ADM8696ARW Analog Devices Inc, ADM8696ARW Datasheet - Page 9

• Manufacturer Part Number: ADM8696ARW
• Description: IMPROVED ADM696 I.C.
• Manufacturer: Analog Devices Inc
• Type: Battery Backup Circuitr

Specifications of ADM8696ARW

• Rohs Compliant: NO
• Rohs Status: RoHS non-compliant
• Number Of Voltages Monitored: 1
• Output: Push-Pull, Push-Pull
• Reset: Active High/Active Low
• Reset Timeout: 35 ms Minimum
• Voltage - Threshold: 1.3V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.300", 7.5mm Width)

REV. A
APPLICATIONS INFORMATION
Increasing the Drive Current (ADM8696)
If the continuous output current requirements at V
100 mA or if a lower V
an external PNP pass transistor may be connected in parallel
with the internal transistor. The BATT ON output (ADM8696)
can directly drive the base of the external transistor.
Using a Rechargeable Battery for Backup (ADM8696)
If a capacitor or a rechargeable battery is used for backup, the
charging resistor should be connected to V
nates the discharge path that would exist during power-down if
the resistor is connected to V
Adding Hysteresis to the Power Fail Comparator
For increased noise immunity, hysteresis may be added to the
power fail comparator. Since the comparator circuit is nonin-
verting, hysteresis can be added by connecting a resistor be-
tween the PFO output and the PFI input as shown in Fig-
ure 16. When PFO is low, resistor R3 sinks current from the
summing junction at the PFI pin. When PFO is high, the series
combination of R3 and R4 source current into the PFI summing
junction. This results in differing trip levels for the comparator.
Alternate Watchdog Input Drive Circuits
The watchdog feature can be enabled and disabled under pro-
gram control by driving WDI with a three-state buffer (Figure
17a). When three-stated, the WDI input will float, thereby dis-
abling the watchdog timer.
POWER
POWER
INPUT
INPUT
+5V
+5V
BATTERY
RECHARGABLE
Figure 14. Increasing the Drive Current
0.1 F
Figure 15. Rechargeable Battery
BATTERY
0.1 F
CC
–V
V
BATT
OUT
V
V
CC
BATT
CC
V
ADM8696
.
TRANSISTOR
CC
voltage differential is desired,
I =
ADM8696
BATT
V
PNP
ON
OUT
R
– V
R
BATT
V
OUT
OUT
V
OUT
since this elimi-
0.1 F
0.1 F
OUT
exceeds
–9–
This circuit is not entirely foolproof and it is possible a software
fault could erroneously three-state the buffer. This would pre-
vent the ADM869x from detecting that the microprocessor is no
longer operating correctly. In most cases, a better method is to
extend the watchdog period rather than disabling the watchdog.
This may be done under program control using the circuit
shown in Figure 17b. When the control input is high, the OSC
SEL pin is low and the watchdog timeout is set by the external
capacitor. A 0.01 F capacitor sets a watchdog timeout delay of
100 s. When the control input is low, the OSC SEL pin is
driven high, selecting the internal oscillator. The 100 ms or the
1.6 s period is chosen, depending on which diode in Fig-
ure 17b is used. With D1 inserted, the internal timeout is set at
100 ms while with D2 inserted the timeout is set at 1.6 s.
Figure 16. Adding Hysteresis to the Power Fail Comparator
+7V TO +15V
WATCHDOG
Figure 17a. Programming the Watchdog Input
Figure 17b. Programming the Watchdog Input
POWER
CONTROL
CONTROL
INPUT
STROBE
INPUT
INPUT*
R1
R2
V
V
ASSUMING R
HYSTERESIS V
H
L
= 1.3V
= 1.3V
D1
7805
(
(
1+ ––– – –––––––––––––
1+ ––– + –––
4 < <
R
R
R
R
H
1
2
1
2
– V
+5V
PFI
R
D2
ADM8696/ADM8697
3
R
L
R
R
1.3V (R
THEN
1
= 5V
1
3
*LOW = INTERNAL TIMEOUT
HIGH = EXTERNAL TIMEOUT
1.3V
(5V – 1.3V)
)
ADM869x
(
3 +
–––
V
R
R
OSC IN
OSC SEL
CC
WDI
1
2
R
4
)
)
)
R3
ADM869x
ADM869x
PFO
R4
TO
P NMI