the battery will occur, which can lead to safety problems for lithium ion batteries.

A conventional circuit 10 implementing pre-charging is shown in fig. 1B. A precharge MOSFET 12 in series with a resistor 14 is used for precharging. At the time of precharging, the charge FET 16 is turned off and the precharge FET 12 is turned on. Thus, the precharge current is approximately determined by the voltage difference between the charger input voltage VPACK + and the total cell voltage Vcell divided by the series resistance 14 Rpre. When an AC adapter (not shown) is present and VPACK + is higher than cell voltage V_cellCharging or precharging will begin based on the initial voltage of each cell. If the voltage in any cell is below the threshold V_UVThe battery pack will enter a pre-charge mode. Otherwise normal charging will begin.

Those skilled in the art will recognize that the circuit 10 in fig. 1B includes a battery monitor IC 20 that includes circuitry to monitor the voltage and current of each Cell (Cell1, Cell2.. Cell4) of the battery pack 22. Such circuitry may include a switching network 24 to sample each cell voltage. To control the operation of the pre-charge MOSFET 12, the conventional circuit 10 includes a comparator 26 that can apply a constant reference voltage 28 (V) through a switch 30_UV) Is compared to the voltage of each cell.

However, one drawback of the circuit shown in FIG. 1B is that an additional MOSFET (i.e., MOSFET 12) and resistor 14 are required, which adds additional cost and increases the area of the PCB. In addition, in such a circuit topology, a lower cell voltage results in a larger precharge current. Also, the precharge current decreases as the cell voltage increases, which means that a longer time is required to complete the precharge.

In addition, the value of resistor 14 is typically fixed, as are the maximum and minimum values of the pre-charge current, and therefore cannot be adjusted to accommodate different battery pack requirements.

Another drawback of this topology is that the battery pack 22 and MOSFETs are easily damaged in abnormal situations, such as the VPACK + terminal being shorted to the VPACK-terminal, or an external charger being applied back to the VPACK + and VPACK-terminals. In this topology, the discharge FET18 is either turned on to allow discharge or turned off to disable discharge. When the discharge FET18 is turned on, if an abnormal condition occurs, a large current flows from the battery pack 22 through the discharge FET18 and the charge FET 16, which in turn destroys the battery pack 22 and/or the MOSFETs.

In addition, when the battery pack 22 is removed from the electronic system, for example, placed in a cradle, the discharge FET18 may be turned off to protect the battery pack 22 from abnormal conditions. However, since discharge FET18 is turned off, battery pack 22 will not immediately power on the electronic system when battery pack 22 is inserted back into the electronic system, thus requiring a mechanical method or electronic circuitry to signal circuit 10 to turn on discharge FET 18. Additional mechanical methods or electronic circuitry would increase the complexity, price and/or size of the circuit 10. In addition, the battery pack may still be easily damaged due to an abnormal condition after being inserted into the electronic system.

The conventional approach for battery pack protection is to turn off the discharge FET18 to avoid large currents generated when abnormal conditions occur. After being turned off for a predetermined time, for example, 30 seconds, the discharge FET18 is turned on again. If the abnormal condition still exists when the discharge FET18 is turned back on, a large current will flow through the discharge FET18 and trigger the battery pack protection again. Accordingly, the discharge FET18 is turned off again. Otherwise, the battery pack 22 will operate in a normal discharge mode with the discharge FET18 turned on. However, if the abnormal condition exists for a long period of time, a large current will continuously flow through the discharge FET18, which will eventually destroy the battery pack 22 and/or the MOSFET.

Accordingly, there is a need for a circuit and method for trickle precharge and/or trickle discharge, and the present invention is generally directed to such a circuit and method.

Disclosure of Invention

In one embodiment, a method is provided for protecting a battery pack from a high current overcurrent or short circuit condition. The method includes the steps of generating a control signal at the turn-on control circuit and generating a trickle discharge current under the control of the control signal if a large current over-current or short circuit condition occurs. The trickle discharge current can prevent a large current from flowing from the battery pack.

In another embodiment, another method of protecting a battery pack from a current over-current or short circuit condition is provided. The method includes the steps of a) closing the discharge switch when a high current over-current or short circuit condition occurs, b) generating a control signal at the switch control circuit, the control signal having a predetermined maximum level, c) generating a trickle discharge current under the control of the control signal, the trickle discharge current having a threshold current level and being capable of preventing the high current of the battery pack from flowing, d) detecting whether the high current over-current or short circuit condition still exists based on the trickle discharge current, the threshold current level and the predetermined maximum control level, e) repeating steps a) through d) if the high current over-current or short circuit condition still exists, and f) fully opening the discharge switch if the high current over-current or short circuit condition is removed.

