November 2006
rev 1.5
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
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).
5V
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
PULSECORE [ PulseCore Semiconductor ]
