Applications Formulae and Typical Values
VCC
RP
9V
9.1m½
Program and Standby Currents: IP =
=
Å 1µA Standby Current = 4IP = 4µA (typ.)
VTCT 7CT
7 x 4.7µF
1µA
Cycle Timer Period: Tt =
=
=
Å 33sec.,
IP
1µA
where Vt = Upper Charge Threshold - Lower Charge Threshold (7V typ.)
Test Pulse Width: Tp = RdCT x ln(VP) Å 242CTÅ 242 x 4.7µF Å 1.14ms
where Rd is the dynamic cycle timer discharge impedance (440½ typ.)
Upper Charge Threshold
Lower Discharge Threshold
[1n(VP) = 0.55 typ.]
and VP =
2.5 x 0.1µF
250µA
VdCPW 2.5CPW
Pulse Stretcher: Delay Time: TD =
=
=
Å 1ms
Isrc
250µA
where Vd = Schmitt Trigger Upper Threshold (2.5V typ.)
and Isrc = Typical source current at the PW pin at the nominal low battery sense threshold of 6.7V.
Pulse Width: Tp = CPWRPW ln(VS) Å 0.51 x 0.1µF x 10m½ Å 510ms.
Schmitt Trigger Upper Threshold
and VS =
[ln(VS) = 0.51 typ.]
Schmitt Trigger Hysteresis
Applications Information
The value of Rp affects standby current, operating current,
and the test cycle period. The recommended value is
(V+/1µA) where V+ is the fresh battery voltage. Higher
values of Rp are not recommended. Minimum recom-
mended value is (V+/10µA) which will increase both the
standby and operating currents by 10X and reduce the test
cycle period by the same factor; the test pulse width will
be unaffected.
The pulse stretcher components RPW and CPW should be
selected such that the delay timer to charge CPW is shorter
than the test pulse width programmed by Ct to guarantee
operation of the Output. The output is an open-collector
transistor which may be used to drive an indicator device
directly or to interface to logic family devices.
The SENSE input typical 8.5k½ input impedance appears
only during the test pulse; otherwise the SENSE input is in
a high impedance state. The effective low battery thresh-
old voltage can be modified (increased only) by means of a
voltage divider placed across the load resistor. This tech-
nique can also be used to effectively reduce the threshold
tolerance band.
The value of Ct affects both the test cycle period and the
test pulse width. Of critical importance is the selection of a
low leakage type capacitor; if leakage current exceeds the
cycle timer charge current, the timer will not operate.
Typical Application Circuit
R
p
V
CC
R
p
V
CC
9.1MW
C
pw
0.1mF
SENSE
PW
R
pw
CS2516
10MW
510W
C
T
+
C
T
OUT
4.7mF
COM
Load Switch
220W
+
9V
4
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
