A charge-discharge implementation method suitable for series battery combination

Abstract

The application belongs to the technical field of battery management charging, and particularly relates to a charging and discharging implementation method suitable for a series battery combination. The application proposes a charging scheme combining a linear charging mode and a charge pump mode, and adopts the linear charging mode to trickle charge the battery in a low-voltage state of the battery, and meanwhile, adds a pull-down current source at an output end of a BATFET to achieve the purpose of VBATL voltage clamping. When the battery voltage is charged to reach the level of activating a lithium battery protection switch, the system judges to exit the linear charging mechanism and enters a switched capacitor charging mode. The application can better solve the problem of large current that may occur in a dead battery state, so as to improve charging safety and reliability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery management charging, and particularly relates to a charging and discharging implementation method suitable for a series battery combination. BACKGROUND

[0002] The charging and discharging topology architecture of the 2S battery combination is shown in Figure 1 (a), the adapter output power VAC is supplied to the system power VSYS through a step-down inductive DC-DC BUCK, and the battery pack is charged through the BATFET switch and the 1:2 charge pump CP. The BATFET switch can adjust the charging current, and the CP connects the battery after the BUCK output VBATL is stepped up by 1:2. When the adapter VAC is not in place, the battery pack enters the discharging mode, the BATFET is configured in the bypass mode, and the battery voltage is supplied to the system power VSYS after being stepped down by 2:1.

[0003] The charge pump circuit topology is shown in Figure 1 (b), which mainly consists of four power switches and a FLY capacitor. In the charging mode, PHASE1 QC2 and QC4 are turned on, VBATL charges the FLY capacitor, PHASE2 QC1 and QC3 are turned on, and the FLY capacitor discharges the battery VBATH; in the discharging mode, PHASE1 QC1 and QC3 are turned on, the battery VBATH charges the FLY capacitor, PHASE2 QC2 and QC4 are turned on, and the FLY capacitor discharges the output VBATL.

[0004] The 2S battery combination charging and discharging circuit topology is shown in Figure 2 (a), QB0, QB1 and inductor Lb form a BUCK structure. When the double battery is in an ultra-low power or dead battery state, the VBATH node usually exhibits a very low voltage (e.g. VBATH < 2V), at which time the system is powered off, and the VBATL and VSYS voltages are in a powered-off state. When the adapter VAC is inserted, the VBATL voltage is charged by the charging loop of the buck charger until the VBAT CV state (the CV voltage is usually designed at about 4.4V), and during the VBATL voltage boosting process, the BATFET charging current (the BATFET charging current usually reaches the order of 4A during the fast charging process) enters the battery pack through the body diodes of QC1 and QC2, and when the VBATL voltage reaches the CV point, the charging current finally decreases to a low current state.

[0005] In the dead battery state, trickle charging (the trickle current is usually less than 100 mA) is usually needed to activate the battery, so as to improve the safety and prolong the life of the battery. The charging solution has the disadvantage that the fast charging mode large current may appear in the dead battery state. In the process of activating the dead battery by inserting the adapter, the fast charging current enters the battery pack through the body diode of the two power tubes, thereby affecting the safety and life of the battery. SUMMARY

[0006] The application provides a charging solution combining linear charging and charge pump mode. In the low-voltage state of the battery, the linear charging mode is used to trickle charge the battery, and at the same time, a pull-down current source is added at the output end of the BATFET to achieve the purpose of VBATL voltage clamping. When the battery voltage reaches the level of activating the lithium battery protection switch, the system judges to exit the linear charging mechanism and enters the switched capacitor charging mode.

[0007] In view of the above problems, the technical scheme of the application is:

[0008] A charging and discharging implementation method suitable for a series battery combination, which adopts a linear charging and charge pump charging and discharging combined mode to charge and discharge the series battery combination when the adapter is inserted.

[0009] The condition for adopting the linear charging is that after the adapter is inserted, whether the battery pack voltage is lower than a preset first threshold voltage VTH1 is detected. If yes, the linear charging stage is entered, otherwise whether the battery voltage is higher than a preset second threshold voltage VTH2 is judged. If yes, the charge pump discharging mode is entered, otherwise the charge pump charging mode is entered.

