with a trickle maintenance-charge that continues as

Lithium-Ion Batteries

The bq2000T uses a two-phase fast-charge algorithm for

Li-Ion batteries (Figure 3). In phase one, the bq2000T

bq2000T then moves to phase two, regulates the battery

charge cycle is started if the cell voltage falls below the

During the current-regulation phase, the bq2000T

monitors charge time, battery temperature, and battery

voltage for adherence to the termination criteria. During

the final constant-voltage stage, in addition to the

charge time and temperature, it monitors the charge

current as a termination criterion. There is no

post-charge maintenance mode for Li-Ion batteries.

Charge Termination

Maximum Charge Time (NiCD, NiMH, and

Li-Ion)

The bq2000T sets the maximum charge-time through

pin RC. With the proper selection of external resistor

and capacitor, various time-out values may be achieved.

Figure 4 shows a typical connection.

The following equation shows the relationship between

time (MTO) for the bq2000T:

other features of the device. See Tables 2 and 3 for de-

tails.)

For Li-Ion cells, the bq2000T resets the MTO when the

battery reaches the constant-voltage phase of the

charge. This feature provides the additional charge time

required for Li-Ion cells.

Maximum Temperature (NiCd, NiMH, Li-Ion)

placed in thermal contact with the battery, may be used

as a temperature-sensing device. Figure 5 shows a typi-

cal temperature-sensing circuit.

During fast charge, the bq2000T compares the battery

temperature to an internal high-temperature cutoff

termination occurs when voltage at pin TS is less than

this threshold.

∆T/∆t (NiCd, NiMH)

When fast charging, the bq2000T monitors the voltage

at pin TS for rate of temperature change detection,

∆T/∆t. The bq2000T samples the voltage at the TS pin

every 16s and compares it to the value measured 2 sam-

ples earlier. This feature terminates fast charge if this

voltage declines at a rate of

V

161

V

Min

CC









Figure 5 shows a typical connection diagram.

Minimum Current (Li-Ion Only)

The bq2000T monitors the charging current during the

voltage-regulation phase of Li-Ion batteries. Fast charge

is terminated when the current is tapered off to 7% of

the maximum charging current. Please note that this

threshold is different for the bq2000.

Initial Hold-Off Period

The values of the external resistor and capacitor con-

nected to pin RC set the initial hold-off period. During

this period, the bq2000T avoids early termination by

disabling the

∆T/∆t feature. This period is fixed at the

5

Battery Chemistry

Charge Algorithm

NiCd or NiMH

1. Charge qualification

2. Trickle charge, if required

3. Fast charge (constant current)

4. Charge termination (

∆T/∆t, time)

5. Top-off (optional)

6. Trickle charge

Li-Ion

1. Charge qualification

2. Trickle charge, if required

3. Two-step fast charge (constant current followed by constant voltage)

4. Charge termination (minimum current, time)

Table 1. Charge Algorithm

bq2000T