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SLUS553D − MAY 2003 − REVISED JULY 2005
The overall accuracy of the battery charge regulation voltage is a function of the bypassed 5-V reference voltage
tolerance as well as the tolerances on R1 and R2. The precision voltage reference has a 0.5% tolerance making
it suitable for the tight battery voltage requirements of Li-ion batteries. Tolerance resistors of 0.1% are
recommended for R1 and R2 as well as any resistors used to set BATSET.
The bq24702/bq24703 provides the capability of using an internal precision voltage reference through the use
of a multiplexing scheme, refer to Figure 4, on the BATSET pin. When BATSET voltage is less than 0.25 V, an
internal reference is switched in and the BATSET pin is switched out from the g amplifier input. When the
m
BATSET voltage is greater than 0.25 V, the BATSET pin voltage is switched in to the input of the g amplifier
m
and the voltage reference is switched out.
NOTE:The minimum recommended BATSET is 1.0 V, if BATSET is used to set the voltage loop.
V
BAT
BATP
COMP
13
9
10
gm AMPLIFIER
+
BATSET
0.25 V
1.25 V
V
BAT
(a) V
BATSET
< 0.25 V
R1
BATP
COMP
VREF = 5 V
13
9
10
gm AMPLIFIER
+
R2
BATSET
0.25 V
1.196 V
UDG−00116
(b) V
BATSET
> 1 V
Figure 4. Battery Error Amplifier Input Multiplexing Scheme
19
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