Drawings

Although those skilled in the art will recognize that the following detailed description uses preferred embodiments and methods, the present invention is not limited to these preferred embodiments and methods. The scope of the claims of the present invention is defined by the appended claims.

Other features and advantages of the present invention will become more apparent as the following detailed description proceeds, and upon reference to the drawings, in which like numerals depict like parts, and in which:

FIG. 1A is a schematic diagram of typical charge process current, voltage for a lithium ion battery;

FIG. 1B is a conventional battery pre-charge circuit;

FIG. 2A is an exemplary trickle precharge circuit according to the present invention;

FIG. 2B is an exemplary trickle discharge circuit according to the present invention;

FIG. 3A is another exemplary trickle precharge circuit according to the present invention;

FIG. 3B is another exemplary trickle discharge circuit according to the present invention;

FIG. 4 is another exemplary trickle precharge circuit according to the present invention;

FIG. 5 is a typical programmable current source;

FIG. 6 is a typical trickle precharge and trickle discharge circuit;

fig. 7 is a control flow diagram of battery pack short circuit/overcurrent protection according to an embodiment of the present invention.

Detailed Description

Fig. 2A illustrates an exemplary trickle precharge circuit 100 according to the present invention. In this embodiment, two MOSFETs 104 and 102 (a charge FET CHG _ FET and a discharge FET DSG _ FET) are used. In this embodiment, the charge FET 104 and the discharge FET102 are placed in series back-to-back in the manner described. In the trickle precharge mode, the discharge FET102 is off (non-conductive), but if the charge FET (CHG _ FET)104 is on (conductive), current still flows through its body diode to the battery cell. If CHG _ FET 104 is turned off, no current flows into or out of the battery cell.

In addition to two MOSFETs, the circuit 100 may also include a reference diode D1110, a discharge driver 106, a charge driver 108, and a reference current source Iref 112. The charge driver 108 and the discharge driver 106 each include a respective comparator. In the normal charging mode, the switches K1 and K2(114 and 116) are set to position 2. In this position, the charge driving voltage CHG is driven to the reference voltage CHG _ REF, which may fully turn on the charge FET 104. Therefore, the reference voltage CHG _ REF should be selected according to the turn-on voltage of the charge FET 104.

In the trickle precharge mode, switches K1114 and K2116 may be set to position 1. When the AC adapter is connected, the VPACK + voltage will rise. The charge FET 104 may be driven into the saturation region of operation by the charge driver 108, which also means that the charge FET 104 may act as a variable resistor and a trickle charge current may flow through the charge FET 104. Charge driver 108 dynamically adjusts charge FET (CHG _ FET)104 to have voltage Vc equal to Vd set by diode D1110 and reference current source Iref 112.

Vc is the voltage at the junction of MOSFETs 102 and 104. Vc may be set as the input to the (-) negative terminal of the comparator in the charge driver 108, while Vd (set by Iref and D1) may be set as the input to the (+) positive terminal. The output signal CHG is Vd-Vc. When Vc is nearly equal to Vd, the gain of the comparator of the charge driver 108 may drive the charge FET 104 to operate in the saturation region. Thus, the charge driver 108 dynamically adjusts Vc to be equal to the fixed signal Vd during the trickle precharge period.

Under the aforementioned bias conditions, the DC current flowing through diode D1110 is given by:

Iref＝A1*IS1*(exp(Vd1/Vt)-1)

where a1 IS the junction area of diode D1, IS1 IS the diode cell reverse saturation current, Vd 1-Vcell IS the voltage drop across diode D1110, and Vt IS the diode threshold voltage. The DC current of the body diode in the discharge FET102 is given by:

Ipch＝A2*IS2*(exp(Vd2/Vt)-1)

where a2 IS the body diode junction area, IS2 IS the body diode cell reverse saturation current, and Vd2 — Vc-Vcell IS the voltage drop across the discharge FET body diode. IS1 and IS2 are determined by the type of semiconductor selected. If Vd and Vc are forced to be substantially equal, the trickle precharge current is proportional to the reference current Iref, given by:

Ipch＝A2/A1*(IS2/IS1)*Iref

preferably, although not necessary to the present invention, the junction area a2 of the body diodes of the charge and discharge FETs 102 and 104 is typically large to achieve low on-resistance and high current capability, while the junction area a1 of the diode D1 is small to save chip area. Thus, since A2 > A1, a small current Iref (tens of microamps) can be used to control a larger current Ipch (tens to hundreds of milliamps).

