IMP1232LP/LPS
Application Information
Supply Voltage Monitor
Reset Signal Polarity and Output Stage Structure
TRIP Point Voltage (V)
Tolerance
Select
Tolerance
10%
Min
4.25
4.5
Nominal
4.37
Max
4.49
4.74
RESET is an active LOW signal. It is developed with an open
drain driver. If a pullup resistor is required, typical values are
10kΩ to 50kΩ.
TOL = V
CC
TOL = GND
5%
4.62
1232_t02.eps
RESET is an active High signal developed by a CMOS push-pull
output stage and is the logical opposite to RESET.
Manual Reset Operation
Push-button switch input, PBRST, allows the user to override the
internal trip point detection circuits and issue reset signals. The
pushbutton input is debounced and is normally pulled HIGH
through an internal 40kΩ resistor.
Trip Point Tolerance Selection
With TOL connected to VCC, RESET and RESET become active
whenever VCC falls below 4.5V. RESET and RESET become active
when VCC falls below 4.75V if TOL is connected to ground.
When PBRST is held LOW for the minimum time tPB , both resets
become active and remain active for approximately a minimum
time period of 250ms after PBRST returns HIGH.
After VCC has risen above the trip point set by TOL, RESET and
RESET remain active for a minimum time period of 250ms.
The debounced input is guaranteed to recognize pulses greater
than 20ms. No external pull-up resistor is required, since PBRST
is pulled HIGH by an internal 40kΩ resistor.
On power-down, once VCC falls below the reset threshold RESET
stays LOW and is guaranteed to be 0.4V or less until VCC drops
below 1.2V. The active HIGH reset signal is valid down to a VCC
level of 1.2V also.
The PBRST can be driven from a TTL or CMOS logic line or short-
ed to ground with a mechanical switch.
tR
tPB
PBRST
4.75V
VCCTP
tPDLY
V
IH
4.25V
V
IL
tRST
VCC
tRPU
RESET
RESET
VOH
VOL
VOH
RESET
1232_08.eps
Figure 3. Timing Diagram: Pushbutton Reset
VOL
RESET
1232_05.eps
5V
Figure 1. Timing Diagram: Power Up
IMP1232LP/LPS
8
7
6
5
1
2
3
4
PBRST
TD
VCC
ST
tF
VCC
4.75V
µP
VCCTP
4.25V
TOL
RESET
GND RESET
RESET
1232_06.eps
tRPD
Figure 4. Application Circuit: Pushbutton Reset
RESET
VOH
VOL
RESET
1232_04.eps
Figure 2. Timing Diagram: Power Down
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© 1999 IMP, Inc.
4
IMP [ IMP, INC ]
