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When the battery voltage becomes higher

during charging under normal condition

and the state continues for the overcharge

HM9901 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

HM9901 turns the charging control FET

on and returns to the normal condition.

2, When a load is connected and

discharging starts, the HM9901 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

HM9901 detects this voltage and

releases the overcharge condition.

Consequently, in the case that the battery

voltage is equal to or lower than the

HM9901 returns to the normal condition

immediately, but in the case the battery

voltage is higher than the overcharge

return to the normal condition until the

battery voltage drops below the overcharge

connected. In addition, if the VM pin

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

the battery voltage does not drops below the

heavy load, which causes an overcurrent, is

connected, the overcurrent do not work until the

battery voltage drops below the overcharge

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.

Overdischarge Condition

When the battery voltage drops below the

during discharging under normal condition

and it continues for the overdischarge

HM9901 turns the discharging control

FET off and stops discharging. This

condition is called overdischarge condition.

After the discharging control FET is turned

resistor

between VM and VDD in HM9901.

Meanwhile when VM is bigger than 1.5

V (typ.) (the load short-circuiting detection

voltage), the current of the chip is reduced

condition is called power-down condition.

The VM and VDD pins are shorted by 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

the HM9901 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

under overdischarge condition is connected to a

charger, the overdischarge condition is released

HM9901