FIG. 2B shows a trickle discharge circuit 200 according to the present invention. This embodiment is similar to the circuit 100 depicted in fig. 2A, except that a reference current source 112 and a diode 110 are connected to the discharge FET102 terminal. During the trickle discharge period, the charge FET 104 is turned off and a trickle discharge current flows through its body diode. The operating principle of the circuit 200 is described in detail above with reference to fig. 2A.

Fig. 3A illustrates another exemplary trickle precharge circuit 300 according to the present invention. In this embodiment, the charge FET 302 and the discharge FET304 are placed in series face-to-face rather than back-to-back (as in fig. 2A). The embodiment of fig. 3A also includes a reference diode D1310, in which the charge driver 306 may be controlled by switches K1 and K2(314 and 316).

In the normal charge mode, switches K1 and K2 may be set to position 2, so that the gate voltage of the charge FET 302 is driven to CHG _ REF, fully turning on the charge FET 302. In the trickle precharge mode, the discharge FET304 is off and K1 and K2 are set to position 1. Thus, charge driver 306 may dynamically adjust charge FET 302 to force voltage Vc to be substantially equal to Vd. Under the aforementioned bias conditions, the DC current of diode D1310 is given by:

Iref＝A1*IS1*(exp(Vd1/Vt)-1)

where a1 IS the diode D1 junction area, IS1 IS the diode D1 cell reverse saturation current, Vd 1-VPAK + -Vd IS the voltage drop across diode D1, and Vt IS the diode threshold voltage. The DC current of the body diode of the discharge FET304 is:

Ipch＝A2*IS2(exp(Vd2/Vt)-1)

where a2 IS the body diode junction area, IS2 IS the body diode cell reverse saturation current, and Vd2 ═ VPACK + -Vc IS the voltage drop across the discharge FET body diode. IS1 and IS2 are determined by the type of semiconductor selected. If Vd and Vc are forced to be the same, then the trickle precharge current is given by:

Ipch＝A2/A1*(IS2/IS1)*Iref

fig. 3B illustrates an exemplary trickle discharge circuit 400 in accordance with the present invention. This embodiment is similar to the circuit 300 shown in fig. 3A, except that a reference current source 312 and a diode 310 are connected to the charge FET 302 terminal. During the trickle discharge, the charge FET 302 is off and a discharge current may flow through the body diode of the charge FET 302. The operating principle of the circuit 400 is described in detail above with reference to fig. 3A.

To accelerate the trickle precharge process, the trickle precharge current Ipch may be rapidly adjusted based on the battery voltage. The higher the battery voltage, the larger the trickle precharge current will be set by the programming reference current Iref. The circuit of fig. 5 may be used for a programmable reference current source based on the battery voltage.

Another exemplary trickle precharge circuit 500 is also depicted in fig. 4. In this embodiment, the charge FET 504 and the discharge FET 502 may be placed in series back-to-back in the manner described. In the trickle precharge mode, the discharge FET 502 is off (non-conducting), but if the charge FET (CHG _ FET)504 is on (conducting), current still flows through its body diode to the battery cell. If CHG _ FET 504 is turned off, no current flows into or out of the battery cell.

The embodiment further includes a reference resistor R1, a discharging driver 506, a charging driver 508 and a reference current source Iref 1512. The charge driver 508 and the discharge driver 506 may include respective comparators. In the normal charging mode, the switches K1 and K2(520 and 518) are set to position 1. In this position, the gate drive voltage CHG is driven to an operating point equal to the reference voltage CHG _ REF to fully turn on the charge FET 504. Therefore, the reference voltage CHG _ REF should be selected according to the turn-on characteristics of the charge FET 504.

When trickle charge (i.e., trickle precharge) is required, switches K1 and K2 are connected to node 2. The inputs to the comparator in charge driver 508 are thus the voltage across Rsens (+) and the voltage drop across R1 (produced by Iref 1512) (-). The gain of the comparator in the charge driver 508 should be designed to be large (e.g., 80dB) so that the voltage drop of Iref1 across resistor R1 is approximately equal to the voltage drop of the trickle charge current Ipch across sense resistor Rsens.