[0010] The implementation method of the linear charging is that a first current source is connected to the low-voltage output side of the charge pump, the first current source is controlled by a first switch tube, the output end of the first current source is grounded, and the input end is connected to the low-voltage output side of the charge pump through the first switch tube. The first current source is used for clamping and is a pull-down current source. A second current source is connected to the high-voltage output side of the charge pump, the second current source is controlled by a second switch tube, the input end of the second current source is connected to the adapter voltage through the second switch tube, and the output end of the second current source is connected to the high-voltage output side of the charge pump and the positive electrode of the series battery combination. The second current source is a current limiting loop. When it is detected that the battery pack voltage is lower than the first threshold voltage VTH1, the first switch tube and the second switch tube are turned on, the low-voltage output side of the charge pump remains in the state clamped by the pull-down current source, and the battery voltage linearly rises.

[0011] The charge pump charging mode is that when the battery pack voltage is greater than the first threshold voltage VTH1 and less than the second threshold voltage VTH2, the linear charging mode is exited and the charge pump charging mode is entered, at this time, the first switch tube is kept on, the second switch tube is turned off, and the charge pump enters the soft start mode; when the charge pump soft start ends, the first switch tube and the second switch tube are both turned off, and the charge pump charging mode is entered;

[0012] The charge pump discharging mode is that when the battery pack voltage is greater than the second threshold voltage VTH2 or the adapter is pulled out, the charge pump discharging mode is entered.

[0013] The present application has the beneficial effect that the present application proposes a charging scheme combining the linear charging and the charge pump mode, the linear charging mode is used to trickle charge the battery in the low voltage state of the battery, when the battery voltage is charged to the level of activating the lithium battery protection switch, the system judges to exit the linear charging mechanism and enters the switched capacitor charging mode, the charging scheme can better solve the large current problem that may occur in the dead battery state, so as to improve the charging safety and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a traditional charging and discharging topology architecture, wherein (a) is a charging and discharging topology architecture of a 2S battery combination, and (b) is a charge pump circuit topology;

[0015] Figure 2 It is a 2S battery combination charging and discharging circuit, wherein (a) is a circuit topology structure, and (b) is a battery power consumption state charging I-V curve;

[0016] Figure 3 It is an adapter voltage VAC, VBATL and VBATH charging full process voltage waveform schematic diagram;

[0017] Figure 4 It is a linear charging implementation scheme of the present application;

[0018] Figure 5 It is a sink current source and a linear charging circuit, wherein (a) is a linear charging loop, and (b) is a sink current loop;

[0019] Figure 6 It is a system state machine schematic diagram. DETAILED DESCRIPTION

[0020] The present application will be described in detail below in combination with the drawings and embodiments.

[0021] Embodiment

[0022] The example is based on the charging and discharging scheme of two series battery combination, and the method comprises: adapter insertion, system judgment into charging mode, step-down inductance type dc-dc output first branch to system PMIC power supply, the second branch passes through 1:2 charge pump after boosting to charge the battery pack, the current limiting loop of BATFET can play the role of adjusting the charging current; adapter is pulled out, the battery voltage meets certain voltage detection requirement, the system judges to enter the discharging mode, the battery pack is boosted after 2:1 charge pump and is powered to the system through BATFET switch, and BATFET keeps straight-through state.

[0023] In the example, when the system detects that the adapter is inserted and the battery voltage is lower than the first threshold voltage, the state machine judges to enter the linear charging mode; when the system detects that the adapter is inserted and the battery voltage is higher than the first threshold voltage, the state machine judges to enter the charge pump charging mode; when the system detects that the battery voltage is higher than the second threshold voltage, the state machine judges to enter the charge pump charging mode when the adapter is inserted, and the state machine judges to automatically switch into the discharging mode when the adapter is pulled out.

[0024] The linear charging mode of the example is realized: a sink current source is designed on the low-voltage output side VBATL of the charge pump to play the role of clamping, the pull-down capability of the current source needs to be higher than the trickle charging capability of the previous charger, and the pull-down current source switch impedance design needs to meet the condition that the VBATL clamping voltage is not higher than 2V; a linear current limiting loop is designed on the high-voltage input side VBATH of the charge pump to charge the battery, and the current limiting loop can take power from the adapter VAC.

