Datasheet

Sample-and-HoldCircuit
VC11
VC10
VC9
VC8
+
+
–
–
S0351-01
Differential AmpCircuit
REF=2.5V
VREF=0.975Vor1.2V
Calibration
V
OUT
0V
V – V
C(n + 1) Cn
Step 5 Vout(VREF_m)
Step6 Vout(2.5V)
VREF_m(0.975V or 1.2V)
0V
Step 1 Vd (0V)
OUT
Step 2 VREF_m
Step 2 VREF_m
Step 3 Vd (VREF_m)
OUT
Step 4 Vd (2.5V)
OUT
Kd
ACT
VREF_m(0.975V or 1.2V)
Calculate VREF_2.5V from Step 1-4
VREF_2.5V
VREF_2.5V
V
OUT
V
OUT
Calculate VREF_2.5V from Step 1–4
Differential Amp
Input
M0122-01
bq77PL900
www.ti.com ...................................................................................................................................................... SLUS844B – JUNE 2008 – REVISED JANUARY 2009
Figure 17. Cell Voltage Monitoring Circuit
To calibrate the VCELL output, it must measure a 2.5-V signal, but 2.5 V is beyond the ADC input range of most
analog-to-digital converters used in these applications. The bq77PL900 is designed to measure the 2.5 V
through a differential amplifier first, which is where the calibration procedure starts.
Figure 18. Calibration Method
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