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AAT3526/7/8

MicroPower Supervisory Circuit

with Manual Reset

Applications Information

Reset Output Options

The AAT3528 has an active low open drain outputand the AAT3526/7 have a push-pull output. TheAAT3528 may be used in multiple voltage systemswith an external pull-up resistor. This allows theAAT3528 to interface to microprocessors with high-er supply voltages up to 5.5V (Figure 2). In the eventof a power-down or brown-out condition, the resetsignal remains valid until the VCCdrops below 1.2V.To ensure validity down to ground, an external100k resistor should be connected between theRESEToutput and GND.

use of a mechanical switch. It should be a normally-GND. Additionally, the MR pin can be driven fromTTL, CMOS, or open drain logic outputs.

Supply Voltage Transient Behavior

In some cases, fast negative transients of shortduration can appear on the VCCpower supply. TheAAT3526/7/8 series devices provide some immunityto line transients which can generate invalid resetpulses. Figure 1 shows typical behavior to shortduration pulses versus RESETcomparator over-drive. As shown in the Maximum Transient Durationvs. Reset Threshold Overdrive graph, when the tran-sient voltage becomes larger, the time allowedbefore asserting a reset becomes shorter (e.g., typ-ically a transient of 100mV below the reset thresholdwould have to present for more than 50µs to causea reset). Immunity can be increased by the additionof a small bypass capacitor of 0.1µF connected asclose to the VCCpin as possible.

Manual Reset Input

Ais lowThis input is internally pulled up to VCCvia a 65k resistor, so leaving the pin unconnected is accept-able if the manual reset function is not needed. The

3526.2006.03.1.6

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