[0025] In the example, the input and output of the charge pump maintain a 1:2 conversion ratio relationship, and the battery charging current is equal to one-half of the BATFET limiting current value.

[0026] The voltage waveforms of the full charging process VAC, VBATL and VBATH are as shown in Figure 3 The adapter VAC is inserted, when it is detected that the battery voltage VBATH is lower than VTH1, the state machine judges to enter the linear charging phase, the VBATL voltage remains in the state of being clamped by the pull-down current source, and the battery voltage VBATH linearly rises; when the battery voltage VBATH rises to be higher than VTH1, the linear charging mode is exited, the charge pump charging mode is entered, the voltages VBATH and VBATL maintain a 2:1 conversion ratio, and when the battery voltage VBATH is charged to be higher than VTH2, the charge pump can automatically switch into the discharging mode.

[0027] The specific implementation scheme of the linear charging is as shown in Figure 4 The EN_SINK signal controls the opening or closing of the sink current, and the EN_LNCHG signal controls the opening or closing of the charging current; specifically, the sink current source and the linear charging circuit are realized as shown inFigure 5 As shown, the current source can be realized by a reference current IB and a resistive amplification ratio.

[0028] The system state machine is as shown in the figure. Figure 6 As shown, when the state machine detects that the adapter is inserted and the battery voltage VBATH is lower than the first threshold voltage VTH1, the state machine determines to enter the linear charging mode, the logic signals EN_SINK and EN_LNCHG are set high, and when the linear charging duration exceeds the timeout protection time, the system reports a Time-out state and stops charging; when the battery voltage is charged to be higher than the first threshold voltage VTH1, the system determines to exit the linear charging mode, the logic signal EN_SINK remains in the high state, EN_LNCHG is set low, and the charge pump enters the soft start mode; when the charge pump soft start ends, the logic signals EN_SINK and EN_LNCHG are both low, and the charge pump charging mode is entered; when the battery voltage VBATH is charged to be higher than the second threshold voltage VTH2, the adapter VAC is pulled out, and the system automatically determines to enter the discharging mode; when abnormal conditions such as overload or output short circuit occur in the charge pump discharging mode, the system protection is triggered, the charge pump power stage is turned off, the system enters the waiting state, and after the timer is full, the state machine detection is restarted.

[0029] It should be noted that the scheme of the present application is not limited to two battery packs, and as long as the charge pump satisfies the N:1 conversion ratio relationship, it is also applicable to N-level battery packs.

Claims

1. A charge-discharge implementation method suitable for a series battery combination, characterized by, The linear charging and charge pump charging and discharging are combined to charge and discharge the series battery when the adapter is inserted; The linear charging is used when the adapter is inserted, and the battery voltage is detected to be lower than the preset first threshold voltage VTH1, if yes, the linear charging stage is entered, otherwise, the battery voltage is detected to be higher than the preset second threshold voltage VTH2, if yes, the charge pump discharging mode is entered, otherwise, the charge pump charging mode is entered; The linear charging is realized by connecting the first current source at the low voltage output side of the charge pump, the first current source is controlled by the first switch tube, the output end of the first current source is grounded, the input end is connected to the low voltage output side of the charge pump through the first switch tube, the first current source is used for clamping and is a pull-down current source; the second current source is connected at the high voltage output side of the charge pump, the second current source is controlled by the second switch tube, the input end of the second current source is connected to the adapter voltage through the second switch tube, the output end of the second current source is connected to the high voltage output side of the charge pump and the positive electrode of the series battery, the second current source is a current limiting loop; when the battery voltage is detected to be lower than the first threshold voltage VTH1, the first switch tube and the second switch tube are turned on, the low voltage output side of the charge pump is kept in the state of being clamped by the pull-down current source, and the battery voltage is linearly increased; The charge pump charging mode is entered when the battery voltage is greater than the first threshold voltage VTH1 and less than the second threshold voltage VTH2, the first switch tube is kept on, the second switch tube is turned off, and the charge pump enters the soft start mode; when the charge pump soft start ends, the first switch tube and the second switch tube are both turned off, and the charge pump charging mode is entered; The charge pump discharging mode is entered when the battery voltage is greater than the second threshold voltage VTH2 or the adapter is pulled out.

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