MAX1232CSA Maxim Integrated Products, MAX1232CSA Datasheet - Page 4

• Manufacturer Part Number: MAX1232CSA
• Description: IC MPU SUPERVISORY CIRCUIT 8SOIC
• Manufacturer: Maxim Integrated Products
• Type: Simple Reset/Power-On Resetr

Specifications of MAX1232CSA

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active High/Active Low
• Reset Timeout: 250 ms Minimum
• Voltage - Threshold: 4.37V, 4.62V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Case: SOP8
• Dc: 00+
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A voltage detector monitors V
outputs (RST and RST) in their active states whenever
V
or 4.37V, typically). To select the 5% level, connect
TOL to ground. To select the 10% level, connect TOL to
V
until V
mum of 250ms (the reset active time) to allow the
power supply and µP to stabilize.
The RST output both sinks and sources current, while
the RST output, an open-drain MOSFET, sinks current
only and must be pulled high.
The MAX1232’s debounced manual reset input
(PBRST) manually forces the reset outputs into their
active states. The reset outputs go active after PBRST
has been held low for a time t
delay time. The reset outputs remain in their active
states for a minimum of 250ms after PBRST rises above
V
A mechanical pushbutton or an active logic signal can
drive the PBRST input. The debounced input ignores
input pulses less than 1ms and is guaranteed to recog-
nize pulses of 20ms or greater. The PBRST input has
an internal pullup to V
external pullup resistor is not necessary.
Microprocessor Monitor
Figure 1. Pushbutton Reset
4
CC
CC
IH
_______________________________________________________________________________________
(Figure 3).
. The reset outputs will remain in their active states
is below the selected 5% or 10% tolerance (4.62V
CC
has been continuously in-tolerance for a mini-
PB RST
+5V
V
CC
MAX1232
GND
CC
Detailed Description
Pushbutton Reset Input
of about 100µA; therefore, an
TOL
RST
TD
ST
PBD
CC
, the pushbutton reset
I/O
RESET
and holds the reset
MICROPROCESSOR
Power Monitor
The microprocessor drives the ST input with an
input/output (I/O) line. The microprocessor must toggle
the ST input within a set period (as determined by TD)
to verify proper software execution. If a hardware or
software failure keeps ST from toggling within the mini-
mum timeout period—ST is activated only by falling
edges (a high-to-low transition)—the MAX1232 reset
outputs are forced to their active states for 250ms
(Figure 2). This typically initiates the microprocessor’s
power-up routine. If the interruption continues, new
reset pulses are generated each timeout period until ST
is strobed. The timeout period is determined by the TD
input connection. This timeout period is typically 150ms
with TD connected to GND, 600ms with TD floating, or
1200ms with TD connected to V
The software routine that strobes ST is critical. The
code must be in a section of software that executes fre-
quently enough so the time between toggles is less
than the watchdog timeout period. One common tech-
nique controls the microprocessor I/O line from two
sections of the program. The software might set the I/O
line high while operating in the foreground mode, and
set it low while in the background or interrupt mode. If
both modes do not execute correctly, the watchdog
timer issues reset pulses.
Figure 2. Watchdog Timer
+8V
3-TERMINAL
REGULATOR
7805
+5V
0.1µF
V
TD
CC
MAX1232
TOL
CC
GND
Watchdog Timer
RST
.
ST
+5V
10kΩ
RESET
I/O
MICROPROCESSOR