XB5353A

XB5353A

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to stop charging. This condition is called the overcharge condition. The overcharge condition is released in the following two cases:

1, When the battery voltage drops below the overcharge release voltage (VCL), the XB5353 turns the charging control FET on and returns to the normal condition. 2, When a load is connected and

discharging starts, the XB5353 turns the charging control FET on and returns to the normal condition. The release mechanism is as follows: the discharging current flows through an internal parasitic diode of the charging FET immediately after a load is connected and discharging starts, and the VM pin voltage increases about 0.7 V (forward voltage of the diode) from the

GND pin voltage momentarily. The XB5353 detects this voltage and releases the

overcharge condition. Consequently, in the case that the battery voltage is equal to or lower than the overcharge detection voltage (VCU), the XB5353returns to the normal condition immediately, but in the case the battery voltage is higher than the overcharge detection voltage (VCU),the chip does not return to the normal condition until the battery voltage drops below the overcharge detection voltage (VCU) even if the load is connected. In addition, if the VM pin voltage is equal to or lower than the overcurrent 1 detection voltage when a load is connected and discharging starts, the chip does not return to the normal condition.

Remark If the battery is charged to a voltage higher than the overcharge detection voltage (VCU) and the battery voltage does not drops below the overcharge detection voltage (VCU) even when a heavy load, which causes an overcurrent, is

connected, the overcurrent 1 and overcurrent 2 do not work until the battery voltage drops below the overcharge detection voltage (VCU). Since an actual battery has, however, an internal impedance of several dozens of mΩ, and the battery voltage drops immediately after a heavy load which causes an overcurrent is connected, the overcurrent 1 and

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overcurrent 2 work. Detection of load short-circuiting works regardless of the battery voltage.

Overdischarge Condition

When the battery voltage drops below the overdischarge detection voltage (VDL)

during discharging under normal condition and it continues for the overdischarge detection delay time (tDL) or longer, the XB5353 turns the discharging control FET off and stops discharging. This condition is called overdischarge condition. After the discharging control FET is turned off, the VM pin is pulled up by the RVMD resistor between VM and VDD in XB5353.

Meanwhile when VM is bigger than 1.5 V (typ.) (the load short-circuiting detection voltage), the current of the chip is reduced to the power-down current (IPDN). This condition is called power-down condition. The VM and VDD pins are shorted by the RVMD resistor in the IC under the

overdischarge and power-down conditions. The power-down condition is released when a charger is connected and the

potential difference between VM and VDD becomes 1.3 V (typ.) or higher (load short-circuiting detection voltage). At this time, the FET is still off. When the battery voltage becomes the overdischarge

detection voltage (VDL) or higher (see note), the XB5353 turns the FET on and changes to the normal condition from the overdischarge condition.

Remark If the VM pin voltage is no less than the charger detection voltage (VCHA), when the battery under overdischarge condition is connected to a charger, the overdischarge condition is released (the discharging control FET is turned on) as usual, provided that the battery voltage reaches the overdischarge release voltage (VDU) or higher.

Overcurrent Condition

When the discharging current becomes equal to or higher than a specified value (the VM pin voltage is equal to or higher than the overcurrent detection voltage)

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XB5353A

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during discharging under normal condition and the state continues for the overcurrent detection delay time or longer, the XB5353 turns off the discharging control FET to stop discharging. This condition is called overcurrent condition. (The overcurrent includes overcurrent, or load short-circuiting.)

The VM and GND pins are shorted internally by the RVMS resistor under the overcurrent condition. When a load is connected, the VM pin voltage equals the VDD voltage due to the load.

The overcurrent condition returns to the normal condition when the load is released and the impedance between the B+ and B- pins becomes higher than the automatic recoverable impedance. When the load is removed, the VM pin goes back to the GND potential since the VM pin is shorted the GND pin with the RVMS resistor.

Detecting that the VM pin potential is lower than the overcurrent detection voltage (VIOV), the IC returns to the normal condition.

