IMP18 1 5
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 V
CC
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 V
CC
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 V
CC
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
V
CC
approaching 0V. During both power up and down, this con-
figuration will draw current when RESET is in the high state. A
value of 100kΩ should be adequate to maintain a valid condition.
t
R
V
CCTP
(MAX)
V
CCTP
(MIN)
V
CCTP
IMP1815
Microprocessor
RESET
100k
RESET
1815_06.eps
1815_07.eps
V
CC
t
RPU
V
OH
RESET
Figure 1. RESET Valid to 0V V
CC
Figure 2. Timing Diagram: Power-Up
t
F
V
CC
V
CCTP
(MAX)
V
CCTP
V
CCTP
(MIN)
t
RPD
RESET
V
OL
1815_08.eps
Figure 3. Timing Diagram: Power-Down
4
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©
1999 IMP, Inc.
A1PROS [ A1 PROS CO., LTD. ]
