April 2005
rev 1.3
ASM1834/A/D
Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
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.
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.
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
Typical Operating Circuit
3.3V
+5V
ASM1834
5V
IN
3.3V
IN
RESET
PBRST
5VTOL GND 3.3VTOL
3.3V
5V
µP
RESET
GND
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
April 2005
rev 1.3
ASM1834/A/D
Block Diagram
1
5 V
IN
ASM1834
5V Tolerance
Bias
Low TC
Reference
40kΩ
+
For ASM1834D
ASM1834A
2
5V RESET
5 VTOL
3
350ms Delay
2 5V RESET
5V RESET
(ASM1834D)
7
-
Pushbutton Level
Sense and Debounce
3.3V RESET
PBRST
3.3 V
IN
5
8
3.3 VTOL 6
4
3.3V Tolerance
Bias
+
For ASM1834D
350ms Delay
7
3.3V RESET
3.3V RESET (ASM1834D)
GND
-
Pin Configuration
5V
IN
5V RESET *
5V TOL
GND
1
2
3
4
8
3.3V
IN
3.3V RESET *
3.3V TOL
PBRST
ASM1834
ASM1834A
ASM1834D
7
6
5
* 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.
Function
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.
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Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
Notice: The information in this document is subject to change without notice
April 2005
rev 1.3
ASM1834/A/D
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.
RESET
V
OH
RESET
V
IN
V
INTP
(MAX)
V
INTP
V
INTP
(MIN)
t
F
t
RPD
RESET Slews
with V
CC
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
.
Figure 2: Timing Diagram: Power Down (ASM1834D only)
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.
t
R
V
INTP
(MAX)
V
INTP
(MIN)
V
INTP
~
~
~
RESET
Polarity
LOW
LOW
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
V
OL
~~
Part #
ASM1834
Output Stage
Configuration
Push-Pull
Push-Pull
Push-Pull
Open Drain
Open Drain
Open Drain
Push-Pull
Push-Pull
Push-Pull
~
~
V
IN
t
RPU
RESET
V
OH
ASM1834U
ASM1834S
ASM1834A
V
OL
RESET
Figure 1: Timing Diagram: Power Up (ASM1834D only)
~
~
~~
ASM1834AU
ASM1834AS
ASM1834D
ASM1834DU
ASM1834DS
Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
Notice: The information in this document is subject to change without notice
3 of 10
April 2005
rev 1.3
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.
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
ASM1834/A/D
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
5V
3.3V
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).
ASM1834
1
5V
IN
3.3V
IN
8
2
5V RESET 3.3V RESET
7
3
4
5VTOL
GND
3.3VTOL
PBRST
6
5
Figure 3: Pushbutton Reset
RESET
100kΩ
µP
Input
PBRST
t
PDLY
V
IL
t
PB
V
IH
Figure 5: ASM1834 RESET Valid to 0V
5V
3.3V
~
~
t
RST
ASM1834
V
OH
V
OL
RESET
RESET
10kΩ
1
5V
IN
3.3V
IN
8
10kΩ
Figure 4: Timing Diagram: Pushbutton Reset
Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
Notice: The information in this document is subject to change without notice
~~
~~
2
5V RESET 3.3V RESET
7
3
4
5VTOL
GND
3.3VTOL
PBRST
6
5
Figure 6: ASM1834A Open Drain Output Pull-Up Resistor
4 of 10
April 2005
rev 1.3
ASM1834/A/D
5V
3.3V
5V or 3.3V
ASM1834A
1
2
3
5V TOL
4
GND
PBRST
3.3V TOL
5
5V
IN
3.3V
IN
8
7
6
10kΩ
5VRESET 3.3VRESET
Figure 7: ASM1834A Wired “OR” Connection
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
.
3.3V Input
Tolerance Select
3.3V
Tolerance
-
-
20%
10%
TRIP Point (V)
MIN
-
-
2.47
2.80
NOM
-
-
2.55
2.88
MAX
-
-
2.64
2.97
5V
Tolerance
10%
5%
-
-
5V Input
TRIP Point (V)
MIN
4.25
4.5
-
-
NOM
4.38
4.63
-
-
MAX
4.49
4.75
-
-
5VTOL = 5V
IN
5VTOL = GND
3.3VTOL = 3.3V
IN
3.3VTOL = GND
Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
Notice: The information in this document is subject to change without notice
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