ADM8611/ADM8612/ADM8613/ADM8614/ADM8615 Data Sheet
Rev. D | Page 12 of 17
THEORY OF OPERATION
The ADM8611/ADM8612/ADM8613/ADM8614/ADM8615
low power voltage supervisors protect the integrity of system
operation by ensuring the proper operation during power-up,
power-down, and brownout conditions. These devices monitor
the input voltage level and compare it against an internal reference.
The
RESET
output asserts whenever the monitored voltage level
is below the reference threshold, keeping the processor in a reset
state. The
RESET
output deasserts if the monitored voltage rises
above the threshold reference for a minimum period, the active
reset timeout period. This ensures that the supply voltage for
the processor is raised to an adequate level and stable before
exiting reset.
The ultralow supply current makes the ADM8611/ADM8612/
ADM8613/ADM8614/ADM8615 devices particularly suitable
for use in low power, portable equipment.
Figure 24. ADM8611 Functional Block Diagram
Figure 25. ADM8613 Functional Block Diagram
Figure 26. ADM8615 Functional Block Diagram
VOLTAGE MONITORING INPUT
The VCC pin of the ADM8611/ADM8613/ADM8614 acts as
both a device power input node and a voltage monitoring input
node. The ADM8612 uses separate pins for supply and voltage
monitoring to achieve a low voltage monitoring threshold to 0.5 V.
It is recommended to place a 0.1 μF decoupling capacitor as close
as possible to the device between the VCC pin and the GND pin.
VIN AS AN ADJUSTABLE INPUT
Due to the low leakage nature of the VIN pin, the ADM8612 or
ADM8615 can be used as devices with an adjustable threshold. Use
an external resistor divider circuit to program the desired voltage
monitoring threshold based on the VIN threshold, as shown in
Figure 27.
Figure 27. ADM8615 Typical Application Circuit
TRANSIENT IMMUNITY
To avoid unnecessary resets caused by fast power supply transients,
an input glitch filter is added to the VCC pin of the ADM8611/
ADM8613/ADM8614 and the VIN pin of the ADM8612 and
ADM8615 to filter out the transient glitches on these pins.
Figure 16 shows the comparator overdrive (that is, the maximum
magnitude of negative going pulses with respect to the typical
threshold) vs. the pulse duration without a reset.
RESET OUTPUT
The ADM8611/ADM8612/ADM8613/ADM8614/ADM8615
devices all have an active low, open-drain reset output. For the
ADM8611/ADM8613/ADM8614, the state of the output is
guaranteed to be valid as soon as V
CC
is greater than 0.9 V. For
the ADM8612 and ADM8615, the output is guaranteed to be
held low from when V
CC
= 0.9 V to when the device exits ULVO.
When the monitored voltage falls below its associated threshold,
RESET
is asserted within 23 μs to 26 μs (typical). Asserting
RESET
this quickly ensures that the entire system can be reset at once
before any part of the system voltage falls below its recommended
operating voltage. This system reset can avoid dangerous and/or
erroneous operation of a microprocessor-based system.
MR
GND
ADM8611
RESET
GENERATOR
DEBOUNCE
RESET
CC
V
TH
12782-024
GND
WD_DISWDI
CC
V
TH
ADM8613
RESET
GENERATOR
RESET
WATCHDOG
DETECTOR
MR
DEBOUNCE
12782-025
GND
WDI
CC
VIN
V
TH
ADM8615
RESET
GENERATOR
RESET
WATCHDOG
DETECTOR
MR
DEBOUNCE
12782-026
ADM8615
MICROPROCESSOR
VCC
VIN
GND
RESET RESET
MR
WDI OUTPUT
3.3
12V
V
IO
12782-127