AAT3526/7/8
MicroPower™ Supervisory Circuit
with Manual Reset
Applications Information
Reset Output Options
The AAT3528 has an active low open drain output
and the AAT3526/7 have a push-pull output. The
AAT3528 may be used in multiple voltage systems
with an external pull-up resistor. This allows the
AAT3528 to interface to microprocessors with high-
er supply voltages up to 5.5V (Figure 2). In the event
of a power-down or brown-out condition, the reset
signal remains valid until the V
CC
drops below 1.2V.
To ensure validity down to ground, an external
100kΩ resistor should be connected between the
RESET output and GND.
MR input is internally debounced which allows the
use of a mechanical switch. It should be a normally-
open momentary switch connected from MR to
GND. Additionally, the MR pin can be driven from
TTL, CMOS, or open drain logic outputs.
Supply Voltage Transient Behavior
In some cases, fast negative transients of short
duration can appear on the V
CC
power supply. The
AAT3526/7/8 series devices provide some immunity
to line transients which can generate invalid reset
pulses. Figure 1 shows typical behavior to short
duration pulses versus RESET comparator over-
drive. As shown in the Maximum Transient Duration
vs. Reset Threshold Overdrive graph, when the tran-
sient voltage becomes larger, the time allowed
before asserting a reset becomes shorter (e.g., typ-
ically a transient of 100mV below the reset threshold
would have to present for more than 50µs to cause
a reset). Immunity can be increased by the addition
of a small bypass capacitor of 0.1µF connected as
close to the V
CC
pin as possible.
Manual Reset Input
A logic low signal on MR asserts a reset condition.
Reset continues to be asserted as long as MR is low
and for a minimum of 150ms after MR returns high.
This input is internally pulled up to V
CC
via a 65kΩ
resistor, so leaving the pin unconnected is accept-
able if the manual reset function is not needed. The
V
CC
VCC
*
100k
(nominal)
VCC
0.1µF
MR
AAT3526
AAT3527
RESET
(RESET)
AAT3528
RESET
µP
INPUT
GND
GND
*AAT3528 Only
Figure 2: Using Recommended Bypass Capacitor.
+3.3V
+5.0V
VCC
100k
VCC
AAT3528
MR
RESET
RESET
INPUT
5V
System
GND
GND
Figure 3: Using AAT3528 Open Drain Output with Multiple Supplies.
3526.2006.03.1.6
7
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
