AS1925 datasheet(9/12 Pages) AMSCO

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AS1925/AS1926

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

Interfacing to Bi-Directional Microprocessor Reset Pins

Because the RESETN output of the AS1926 is open drain, this device interfaces easily with microprocessors that have

bidirectional reset pins. Connecting the AS1926 RESETN output directly to the microprocessor RESETN pin with a

single pullup resistor allows either device to assert reset (Figure 11 on page 9).

Figure 11. Interfacing to Microprocessors with Bidirectional Reset Pins

Using the AS1926 Open-Drain RESETN Output with Multiple Supplies

In a typical application, the pullup resistor connected to the AS1926 connects to the voltage being monitored at pin

VCC. However, some systems use an open-drain output to level-shift from the monitored supply to reset circuitry pow-

ered by another supply (see Figure 12).

As VCC decreases, so does the ability of the AS1926 to sink current at RESETN. RESETN is pulled high as VCC

decreases toward 0V. The voltage where this occurs depends on the value of the pullup resistor and the supply voltage

to which it is connected.

Figure 12. AS1926 Open-Drain RESETN Output with Multiple Supplies

AS1926

CPU

VCC

GND

VCC

RESETN

GND

VCC

RESETN

+0.9V

AS1926

CPU

GND

+5.0V

RESETN

VCC

RPULLUP

GND

VCC

RESETN

AS1925 Fiches technique(PDF) 9 Page - ams AG