Abnormal Charge Current Detection If the VM pin voltage drops below the charger detection voltage (VCHA) during charging under the normal condition and it continues for the overcharge detection

delay time (tCU) or longer, the XB5353 turns the charging control FET off and stops charging. This action is called abnormal charge current detection.

Abnormal charge current detection works when the discharging control FET is on and the VM pin voltage drops below the charger detection voltage (VCHA). When an abnormal charge current flows into a

battery in the overdischarge condition, the XB5353 consequently turns the charging control FET off and stops charging after the battery voltage becomes the

overdischarge detection voltage and the overcharge detection delay time (tCU)

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Abnormal charge current detection is released when the voltage difference between VM pin and GND pin becomes lower than the charger detection voltage (VCHA) by separating the charger. Since the 0 V battery charging function has higher priority than the abnormal charge current detection function, abnormal charge

current may not be detected by the product with the 0 V battery charging function while the battery voltage is low.

Load Short-circuiting condition

If voltage of VM pin is equal or below short circuiting protection voltage (VSHORT), the XB5353 will stop discharging and battery is disconnected from load. The maximum delay time to switch current off is tSHORT. This status is released when voltage of VM pin is higher than short protection voltage (VSHORT), such as when disconnecting the load.

Delay Circuits

The detection delay time for overdischarge current 2 and load short-circuiting starts when overdischarge current 1 is detected. As soon as overdischarge current 2 or load short-circuiting is detected over detection delay time for overdischarge current 2 or load short- circuiting, the XB5353 stops discharging. When battery voltage falls below overdischarge detection voltage due to overdischarge current, the XB5353 stop discharging by overdischarge current

detection. In this case the recovery of battery voltage is so slow that if battery voltage after overdischarge voltage detection delay time is still lower than overdischarge detection voltage, the XB5353 shifts to power-down.

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XB5353A

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Figure 4. Overcurrent delay time

0V Battery Charging Function (1) (2) (3) This function enables the charging of a connected battery whose voltage is 0 V by self-discharge. When a charger having 0 V battery start charging charger voltage

(V0CHA) or higher is connected between B+ and B- pins, the charging control FET gate is fixed to VDD potential. When the voltage between the gate and the source of the charging control FET becomes equal to or higher than the turn-on voltage by the charger voltage, the charging control FET is turned on to start charging. At this time,

XySemi Inc - 7 - the discharging control FET is off and the charging current flows through the internal parasitic diode in the discharging control FET. If the battery voltage becomes equal to or higher than the overdischarge release voltage (VDU), the normal condition returns.

Note

(1) Some battery providers do not recommend

charging of completely discharged batteries. Please refer to battery providers before the selection of 0 V battery charging function.

(2) The 0V battery charging function has higher priority than the abnormal charge current detection function. Consequently, a product with the 0 V battery charging function charges a battery and abnormal charge current cannot be detected during the battery voltage is low (at most 1.8 V or lower).

(3) When a battery is connected to the IC for the first time, the IC may not enter the normal condition in which discharging is possible. In this case, set the VM pin voltage equal to the GND voltage (short the VM and GND pins or connect a charger) to enter the normal condition.

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XB5353A

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1．

Overcharge and overdischarge detection

VCUVCU-VHCBatteryvoltageVDL+VDHVDL ON

DISCHARGE

OFF ON

CHARGE

OFFVDDVMVov1

VSSVCHACharger connectionLoad connection(1)

tCU(2)(1)tCL(3)(1)

Figure5-1 Overcharge and Overdischarge Voltage Detection

2． Overdischarge current detection

VCU

VCU-VHCVDL+VDHVDL

Battery voltage ON

DISCHARGE

OFFVDD

VSHORTVov2Vov1VSS

Charger connectionLoad connectiontIOV1(1)(4)(1)tIOV2(4)(1)tSHORT(4)(1)VM

Figure5-2 Overdischarge Current Detection

Remark: (1) Normal condition (2) Overcharge voltage condition (3) Overdischarge voltage condition (4)

Overcurrent condition

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