The trickle precharge current is given by:

Ipch＝Iref1*R1/Rsens

where Iref1 is a programmable current reference source. Typically Rsens is very small (e.g., like 10 to 20 milliohms), while R1 may be selected to be in the range of 10 ohms. Thus, the ratio of R1 to Rsens can be very large, so that a small reference current Iref1 can be applied to produce a relatively large trickle precharge current.

In the embodiment of fig. 4, during the trickle precharge mode, the discharge FET 502 may be fully turned on, thereby eliminating the diode forward biased voltage drop between VPACK + and the battery pack voltage. In this mode, switches K4514 and K3516 may be set to position 1 to drive the gate voltage of the discharge FET to the discharge reference voltage DSG _ REF to fully turn on discharge FET 502.

Still referring to FIG. 4, in the normal discharge mode, switches K3 and K4 may be connected to node 1, respectively. Thus, the discharge driver 506 drives the discharge FET 502 to be fully turned on. When in the trickle discharge mode, switches K3 and K4 may be connected to node 2. Due to the high gain loop of discharge driver 506, the voltage drop across resistor R2 by Iref2 is approximately equal to the voltage drop across sense resistor Rsens. Thus, the trickle discharge current is given by:

Idsg＝Iref2*R2/Rsens

where Iref2 is a programmable current reference source. In general Rsens can be very small, so the ratio of R2 to Rsens can be very large, so a small reference current Iref2 can produce a relatively large trickle discharge current. Since the current direction is reversed during discharge, the voltage drop across the sense resistor Rsens and the voltage drop across R2 have opposite polarities. Thus, the polarity reversing circuit 522 is used to reverse the polarity of the voltage across Rsens.

In this embodiment, the discharge FET 502 may be fully turned on during trickle charge. Thus the forward bias voltage of the diode between VPACK + and the battery pack voltage is eliminated. Likewise, during trickle discharge, the charge FET 504 may be fully turned on to eliminate the diode forward-biased voltage drop between the battery pack voltage and VPACK +.

In the present invention, once the MOSFETs and diodes are fixed, Ipch can still be adjusted by the programmable current sources (Iref)112, 312, 510 and/or 512. A typical circuit topology for a programmable current source is depicted in fig. 5. The circuit of fig. 5 is adapted to generate a current Iref with a ratiometric current mirror. Of course, programmable reference current sources other than the circuit of fig. 5 are well known in the art and may be implemented in a variety of ways.

An exemplary trickle precharge and trickle discharge circuit 600 is depicted in fig. 6. In this embodiment, the charge FET 604 and the discharge FET602 are placed in back-to-back series in the manner described, or alternatively in face-to-face series as previously described. In this embodiment, a digital-to-analog converter circuit (DAC)616 may be used to generate a FET drive voltage, as described more fully below.

This embodiment includes a control loop formed by an analog-to-digital converter circuit (ADC)614, a controller 612, and a digital-to-analog converter circuit (DAC) 616. The current across sense resistor Rsens 618 may be detected by ADC 614. The ADC 614, in turn, may generate digital signals representative of the current and send these signals to the controller 612. In operation, if the current through sense resistor 618 is less than a predetermined threshold, the controller may send data to DAC616 to increase the corresponding FET drive voltage. Instead, it will send data to the DAC616 to reduce the FET drive voltage until the sense current and the predetermined current are approximately equal.

In the normal charge or discharge mode, the DAC616 is disabled (controlled by the DAC _ EN signal received by the DAC 616), and the charge FET 604 and the discharge FET602 are fully turned on. The charge driver 608 drives the gate voltage of the charge FET 604 to the CHG _ REF value and fully turns on the charge FET 604. Discharge driver 606 drives the gate voltage of discharge FET602 to the DSG _ REF value and fully turns on discharge FET 602.

In the trickle discharge mode, switch K1620 is connected to node 1. The discharge driver 606 is disabled (DSG _ EN low) and the output is high impedance, at which time the conduction state of the discharge FET602 can be controlled by the DAC 616. Thus, the discharge FET602, sense resistor Rsens 618, ADC 614 and DAC616 may form a control loop. By controlling the turn-on resistance of the discharge FET602, the present invention can adjust the trickle discharge current to a preset value (which may be preprogrammed into the controller 612). The on-resistance of the MOSFET can be adjusted by adjusting the gate drive voltage.

