BQ2005 Datasheet, PDF (5/16 Pages) Texas Instruments – Fast-Charge IC for Dual-Battery Packs

bq2005
Table 1. Fast Charge Safety Time/Hold-Off/Top-Off Table
Corresponding
Fast-Charge Rate
C/4
C/2
1C
2C
4C
C/2
1C
2C
4C
TM1
Low
Float
High
Low
Float
High
Low
Float
High
TM2
Low
Low
Low
Float
Float
Float
High
High
High
Typical Fast-Charge
and Top-Off
Time Limits
360
180
90
45
23
180
90
45
23
Typical -∆V/MCV
Hold-Off
Time (seconds)
137
820
410
200
100
820
410
200
100
Note:
Typical conditions = 25°C, VCC = 5.0V.
Top-Off
Rate
Disabled
Disabled
Disabled
Disabled
Disabled
C/16
C/8
C/4
C/2
-∆V Termination
If the DVEN input is high, the bq2005 samples the volt-
age at the BAT pin once every 34s. If VCELL is lower
than any previously measured value by 12mV ±4mV,
fast charge is terminated. The -∆V test is valid in the
range VMCV - (0.2 ∗ VCC) < VCELL < VMCV.
Voltage Sampling
Each sample is an average of 16 voltage measurements
taken 57µs apart. The resulting sample period
(18.18ms) filters out harmonics around 55Hz. This tech-
nique minimizes the effect of any AC line ripple that
may feed through the power supply from either 50Hz or
60Hz AC sources. Tolerance on all timing is ±16%.
Voltage Termination Hold-off
A hold-off period occurs at the start of fast charging.
During the hold-off period, -∆V termination is disabled.
This avoids premature termination on the voltage spikes
sometimes produced by older batteries when fast-charge
current is first applied. ∆T/∆t, maximum voltage and
maximum temperature terminations are not affected by
the hold-off period.
∆T/∆t Termination
The bq2005 samples at the voltage at the TS pin every
34s, and compares it to the value measured two samples
earlier. If VTEMP has fallen 16mV ±4mV or more, fast
charge is terminated. The ∆T/∆t termination test is
valid only when VTCO < VTEMP < VLTF.
Temperature Sampling
Each sample is an average of 16 voltage measurements
taken 57µs apart. The resulting sample period
(18.18ms) filters out harmonics around 55Hz. This tech-
nique minimizes the effect of any AC line ripple that
may feed through the power supply from either 50Hz or
60Hz AC sources. Tolerance on all timing is ±16%.
Maximum Voltage, Temperature, and Time
Anytime VCELL rises above VMCV, CHG goes high (the LED
goes off) immediately. If the bq2005 is not in the voltage
hold-off period, fast charging also ceases immediately. If
VCELL then falls back below VMCV before tMCV = 1s
(maximum), the chip transitions to the Charge Complete
state (maximum voltage termination). If VCELL remains
above VMCV at the expiration of tMCV, the bq2005 transi-
tions to the Battery Absent state (battery removal). See
Figure 4.
Maximum temperature termination occurs anytime the
voltage on the TS pin falls below the temperature cut-off
threshold VTCO. Charge will also be terminated if VTEMP
rises above the minimum temperature fault threshold,
VLTF, after fast charge begins.
Maximum charge time is configured using the TM pin.
Time settings are available for corresponding charge
rates of C/4, C/2, 1C, and 2C. Maximum time-out termi-
nation is enforced on the fast-charge phase, then reset,
and enforced again on the top-off phase, if selected.
There is no time limit on the trickle-charge phase.
Top-off Charge
An optional top-off charge phase may be selected to
follow fast charge termination for the C/2 through 4C
rates. This phase may be necessary on NiMH or other
5