ASM1834/A/D
Alliance Semiconductor
2575 Augustine Drive . Santa Clara, CA 95054 . Tel: 408.855.4900 . Fax: 408.855.4999 . www.alsc.com
Notice: The information in this document is subject to change without notice
rev 1.3
Dual 5V and 3.3V P Power Supply Supervisor with Manual Reset
April 2005
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 approximately 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, -40C to +85C
Applications
Microprocessors
PDAs, Hand-held PCs
Embedded Controllers
Telecommunication Systems
Power Supplies
Wireless / Cellular Systems
Networking Hardware
Typical Operating Circuit
+5V
3.3V
5V
IN
RESET
PBRST
5VTOL
GND
3.3VTOL
3.3V
IN
RESET
GND
P
3.3V
5V
ASM1834
ASM1834/A/D
2 of 10
Notice: The information in this document is subject to change without notice
Dual 5V and 3.3V P Power Supply Supervisor with Manual Reset
rev 1.3
April 2005
Block Diagram
Pin Configuration
Pin Description
Pin #
Pin Name
Function
1
5V
IN
5V power supply input.
2
5V RESET
5V RESET
5V reset output (Active LOW, ASM1834, ASM1834A. Open drain outputs for ASM1834A).
5V reset output (Active HIGH, AS1834D).
3
5V TOL
5V input tolerance select: 10% tolerance for 5VTOL= 5V
IN
and 5% tolerance for 5VTOL = GND
4
GND
Ground.
5
PBRST
Debounced manual pushbutton reset input (40k
internal pull-up).
6
3.3V TOL
3.3V input tolerance select: 20% tolerance for 3.3VTOL = 3.3V
IN
and 10% tolerance for 3.3VTOL=GND.
7
3.3V RESET
3.3V RESET
3.3V reset output (Active LOW, ASM1834, ASM1834A. Open drain outputs for ASM1834A).
3.3V reset output (Active HIGH, AS1834D).
8
3.3V
IN
3.3V power supply input.
1
2
3
4
5
6
7
8
5V
IN
5V RESET *
5V TOL
GND
3.3V
IN
3.3V RESET *
PBRST
3.3V TOL
ASM1834
ASM1834A
ASM1834D
* AS1834D reset outputs are active HIGH (5V RESET and 3.3V RESET)
Outputs are open-drain for AS1834A.
5V Tolerance
Bias
Low TC
3.3V Tolerance
Pushbutton Level
For ASM1834D
350ms Delay
5 V
IN
5 VTOL
PBRST
3.3 V
IN
3.3 VTOL
GND
3.3V RESET
3.3V RESET (ASM1834D)
5V RESET
5V RESET
ASM1834
350ms Delay
Reference
Bias
Sense and Debounce
For ASM1834D
-
+
-
ASM1834A
5V RESET
3.3V RESET
40k
(ASM1834D)
+
1
3
5
8
6
4
7
2
2
7
3 of 10
Notice: The information in this document is subject to change without notice
Dual 5V and 3.3V P Power Supply Supervisor with Manual Reset
ASM1834/A/D
rev 1.3
April 2005
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 5VIN or 3.3VIN are outside
the tolerance band, the reset for the falling supply voltage
becomes active. When the monitored supply returns to an in-
tolerance 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
.
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 #
RESET
Polarity
Output Stage
Configuration
ASM1834
LOW
Push-Pull
ASM1834U
LOW
Push-Pull
ASM1834S
LOW
Push-Pull
ASM1834A
LOW
Open Drain
ASM1834AU
LOW
Open Drain
ASM1834AS
LOW
Open Drain
ASM1834D
HIGH
Push-Pull
ASM1834DU
HIGH
Push-Pull
ASM1834DS
HIGH
Push-Pull
~~
~~
~~
V
OH
V
OL
t
RPU
RESET
RESET
V
INTP
(MIN)
V
INTP
(MAX)
V
INTP
t
R
V
IN
Figure 1: Timing Diagram: Power Up (ASM1834D only)
~ ~
~~
~~
V
OH
V
OL
V
INTP
(MAX)
V
INTP
V
INTP
(MIN)
RESET
RESET
t
F
V
IN
t
RPD
Figure 2: Timing Diagram: Power Down (ASM1834D only)
RESET Slews
with V
CC
4 of 10
Notice: The information in this document is subject to change without notice
Dual 5V and 3.3V P Power Supply Supervisor with Manual Reset
ASM1834/A/D
rev 1.3
April 2005
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 40k
resistor.
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).
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 100k
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 10k
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).
~ ~
~ ~
~ ~
V
OH
V
OL
RESET
RESET
PBRST
t
PB
t
PDLY
V
IH
t
RST
Figure 4: Timing Diagram: Pushbutton Reset
1
2
3
4
5
6
7
8
3.3V
5V
3.3V
IN
3.3V RESET
5VTOL
GND
PBRST
5V
IN
5V RESET
3.3VTOL
ASM1834
Figure 3: Pushbutton Reset
RESET
P
Input
100k
Figure 5: ASM1834 RESET Valid to 0V
1
2
3
4
5
6
7
8
3.3V
5V
3.3V
IN
3.3V RESET
5VTOL
GND
PBRST
5V
IN
5V RESET
3.3VTOL
ASM1834
Figure 6: ASM1834A Open Drain Output Pull-Up Resistor
10k
10k
V
IL
5 of 10
Notice: The information in this document is subject to change without notice
Dual 5V and 3.3V P Power Supply Supervisor with Manual Reset
ASM1834/A/D
rev 1.3
April 2005
Trip Point Tolerance Selection
The 3.3VTOL and 5VTOL inputs allow independent selection of
the reset trip points. If 5VTOL is connected to the 5V supply
input, a 10% tolerance is selected. If 5VTOL is grounded, a 5%
tolerance is selected.
If 3.3VTOL is connected to the 3.3V supply input, a 20%
tolerance is selected. If 3.3VTOL is grounded, a 10% tolerance
is selected. (Refer table below). The 3.3VTOL and 5VTOL
tolerance select inputs should be tied to the ground or to the
respective input supply voltage pin, 3.3V
IN
or 5V
IN
.
Tolerance Select
3.3V Input
5V Input
3.3V
Tolerance
TRIP Point (V)
5V
Tolerance
TRIP Point (V)
MIN
NOM
MAX
MIN
NOM
MAX
5VTOL = 5V
IN
-
-
-
-
10%
4.25
4.38
4.49
5VTOL = GND
-
-
-
-
5%
4.5
4.63
4.75
3.3VTOL = 3.3V
IN
20%
2.47
2.55
2.64
-
-
-
-
3.3VTOL = GND
10%
2.80
2.88
2.97
-
-
-
-
1
2
3
4
5
6
7
8
5V
IN
5VRESET 3.3VRESET
5V or 3.3V
3.3V
IN
5V TOL
GND
3.3V TOL
PBRST
3.3V
ASM1834A
5V
10k
Figure 7: ASM1834A Wired "OR" Connection
PDF 
ZIP