In one embodiment, if the required trickle discharge current is set to Itd, then the corresponding control code for controlling DAC616 may be obtained using SAR (successive approximation register) methods. The MSB (most significant bit) of the DAC is first set high and if the current Isen through sense resistor Rsens 618 is greater than Itd, then the MSB bit is set low, otherwise it will remain high. The second MSB bit is then set to high, if Isen > Itd, the second MSB bit is set to low, otherwise it will remain high. This successive approximation will continue until the LSB (least significant bit) of the DAC is set. The corresponding control code may be stored in a register (not shown) and thus may be accessed by the controller 612. If Itd is set for a given battery pack, the control code may also be set. Whenever a trickle discharge is required, the controller 612 may send a programmed control code to the DAC616, so the battery pack will be able to pass Itd to an external load. If the trickle discharge current needs to be adjusted, the control loop described above can be used to increase or decrease the control code accordingly. In the trickle discharge mode, the charge driver 608 may be enabled or disabled. The difference is that a trickle discharge current will flow through the charge FET 604 or its body diode, respectively.

In trickle charge mode, switch K1620 is connected to node 2. The charge driver 608 is disabled (CHG _ EN is low). The conduction state of the charge FET 604 may be controlled by the DAC 616. In this mode, the charge FET 604, sense resistor Rsens 618, ADC 614 and DAC616 form a control loop. By controlling the turn-on resistance of the charge FET 604, the present embodiment is able to adjust the trickle charge current to a set value. The precharge current is typically a fixed value. In this mode, the present embodiment may generate a control code (using the SAR method described above) and save the control code in memory. For trickle precharge currents, the value may vary between some upper limit to a lower limit, and therefore the code is controlled at C accordingly_TCHAnd C_TCLThereby allowing the trickle charge current to be adjusted accordingly. The discharge driver 606 may also be enabled or disabled in the trickle charge mode. The difference is that the trickle charge current flows through the discharge FET602 or its body diode, respectively.

The trickle discharge mode described above may be further applied to achieve battery pack short circuit/overcurrent protection. The first embodiment described below is effective for battery pack protection when the battery pack is removed from the electronic system (i.e., when the battery pack is in an idle state). Unlike conventional methods of keeping the discharge FET602 off, this embodiment sets the discharge FET602 to a controllable conduction state. When the discharge FET602 is in a controllably conductive state, a large current surge is prevented by the discharge FET602 turn-on resistance even if a short circuit condition occurs, i.e., the VPACK + terminal is shorted to the VPACK-terminal. Similarly, high current surges are prevented when overcurrent conditions occur. In practice, when a short circuit/overcurrent condition occurs, a trickle discharge current will flow through the discharge FET602, which can be set to a set value to ensure safety of the battery pack and MOSFETs. For example, setting the trickle discharge current to 100mA enables driving an external controller (which is different from the controller 612 shown in fig. 6) embedded in the electronic system. When the battery pack is inserted into the electronic system, the embedded controller can detect the insertion of the battery pack and notify the battery pack to enter a normal discharge mode. Thus, no additional mechanical means or electronic circuitry is required to detect insertion of the battery pack. However, this embodiment does not further provide battery short/overcurrent protection when the battery pack is inserted into an electronic system. This embodiment is thus advantageous only when the battery pack is removed from the electronic system.

A second embodiment of battery pack protection is depicted by a flow chart 700 shown in fig. 7. It is effective both when the battery pack is removed from the electronic system and when the battery pack is inserted into the electronic system. Initially, as shown in step 702, the battery pack is either in an idle state (e.g., it is removed from the electronic system) or in a normal discharge mode (e.g., it is inserted into the electronic system). Regardless of which mode the battery pack is in, step 704 determines the short circuit/overcurrent occurrence behavior. If no short circuit/overcurrent condition occurs, the battery pack will stay in an idle or discharge mode. If a short circuit/overcurrent condition exists, step 706 immediately turns off the discharging FET 602. Typically, the discharge FET602 may be turned off within a few microseconds. Then, in step 708, if the discharge FET602 has been turned off for a predetermined time, e.g., 25 seconds, the discharge FET602 will be driven to a controlled conduction state, unlike conventional methods that immediately turn the discharge FET602 fully on. When the discharging FET602 is in a controllably conductive state, the battery pack will operate in a trickle discharge mode as a trickle discharge current flows through the discharging FET602 in step 710. If the predetermined time has not expired, the discharge FET602 remains in the OFF state.

