BQ2954_13 Datasheet, PDF (12/23 Pages) Texas Instruments – Lithium Ion Charge Management IC

bq2954
Charge Regulation
The bq2954 controls charging through pulse-width
modulation of the MOD output pin, supporting both
constant-current and constant-voltage regulation.
Charge current is monitored at the SNS pin, and charge
voltage is monitored at the BAT pin. These voltages are
compared to an internal reference, and the MOD output
is modulated to maintain the desired value. The maxi-
mum duty cycle is 80% .
Voltage at the SNS pin is determined by the value of re-
sistor R_SNS, so nominal regulated current is set by the
following equation:
I_MAX =V_SNS /R_SNS
(6)
The switching frequency of the MOD output is deter-
mined by an external capacitor (CPWM) between the pin
TPWM and V_SS pins, per the following:
fPWM = ^{1 ∗ 10 −4}
(7)
CPWM
Where C is in Farads and the frequency is in Hz. A
typical switching rate is 100kHz, implying CPWM =
0.001µF. MOD pulse width is modulated between 0 and
80% of the switching period.
To prevent oscillation in the voltage and current control
loops, frequency compensation networks (C and R-C
respectively) are typically required on the V_COMP and
I_COMP pins .
Recharge After Fast Charge
Once charge completion occurs, a fast charge is initiated
when the battery voltage falls below V_RECHG threshold.
A delay of approximately one second passes before re-
charge begins so that adequate time is allowed to detect
battery removal. (See Table 1.)
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