ADM709 Analog Devices, ADM709 Datasheet - Page 3

• Manufacturer Part Number: ADM709
• Description: Power Supply Monitor with Reset
• Manufacturer: Analog Devices

Specifications of ADM709

• # Of Monitored Voltages: 1
• Backup-battery Switch: No
• Manual Reset Capability: No
• Package: DIP,SOIC
• Reset Threshold Summary: 5 Options--2.63 to 4.65V
• Reset Output-stage: Active-Low/Push-Pull
• Min Reset Timeout (ms): 140
• Watchdog Timer: No

REV. 0
CIRCUIT INFORMATION
RESET Output
RESET is an active low output which provides a reset signal to
the microprocessor whenever the V
the reset threshold. An internal timer holds RESET low for
140 ms after the voltage on V
is intended as a power-on reset signal for the processor. It allows
time for the power supply and microprocessor to stabilize after
power up. Similarly a power supply brownout will initiate a pro-
cessor reset. On power-down, the RESET output remains low
with V
held in a stable shutdown condition as the power supply drops.
CC
RESET
RESET
V
V
as low as 1 V. This ensures that the microprocessor is
CC
V
CC
Figure 3. Power Off/On RESET Timing
CC
Figure 1. Functional Block Diagram
Figure 2. Typical Operating Circuit
Figure 4. RESET Output vs. V
V
TH
VRT
ADM709
GND
V
CC
RESET
ADM709
VRT
GND
CC
400ms/DIV
rises above the threshold. This
GENERATOR
CC
t
RS
RESET
supply voltage is below
RESET
V
GND
µP
CC
CC
RESET
–3–
RESET at Voltages < 1 V
The ADM709 RESET output is guaranteed to operate with
supply voltages as low as 1 V. If it is desired that the RESET
output remains low below 1 V, then a pull-down resistor should
be connected between the RESET output and GND. A resistor
of 100 k is suitable. This is illustrated in Figure 5.
Glitch Immunity
The ADM709 is immune to short transients which may occur
on the V
generated as a result of minor glitches on the power supply.
Additional glitch immunity may be obtained by connecting a
capacitor (0.1 F or greater) as close as possible to the V
on the device.
Microprocessors with Bidirectional I-O
Some microprocessors or microcontrollers such as the
MC68HC11 have bidirectional reset lines. In order to avoid
signal contention, a resistor of 4.7 k should be connected
between the ADM709 RESET output and the microcontroller
RESET line. This arrangement is shown in Figure 6.
Figure 6. Interfacing to Microprocessors with
Bidirectional RESET
CC
line. This is important so that spurious resets are not
Figure 5. RESET Valid @ V
ADM709
GND
+5V
V
CC
RESET
ADM709
GND
RESET
R1
RESET
CC
GND
BUFFERED
RESET
µP
< 1 V
ADM709
CC
pin