HM9902A datasheet(5/11 Pages) HMSEMI

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HM9902A

overcharge detection voltage (VCU) even when a

heavy load, which causes an overcurrent, is

connected, the overcurrent 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 work. Detection of load

short-circuiting works regardless of the battery

voltage.

When the battery voltage becomes higher

than the overcharge detection voltage (VCU)

during charging under normal condition and

the state continues for the overcharge

detection delay time (tCU) or longer, the

HM9902A turns the charging control FET

off 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

HM9902A turns the charging control FET

on and returns to the normal condition.

2, When a load is connected and

discharging starts, the HM9902A 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

HM9902A 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 HM9902A returns 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

voltage is equal to or lower than the

overcurrent 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

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

HM9902A 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 HM9902A.

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 HM9902A 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

- 5 -

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