BQ2000T_15 Datasheet, PDF (11/29 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

bq2000T
www.ti.com
SLUS149D – MAY 1999 – REVISED JANUARY 2010
Table 2. RC Pin Status (continued)
bq2000T CHARGE STATE
Fast charge (current and voltage regulation)
Top-off charge
Trickle maintenance charge (after fast charge)
Charge complete
TS PIN STATE
RC PIN BEHAVIOR
V_TS < V_LTF
V_TS > V_LTF (in battery conditioning state)
V_TS > V_LTF (in trickle maintenance charge
state)
V_LTF > V_TS > V_HTF
V_HTF > V_TS > V_TCO
Active
1-V to 2-V DC level (timer is paused and
resumes when V_TS < V_LTF)
1-V to 2-V DC level (timer is paused and
resumes when V_TS < V_LTF)
Active
Active (timer is still counting, even though
charging is suspended)
N/A
1-V to 2-V DC level
N/A
Active
Both top-off and trickle maintenance charge are terminated and the pack never receives any more charge (until a
charge initialization occurs) if the voltage on the BAT pin reaches V_MCV. During trickle maintenance charge,
charging is suspended if V_TS < V_HTF. It resumes when V_TS > V_HTF. The bq2000T is designed to remain in trickle
maintenance charge forever (excluding the two faults just mentioned) in order to keep a Nickel pack full.
Charge Current Control
The bq2000T implements a hysteretic control loop that regulates the current being delivered to the battery pack
to a user programmable value that is set by the value of the R_SNS resistor. A second, outer control loop reduces
the average current delivered to the pack in order to clamp the voltage at the BAT pin to a maximum of V_MCV.
The bq2000T controls the MOD pin to regulate the current and voltage of the pack. The bq2000T monitors
charge current at the SNS input by sensing the voltage drop across a sense-resistor, R_SNS, in series with the
battery pack. See Figure 8 for a typical current-sensing circuit.
BAT-
R_f
R_SNS
1 _SNS
Cf
2 _VSS
Power Supply ground
bq2000T ground and BAT-
bq2000T
Figure 8. Current-Sensing Circuit
R_SNS is sized to provide the desired fast-charge current (I_MAX).
0.05
I_MAX
=
R_SNS
(3)
If the voltage at the SNS pin is greater than V_SNSLO or less than V_SNSHI, the bq2000T switches the MOD output
high to pass charge current to the battery. When the SNS voltage is less than V_SNSLO or greater than V_SNSHI, the
bq2000T switches the MOD output low to shut off charging current to the battery. A hysteresis capacitor (C_HYS) is
required between the C_MOD pin and the SNS pin to add a healthy amount of hysteresis to the current sense
signal. Typical hysteresis values are between 5 mV and 25 mV. The amount of hysteresis can be calculated by
examining the capacitive divider formed by C_HYS and C_f.
Hysteresis (V) = VCC
´
CHYS
(CHYS + Cf )
(4)
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