Datasheet
R =
F
V
REF
1000(I )
BMAX
=
1.2V
1000(100pA)
=12M 10M» WW
(1)
R =R
1
F
V
HYST
V
BATT
=10MW
50mW
2.4V
=210kW
(2)
R
IN
OPA379
V
IN
V
OUT
R
F
C
FB
C
IN
BATTERY MONITORING
R =
2
1
-
V
THRS
V R´
REF 1
1
R
1
-
1
R
F
=
1
-
2V
1.2V ´ 210kW
1
210kW
-
1
10MW
=325kW
(3)
R =
BIAS
(V V )-
REFBATTMIN
I
BIAS
=
(1.8V 1.2V)-
2 Am
=0.3MW
(4)
REF1112
OPA379
+IN
OUT
-IN
V
STATUS
V
BATT
V
REF
R
1
R
2
R
BIAS
I
BIAS
R
F
+
OPA379
OPA2379
OPA4379
SBOS347D – NOVEMBER 2005 – REVISED MAY 2008 ...................................................................................................................................................
www.ti.com
In unity-gain inverter configuration, phase margin can
be reduced by the reaction between the capacitance
at the op amp input and the gain setting resistors.
Best performance is achieved by using smaller
valued resistors. However, when large valued
resistors cannot be avoided, a small (4pF to 6pF)
capacitor, C
FB
, can be inserted in the feedback, as
shown in Figure 22 . This configuration significantly 2. Choose the hysteresis voltage, V
HYST
. For battery
reduces overshoot by compensating the effect of monitoring applications, 50mV is adequate.
capacitance, C
IN
, which includes the amplifier input
3. Calculate R
1
as follows:
capacitance (3pf) and printed circuit board (PC)
parasitic capacitance.
4. Select a threshold voltage for V
IN
rising (V
THRS
) =
2.0V
5. Calculate R
2
as follows:
Figure 22. Improving Stability for Large R
F
and R
IN
The low operating voltage and quiescent current of
6. Calculate R
BIAS
: The minimum supply voltage for
the OPA379 series make it an excellent choice for
this circuit is 1.8V. The REF1112 has a current
battery monitoring applications, as shown in
requirement of 1.2 µ A (max). Providing 2 µ A of
Figure 23 . In this circuit, V
STATUS
is high as long as
supply current assures proper operation.
the battery voltage remains above 2V. A low-power
Therefore:
reference is used to set the trip point. Resistor values
are selected as follows:
1. R
F
Selecting: Select R
F
such that the current
through R
F
is approximately 1000x larger than
the maximum bias current over temperature:
Figure 23. Battery Monitor
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