BQ24630 Datasheet, PDF (14/33 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Lithium Phosphate Battery Charger with System Power Selector and Low Iq

bq24630
SLUS894 – JANUARY 2010
Regulation Voltage
V_RECH
Regulation Current
Precharge
Current
Regulation
Phase
DETAILED DESCRIPTION
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Charge
Current
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Termination
V_LOWV
I_PRECH & I_TERM
Charge
Voltage
Precharge
Time
Fastcharge Safety Time
Figure 17. Typical Charging Profile
BATTERY VOLTAGE REGULATION
The bq24630 uses a high accuracy voltage bandgap and regulator for the high accuracy charging voltage. The
charge voltage is programmed via a resistor divider from the battery to ground, with the midpoint tied to the VFB
pin. The voltage at the VFB pin is regulated to 1.8V, giving Equation 1 for the regulation voltage:
V_BAT = 1.8 V ´
é
êë¹
+
R1
R2
ù
úû
(1)
where R2 is connected from VFB to the battery and R1 is connected from VFB to GND
BATTERY CURRENT REGULATION
The ISET1 input sets the maximum fast charging current. Battery charge current is sensed by resistor R_SR
connected between SRP and SRN. The full-scale differential voltage between SRP and SRN is 100mV. Thus, for
a 10mΩ sense resistor, the maximum charging current is 10A. Equation 2 is for charge current
I_CHARGE =
V_ISET1
20 ´ R_SR
(2)
V_ISET1, the input voltage range of ISET1 is between 0 and 2V. The SRP and SRN pins are used to sense voltage
across R_SR with default value of 10mΩ. However, resistors of other values can also be used. A larger sense
resistor will give a larger sense voltage, a higher regulation accuracy; but, at the expense of higher conduction
loss.
14
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