Those skilled in the art will recognize that to implement step 708, the embodiment shown in FIG. 6 may include a battery management firmware and a timer. The battery management firmware is able to monitor hardware actions. The timer has a preset time (e.g., 25 seconds). If a short circuit/overcurrent condition occurs, the battery management firmware will be informed that the discharge FET602 has been turned off and then start a timer. If the preset time of the timer expires, the management firmware is informed that the discharging FET602 has been turned off for a predetermined length of time.

In the trickle discharge mode, the DAC616 in FIG. 6 provides a gate drive voltage to the discharge FET 602. Thereby causing the discharge FET602 to operate in a controllably conductive state. By adjusting the gate drive voltage, the on-resistance of the discharge FET602 is adjusted, and thus the trickle discharge current flowing through the discharge FET602 is adjusted accordingly.

In the trickle discharge mode, the following steps may be included. Initially, under the control of the controller 612, the gate drive voltage control code from the DAC616 is set to 0 in step 712. Then, the gate drive voltage control code is gradually increased in step 714. From the characteristics of the MOSFET, those skilled in the art will readily appreciate that the on-resistance of the discharge FET602 will gradually decrease as the gate drive voltage control code increases, and in turn the trickle discharge current flowing through the discharge FET602 will gradually increase. Each time the gate drive voltage control code is incremented, the voltage of the corresponding trickle current across resistor Rsens 618 is detected and then used to determine if a short circuit/over current condition exists.

In particular, in step 716, the trickle discharge current is compared to a predetermined current, e.g., 40 milliamps, for determining whether a short circuit/overcurrent condition exists. If the trickle discharge current is greater than the predetermined current, it can be concluded that a short circuit/over current condition still exists. The system shown in fig. 6 then restarts the battery pack protection through the operation of step 706. If the trickle discharge current is less than the predetermined current, the gate drive voltage control code will be compared to the predetermined maximum control code in step 718. In fact, the gate driving voltage control code will not be increased without limit, but will be limited to a predetermined maximum control code. In step 718, if the gate drive voltage control code reaches a predetermined maximum control code, it can be concluded that the short circuit/overcurrent condition no longer exists in step 702 and the battery pack will return to the idle mode or normal discharge mode. Otherwise, the battery pack will repeat steps 714, 716, and 718 until the trickle discharge mode is exited due to either a determination that a short circuit/overcurrent condition exists in step 716 or a determination that a short circuit/overcurrent condition does not exist in step 718.

The predetermined current here is set by taking into account the power dissipation performance of the MOSFET. For the four cell battery shown in fig. 6, the predetermined current may be set to 40 milliamps, so that the maximum power dissipation of the discharge FET602 is approximately 680 milliwatts, which is a safe value for the power MOSFET.

In addition, the voltage at the VPACK + terminal may also be applied to determine whether a short circuit/overcurrent condition exists. In step 716, the voltage at the VPACK + terminal is detected and compared to a predetermined voltage, e.g., 100 millivolts. If the voltage at the VPACK + terminal is less than the predetermined voltage, it can be concluded that a short circuit/over current condition still exists. Otherwise, the gate drive voltage is compared to a predetermined maximum control code in step 718. The predetermined voltage at the VPACK + terminal is set in consideration of noise and internal battery resistance. For the embodiment of fig. 6, the predetermined voltage is set to 100 millivolts, which is a good compromise between the short circuit/over current condition and the amount of noise and battery internal resistance.

From fig. 1A, it is known that the charging current needs to be controlled during pre-charging and during Constant Voltage (CV) charging. In conventional circuits, an additional precharge FET is required to control the precharge current. In such conventional circuits, CV charging must rely entirely on the charger to precisely regulate the charging voltage to V_OVThe charging current will then be decremented.

In this embodiment, no additional precharge FET precharge function is implemented. In addition, to accelerate the precharge process, the precharge current Ipch may be easily adjusted based on the battery voltage. The higher the battery voltage, the larger the pre-charge current is set by programming the reference current Iref, such as the control code method described herein with reference to fig. 2A, 3A and 4, or 6.

