Datasheet

ADM6326/ADM6328/ADM6346/ADM6348
Rev. 0 | Page 7 of 12
THEORY OF OPERATION
The ADM6326/ADM6328/ADM6346/ADM6348 are designed
to protect the integrity of a system’s operation by ensuring the
proper operation of the system during power-up, power-down,
and brownout conditions. Ultralow supply currents make these
devices particularly suitable for use in low power, portable
equipment.
RESET OUTPUT
The ADM6326 and ADM6346 have an active low, push-pull
reset output, whereas the ADM6328 and ADM6348 have an
active low, open-drain reset output, which requires an external
pull-up resistor. The
RESET
signal is guaranteed to be valid for
V
CC
down to 1 V.
When the ADM6326/ADM6328/ADM6346/ADM6348 are
powered up, the
RESET
output remains low for a period typically
equal to the
RESET
active timeout period of 185 ms. This feature
allows adequate time for the system to power up correctly and
for the power supply to stabilize before any devices are brought out
of reset and are allowed to begin executing instructions. Initializing
a system in this way provides a more reliable startup for micro-
processor systems.
When the monitored voltage falls below its associated threshold
(V
TH
),
RESET
is asserted within 20 μs (typical). Asserting
RESET
this quickly means that the entire system can be reset at once
before any part of the system’s voltage falls below its recommended
operating voltage. This system reset can avoid dangerous and/or
erroneous operation of a microprocessor based system.
INTERFACING TO OTHER DEVICES
The active low, open-drain reset output of the ADM6328 and
ADM6348 makes these devices ideal for integration with devices
such as microprocessors with bidirectional reset pins. Simply
connect the
RESET
output of the ADM6328 or ADM6348 to
the
RESET
input of the microprocessor using a single pull-up
resistor to allow either device to initiate a system reset (see
). Figure 8
08052-008
ADM6328/ADM6348
V
CC
V
CC
GND
RESET
MICROPROCESSOR
SYSTEM
V
CC
GND
R
PULL-UP
RESET
INPUT
Figure 8. Interfacing to a Microprocessor with a Bidirectional Reset Pin
TRANSIENT IMMUNITY
To avoid unnecessary resets caused by fast power supply transients,
the ADM6326/ADM6328/ADM6346/ADM6348 provide glitch
immunity from negative-going V
CC
transients.
Figure 5 shows the
RESET
comparator overdrive (that is, the
maximum magnitude of negative-going pulses with respect to
the typical threshold) vs. the pulse duration without a reset.
0
8052-009
V
CC
V
CC
V
TH
V
TH
t
RD
t
RP
V
CC
0V
0V
1V
RESET
Figure 9.
RESET
Timing