Datasheet

BATTERY MONITORING
R =R
1
F
=20MW
V
HYST
V
BATT
=420kW
50mV
2.4V
(2)
R =
2
-
V
THRS
V
1
REF
R
´
1
R
1
1
(
)
-
1
R
F
=
-
2V
1.2V 420kW
´
1
420kW
1
( )
-
1
20MW
= 650kW
(3)
R =
F
V
REF
1000(I
BMAX
)
=
1.2V
1000(50pA)
= 24M 20MW W»
(1)
R =
BIAS
=0.3MW
(V
BATTMIN
- V )
REF
I
BIAS
=
( 1.2V)-1.8V
2 Am
(4)
REF1112
OPA369
+IN
OUT
-IN
V
STATUS
V
BATT
V
REF
R
1
R
2
R
BIAS
I
BIAS
R
F
+
OPA369
OPA2369
SBOS414B – AUGUST 2007 – REVISED DECEMBER 2008 ............................................................................................................................................ www.ti.com
The low operating voltage and quiescent current of
the OPA369 series make it an excellent choice for
4. Select a threshold voltage for V
IN
rising (V
THRS
) =
battery monitoring applications, as shown in
2.0V
Figure 25 . In this circuit, V
STATUS
is high as long as
5. Calculate R
2
as follows:
the battery voltage remains above 2V. A low-power
reference is used to set the trip point. Resistor values
are selected as follows:
1. Selecting R
F
: Select R
F
such that the current
through R
F
is approximately 1000x larger than
the maximum bias current over temperature:
6. Calculate R
BIAS
: The minimum supply voltage for
this circuit is 1.8V. The REF1112 has a current
requirement of 1.2 µ A (max). Providing the
2. Choose the hysteresis voltage, V
HYST
. For
REF1112 with 2 µ A of supply current assures
battery-monitoring applications, 50mV is
proper operation. Therefore:
adequate.
3. Calculate R
1
as follows:
Figure 25. Battery Monitor
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