bq24170
bq24172
SLUSAD2A –NOVEMBER 2010–REVISED NOVEMBER 2010
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DETAILED DESCRIPTION
Precharge
Current
Fastcharge Current
Regulation Phase
Fastcharge Voltage
Regulation Phase
Termination
Regulation
Phase
Regulation Voltage
VRECH
ICHRG
Charge
Current
Charge
Voltage
VLOWV
10% ICHRG
Precharge
Timer
Fast Charge Safety Timer
Figure 19. Typical Charging Profile
BATTERY VOLTAGE REGULATION
The bq24170/172 offers a high accuracy voltage regulator on for the charging voltage. The bq24170 uses CELL
pin to select number of cells with a fixed 4.2V/cell. Connecting CELL to AGND sets 1 cell output, floating CELL
pin sets 2 cell output, and connecting to VREF sets 3 cell output.
Table 2. bq24170 CELL Pin Settings
CELL PIN
AGND
VOLTAGE REGULATION
4.2V
8.4 V
12.6 V
Floating
VREF
The bq24172 uses external resistor divider for voltage feedback and regulate to internal 2.1V voltage reference
on FB pin. Use the following equation for the regulation voltage for bq24172:
R2
é
ù
V
= 2.1 V ´ 1+
BAT
ê
ú
R1
ë
û
(1)
where R2 is connected from FB to the battery and R1 is connected from FB to GND.
BATTERY CURRENT REGULATION
The ISET input sets the maximum charging current. Battery current is sensed by current sensing resistor RSR
connected between SRP and SRN. The full-scale differential voltage between SRP and SRN is 40mV max. The
equation for charge current is:
18
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