Further, as described in numerous embodiments herein, the trickle charge current control may also be utilized during a CV period during which the trickle charge circuit is capable of generating the trickle charge current based on the battery voltage. As such, the CV charging current ramp down does not require the charger to be relied upon to accurately regulate the voltage V_OV. Thus, several embodiments of the present invention may eliminate the need for expensive, accurate voltage regulation chargers. Indeed, a simple AC adapter may be applied to charge a lithium ion battery. Since even the charger cannot fix the constant voltage at V during CV charging_OVBut the charging current is limited to a pre-programmed trickle current value determined based on the battery voltage. Therefore, overcharging does not occur. This charge current limit can be used as a second tier overvoltage protection (by setting the current limit to be higher than at voltage V_OVSlightly larger than the actual observed current value) or as first layer overvoltage protection (by adjusting the charging current until the exact desired V is obtained)_OV)。

With the trickle discharge performance of the present invention, better short circuit/overcurrent protection for the battery pack is possible. In the prior art, the discharge FET is either fully on to allow discharge or fully off to inhibit discharge. When the battery pack is removed from the electronic system, for example, on a stand, the discharge FET is either left on ready to power the electronic system whenever the battery pack is inserted into the electronic system. In this case, if an abnormal condition occurs, such as the VPACK + terminal being shorted to the VPACK-terminal, a large current is discharged from the battery, and thus, the battery is damaged; or the discharge FET remains off to protect the battery from short circuit/overcurrent conditions. But this will prevent the battery from powering the system when the battery pack is inserted into the system. Some technical approach is needed to inform the battery to return to the on discharge FET state. This causes inconvenience to the customer and increases costs.

Using the present invention we can place the battery pack into a trickle discharge mode when the battery is removed from the electronic system. The trickle discharge current value may be chosen to be large enough to power the system embedded controller when the battery pack is plugged into the electronic system, assuming 100 milliamps. The embedded controller system will then detect the presence of the battery and notify the battery to transition to the normal discharge mode. With the discharge FET limiting the current to a predetermined trickle discharge current, a large current surge is prevented even if the VPACK + terminal is shorted to the VPACK-terminal, assuming 100 milliamps.

Also, the battery pack of the present invention can prevent the battery pack from suffering from abnormal situations, such as short circuit/overcurrent situations, regardless of whether the battery pack is taken out of or in an electronic system. Initially, the discharge FET is turned off when an abnormal condition occurs. Then, after a predetermined period of off time, the discharge FET is driven to a controlled conduction state, rather than being fully on as in the conventional approach. Thus, the battery pack will operate in the trickle discharge mode. The gate driving voltage gradually increases and the corresponding trickle discharge current increases accordingly. In this process, if the corresponding trickle discharge current becomes greater than the predetermined current, assuming 40 milliamps, it can be concluded that the abnormal condition continues, and therefore the discharge FET will turn off again and the battery pack will repeat the above operation. If the gate driving voltage is increased to a predetermined maximum control voltage and the corresponding trickle discharge current has not reached the predetermined current, it may be determined that the abnormal condition has been eliminated and the battery pack may be operated in the normal discharge mode.

The trickle discharge and trickle charge capabilities are very useful for systems supporting multiple batteries. As electronic systems require more power and more features, multi-battery packs will become more popular. When multiple battery packs are discharged simultaneously, they can provide more power to the system, and since multiple battery packs are in parallel it will also reduce the internal cell resistance to improve efficiency. However, the simultaneous discharge of a plurality of battery packs has a strict precondition that these battery packs must have exactly the same voltage. Otherwise, even if two battery packs have only a small voltage difference, say 10 millivolts, since the resistance of the power bus is small, say 2 milliohms, it will have a large current, 5 amps, which will flow from the battery pack having the higher voltage into the battery pack having the lower voltage. In practice, it is difficult for multiple battery packs to have the same voltage, and even if two battery packs have a very accurate ADC to monitor the battery voltages, it is difficult to assume that they have the same voltage because the battery pack voltages vary with the discharge current. With the application of the trickle discharge function, we can solve the following problem (we take two battery packs as an example).

The system has two battery packs, battery pack a and battery pack B. Initially, pack a voltage is higher than pack B voltage; the battery pack A supplies power to the system firstly, and the voltage of the battery pack A is gradually reduced. The discharge FET of battery B is turned off to inhibit discharging; when the battery pack A voltage drops to the same voltage as the battery pack B voltage, we set the battery pack B to either a trickle charge mode or a trickle discharge mode. If we set battery B to trickle charge mode, we can turn on the discharge FET completely, driving the charge FET to its saturation region of operation and using the charge FET as a current limiting resistor; if we set battery pack B to the trickle discharge mode, we turn on the charge FET completely and drive the discharge FET to its saturated operating region and have the discharge FET as a current limiting resistor. For many safety reasons, we can use the trickle charge control code C_TCOr trickle discharge control code C_TDSet to a small current value. So that the equivalent resistance of the charge FET or the discharge FET becomes larger. Since battery a is discharging but battery B is in idle mode, even though their measured voltages are the same, the actual battery a voltage will be higher than the battery B voltage. Therefore, battery pack a will charge battery pack B. However, the charging current is limited by the resistance of the charging FET (if the battery pack B is set to the trickle charge mode) or the discharging FET (if the battery pack B is set to the trickle discharge mode). The limited current value being controlled by a control code C_TCOr C_TDAnd (4) determining. We also monitor this charging current through the ADC in battery B; as the voltage difference between the battery packs a and B becomes smaller and smaller, the charging current from the battery pack a to the battery pack B becomes smaller and smaller. When the charging current is less than a predetermined value, we can assume 10 milliampsTo transition the battery pack B from the trickle charge mode or the trickle discharge mode to the normal discharge mode.

