AAT3526 Datasheet, PDF (7/10 Pages) Advanced Analogic Technologies – MicroPower Supervisory Circuit with Manual Reset

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.
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 20kΩ
resistor, so leaving the pin unconnected is accept-
able if manual reset function is not needed. The MR
input is internally debounced which allows 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 dura-
tion 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 verses RESET comparator over-
drive. As shown in the Maximum Transient Duration
vs. Reset Threshold Overdrive graph, when the
transient voltage becomes larger, the time allowed
before asserting a reset becomes shorter. e.g. typi-
cally 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 by-pass capacitor of 0.1µF connected as
close to the V_CC pin as possible.
+3.3V
+5.0V
V_CC
AAT3528
MR
RESET
GND
100k
V_CC
RESET 5V
INPUT _System
GND
Figure 2: Using AAT3528 Open Drain Output with Multiple Supplies
3526.2002.1.0.62
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