ASM1834A/D
Dual 5V and 3.3V
μP
Power Supply
Supervisor with Manual Reset
General Description
The ASM1834 supervisors simultaneously monitor both
3.3V and 5V power sources and generate reset signals
when either supply is out of tolerance. When an out-of-
tolerance condition is detected, the output-reset signal of
the affected supply becomes active and resets the
system microprocessor/microcontroller. On power-up and
after the supply voltage returns to an in-tolerance
condition, the reset signal remains active for pproximately
350ms. This allows the power supply and system
microprocessor to stabilize.
Tolerance levels are independently selectable for both
supplies. Tolerance options are 5% and 10% percent for
the 5V supply and 10% and 20% percent for the 3.3V
supply.
The ASM1834 and ASM1834D have push-pull reset
output stages. The ASM1834A reset outputs are open
drain devices that can both be connected to either 5V or
3.3V supply. The ASM1834 and ASM1834A have active
LOW reset outputs. The ASM1834D has active HIGH
reset outputs.
All devices can generate reset signals through an
internally debounced pushbutton reset input that affects
both reset outputs.
All devices operate over the extended industrial
temperature range. Devices are available in 8-pin DIP,
surface mount 8-pin SO and 8-Pin MicroSO packages.
Die are also available.
Key Features
Monitors 5V and 3.3V supplies simultaneously
5V and 3.3V power-on reset
350ms reset time
Debounced pushbutton reset input
Push-pull CMOS output
ASM1834, ASM1834D
Eliminates external pull-up resistors
Active LOW (ASM1834), HIGH (ASM1834D)
Open Drain Output
ASM1834A
Active LOW
Selectable 5V and 3.3V trip point tolerance
Internal power drawn from highest input voltage, 5V
or 3.3V
Precision temperature-compensated voltage
reference and comparator
Low cost surface mount SO, compact MicroSO and
DIP packages.
Wide operating temperature: -40°C to +85°C
Applications
Microprocessors
PDAs, Hand-held PCs
Embedded Controllers
Telecommunication Systems
Power Supplies
Wireless / Cellular Systems
Networking Hardware
©2010 SCILLC. All rights reserved.
JANUARY 2010 – Rev. 2
Publication Order Number:
ASM1834/D
ASM1834A/D
Typical Operating Circuit
Block Diagram
Rev. 2 | Page 2 of 12 | www.onsemi.com
ASM1834A/D
Pin Configuration
*AS1834D reset outputs are active HIGH (5V RESET and 3.3V RESET) Outputs are open-drain for AS1834A.
Pin Description
Pin #
1
2
3
4
5
6
7
8
Pin Name
5V
IN
5V RESET
5V RESET
5V TOL
GND
PBRST
3.3V TOL
3.3V RESET
3.3V RESET
3.3V
IN
5V power supply input.
5V reset output (Active LOW, ASM1834, ASM1834A. Open drain outputs for ASM1834A).
5V reset output (Active HIGH, AS1834D).
5V input tolerance select: 10% tolerance for 5VTOL= 5V
IN
and 5% tolerance for 5VTOL = GND
Ground.
Debounced manual pushbutton reset input (40kΩ internal pull-up).
3.3V input tolerance select: 20% tolerance for 3.3VTOL = 3.3V
IN
and 10% tolerance for
3.3VTOL=GND.
3.3V reset output (Active LOW, ASM1834, ASM1834A. Open drain outputs for ASM1834A).
3.3V reset output (Active HIGH, AS1834D).
3.3V power supply input.
Function
Detailed Description
Operation Power Monitor
The ASM1834 supervisors simultaneously detect out-of-
tolerance power supply conditions on both 3.3V and 5V
power supplies. If the voltages at 5V
IN
or 3.3V
IN
are
outside the tolerance band, the reset for the falling supply
voltage becomes active. When the monitored supply
returns to an intolerance state, the reset remains active
for approximately 350ms before returning to the inactive
state.
On power-up, the reset signals are kept active for
approximately 350ms after the power supply voltages
have reached the selected tolerance. This allows the
power supply and microprocessor to stabilize before the
reset is removed.
All supply current for the ASM1834 devices is drawn from
the input (5V
IN
or 3.3V
IN
) with the highest voltage level.
The outputs draw current from their input supplies 5V
IN
and 3.3V
IN
.
Rev. 2 | Page 3 of 12 | www.onsemi.com
ASM1834A/D
Reset Signal Polarity and Output Stage Structure
The ASM1834 and the ASM1834A supervisors have
active LOW reset signals. The ASM1834D reset outputs
are active HIGH.
The ASM1834 and the ASM1834D have CMOS push-pull
output stages. The ASM1834A has open drain reset
outputs.
Part #
ASM1834
ASM1834U
ASM1834S
ASM1834A
ASM1834AU
ASM1834AS
ASM1834D
ASM1834DU
ASM1834DS
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
pulled HIGH through an internal 40kΩ resistor.
RESET
Polarity
LOW
LOW
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
Output Stage
Configuration
Push-Pull
Push-Pull
Push-Pull
Open Drain
Open Drain
Open Drain
Push-Pull
Push-Pull
Push-Pull
When at least one of the reset outputs is not asserted, a
push button initiated reset signal can be issued by
holding PBRST LOW for at least 2ms. When PBRST is
held LOW, both resets become active and remain active
for approximately 350ms after PBRST returns HIGH.
(See
Figures 3
and
4.)
Rev. 2 | Page 4 of 12 | www.onsemi.com
ASM1834A/D
Reset Output Signal
Reset output signals are valid as long as either voltage at
5V
IN
or 3.3V
IN
is above 1.2V. In addition, the ASM1834
has push-pull outputs that can remain valid below a 1.2V
input level. To sink current below 1.2V, a resistor should
be connected from the RESET output to ground. This
resistor guarantees a valid reset signal down to 0V. A
100kΩ value is suggested.
The AS1834A open drain reset outputs require pull-up
resistors and must be low enough in value to pull the
output into a HIGH state. Resistor value is not critical in
most applications and a value of 10kΩ is suggested.
(See
Figures 5
and
6.)
The ASM1834A open drain reset outputs can be
connected to the same potential through a single pull-up
resistor. In this configuration a failure on either supply will
generate an active LOW reset. If the inputs are pulled-up
to different voltages, the reset outputs (pin 2 and pin 7)
cannot be connected to form a wired “AND” (see
Figure
7).
Rev. 2 | Page 5 of 12 | www.onsemi.com