Thus, the disclosed programmable trickle precharge and/or trickle discharge circuits and methods may provide more flexibility, fewer components, and greater efficiency to accomplish precharging than conventional circuit configurations. Based on the amount of charge of the battery cell (deeply discharged batteries require a trickle charge mode), in fig. 2A and 2B, the switches (K1, K2 and/or K3 and K4) may be controlled by the battery monitor IC to set the programmable trickle charge circuit to either a trickle precharge mode or a normal charge mode. It is further understood that the circuit structures described herein may be implemented using discrete devices and/or integrated circuits. The invention is applicable to any portable electronic device (portable computer, cell phone, PDA, etc.) that uses a rechargeable battery.

The specific circuit topology mentioned here is only a typical example, and other trickle charge/discharge circuit topologies may be applied. Likewise, many variations and modifications of the circuit are possible based on the exemplary trickle charge/discharge circuit described herein without departing from the spirit of the invention. All such modifications are intended to be included within the scope of this invention, which is defined in the following claims.

Claims (10)

1. A method for protecting a battery pack from a high-current overcurrent or short-circuit condition is characterized by comprising the following steps:

a) closing the discharge switch when a large current overcurrent or short circuit occurs;

b) generating a control signal at the switch control circuit, wherein the control signal has a preset highest level;

c) generating a trickle discharge current under the control of the control signal, wherein the trickle discharge current has a threshold current level and can prevent the large current from flowing in the battery pack;

d) detecting whether a large current overcurrent or short circuit condition exists according to the trickle discharge current, the threshold current level and the preset highest level;

e) repeating the steps a) to d) if the large-current overcurrent or short-circuit condition still exists;

f) and if the large current overcurrent or short circuit condition is eliminated, the discharge switch is turned on.

2. The method of claim 1, further comprising the steps of:

setting a timer; and

a trickle discharge current is generated when the timer expires.

3. The method of claim 1, wherein the step of generating the trickle discharge current further comprises setting a discharge switch to a controllably conductive state under control of a control signal.

4. The method of claim 1, further comprising adjusting the trickle discharge current according to the control signal.

5. The method of claim 4, wherein the step of adjusting the trickle discharge current further comprises:

adjusting the resistance of a discharge switch according to the control signal; and

the trickle discharge current is adjusted according to the resistance of the discharge switch.

6. The method of claim 1, wherein a large current over-current or short circuit condition exists if the trickle discharge current is at least equal to a threshold current level.

7. A method according to claim 1, characterized in that a high current over-current or short-circuit condition is eliminated if the control signal is at least equal to a predetermined maximum level.

8. The method of claim 1, wherein step (d) further comprises the steps of:

1) detecting a trickle discharge current;

2) comparing the trickle discharge current to a threshold current level;

3) comparing the control signal to a predetermined maximum level if the trickle discharge current is less than the threshold current level;

4) increasing the control signal if the control signal is less than a predetermined maximum level;

5) repeating steps 1) through 4) if the trickle discharge current is less than the threshold current level and the control signal is less than a predetermined maximum level.

9. The method of claim 1, wherein step (d) further comprises the steps of:

i, detecting voltage at the positive terminal of the battery pack;

II comparing the voltage with a threshold voltage level;

III comparing the control signal with a predetermined maximum level if the voltage is above the threshold voltage level;

IV increasing the control signal if the control signal is less than a predetermined maximum level;

v if the voltage is greater than the threshold voltage level and the control signal is less than the predetermined maximum level then steps I to IV are repeated.

10. The method of claim 9, wherein a high current over-current or short circuit condition exists if the voltage is at most equal to the threshold voltage level.