BQ24620 Datasheet, PDF (14/30 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Lithium Phosphate Battery Charger with Low Iq

bq24620
SLUS893 – MARCH 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 11. Typical Charging Profile
BATTERY VOLTAGE REGULATION
The bq24620 uses a high accuracy voltage bandgap and regulator for the 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
+
R2
R1
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 charging current. Battery 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_ISET
20 ´ R_SR
(2)
V_ISET, The input voltage range of ISET 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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