IMP1817 datasheet(18/36 Pages) A1PROS

18 / 36 page

408-432-9100/www.impweb.com

1999 IMP, Inc.

IMP1

IMP1881155

Application Information

Operation – Power Monitor

The IMP1815 detects out-of-tolerance power supply conditions. It

resets a processor during power-up, power-down and issues a

reset to the system processor when the monitored power supply

voltage is below the reset threshold. When an out-of-tolerance VCC

voltage is detected, the RESET signal is asserted. On power-up,

RESET is kept active (LOW) for approximately 150ms after the

power supply voltage has reached the selected tolerance. This

allows the power supply and microprocessor to stabilize before

RESET is released.

Output Conditions

The IMP1815 active LOW reset signal is valid as long as VCC

remains above 1.2V. The RESET output on the IMP1815 uses a

push-pull drive stage that can maintain a valid output below 1.2V.

To sink current with VCC below 1.2V, a resistor can be connected

from the reset pin (RESET) to Ground (see Figure 1). This

configuration will give a valid value on the RESET output with

VCC approaching 0V. During both power up and down, this con-

figuration will draw current when RESET is in the high state. A

value of 100k

Ω should be adequate to maintain a valid condition.

IMP1815

Microprocessor

RESET

100k

RESET

1815_06.eps

Figure 1. RESET Valid to 0V VCC

Figure 2. Timing Diagram: Power-Up

Figure 3. Timing Diagram: Power-Down

VCCTP (MAX)

VCCTP

VCCTP (MIN)

VCC

RESET

tRPU

VOH

1815_07.eps

VCCTP (MAX)

VCCTP

VCCTP (MIN)

VCC

RESET

VOL

tRPD

1815_08.eps

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