ous operational states and their associated conditions

which are described in detail in the following section.

Figure 3 is an application example.

Charge Initiation

The bq2902 always initiates and performs a charge cycle

whenever a valid DC input is applied. A charge cycle

consists of pulse charging the battery and then checking

for a termination condition.

The charging section ex-

plains charging in greater detail.

Charge Pre-Qualification

After DC is applied, the bq2902 checks the open-circuit

dicates a fault condition (see Table 1). The bq2902 re-

Charge Termination

Once a charge cycle begins, the bq2902 terminates

charge when the average charge rate falls below 3% of

the maximum charge rate. The bq2902 also terminates

condition on the CHG output (see Table 1).

Charge Re-Initiation

If DC remains valid, the bq2902 suspends all charge

activity after full-charge termination. A charge cycle is

re-initiated when all cell potentials fall below 1.4V. The

rechargeable alkaline cells, unlike other rechargeable

chemistries, do not require a maintenance charge to

keep the cells in a fully charged state. The self-discharge

rate for the Renewal cells is typically 4% per year at

room temperature.

Charge Status Indication

Table 1 and Figure 2 outline the various charge action

states. The charge status output is designed to work

with an LED indicator. In all cases, if DC is not present

at the DC pin, or if the DC supply is less than the volt-

impedance condition.

Charging

The bq2902 controls charging by periodically connecting

the DC current-source to the battery stack, not to the in-

dividual battery cells.

The charge current is pulsed

from the internal clock at approximately a 80Hz rate on

The bq2902 pulse charges the battery for approximately

10ms of every 12.5ms, when conditions warrant. The

battery cell during the idle period. If a single-cell poten-

3

bq2902

Charge Action State

Conditions

CHG

Output

DC absent

Z

Charge initiation

DC applied

-

-

Charge pending/

fault

-

2

2

Charge pulse

≤ 1.63V before pulse

Charge pulsed @ 80Hz per Figure 2

1

1

Pulse skip

before pulse

Pulse skipped per Figure 2

1

1

Charge complete

Average charge rate falls below 3% of

the fast charge rate

Charge complete

Low

Notes:

1.

2.

Table 1. bq2902 Operational Summary