ADM8690 Analog Devices, ADM8690 Datasheet - Page 14

• Manufacturer Part Number: ADM8690
• Description: µP Supervisory Circuit, 8-Pin DIP
• Manufacturer: Analog Devices

Specifications of ADM8690

• Batt-backup-flg: Yes
• Product Description: uP Supv Ckt, Watchdog Timer, Backup Battery Switching, 4.65V Reset Trip Voltage, 8-Pin DIP & SOIC
• Reset Threshold (v): 4.65
• Min Reset Timeout (ms): 35
• Reset Output-stage: Active-Low/Push-Pull
• Backup-battery Switch: Yes
• Chip Enable Gating: ---
• Typ Watchdog Timeout (ms): 100,1600
• Package: DIP,SOIC
• Us Price 1000-4999: n/a

ADM8690/ADM8691/ADM8695
POWER-FAIL WARNING COMPARATOR
An additional comparator is provided for early warning of
failure in the microprocessor power supply. The power-fail
input (PFI) is compared to an internal 1.3 V reference. The
power-fail output ( PFO ) goes low when the voltage at PFI is
less than 1.3 V.
Typically, PFI is driven by an external voltage divider that senses
either the unregulated dc input to the system 5 V regulator or
the regulated 5 V output. The voltage divider ratio can be chosen
such that the voltage at PFI falls below 1.3 V several milliseconds
before the 5 V power supply falls below the reset threshold.
Table 6. Input and Output Status in Battery Backup Mode
Signal
V
RESET
RESET
LOW LINE
BATT ON
WDI
WDO
PFI
PFO
CE
CE
OSC IN
OSC SEL
OUT
IN
OUT
Status
V
Logic low.
Logic high. The open circuit output voltage is equal to V
Logic low.
Logic high. The open circuit voltage is equal to V
WDI is ignored. It is internally disconnected from its internal pull-up resistor and does not source or sink current as long as
its input voltage is between GND and V
Logic high. The open circuit voltage is equal to V
The power-fail comparator is turned off and has no effect on the power-fail output.
Logic low.
CE
its input voltage is between GND and V
Logic high. The open circuit voltage is equal to V
OSC IN is ignored.
OSC SEL is ignored.
OUT
IN
is ignored. It is internally disconnected from its internal pull-up resistor and does not source or sink current as long as
is connected to V
BATT
via an internal PMOS switch.
OUT
OUT
. The input voltage does not affect supply current.
. The input voltage does not affect supply current.
Rev. C | Page 14 of 24
OUT
OUT
OUT
.
.
.
OUT
PFO is normally used to interrupt the microprocessor so
that data can be stored in RAM and the shutdown procedure
executed before power is lost.
.
POWER
INPUT
R1
R2
Figure 23. Power-Fail Comparator
POWER-
INPUT
FAIL
PFI
1.3V
PFO
Data Sheet
POWER-
FAIL
OUTPUT