ASM1834 Datasheet, PDF (4/10 Pages) Alliance Semiconductor Corporation – Dual 5V and 3.3V uP Power Supply Supervisor with Manual Reset

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).
5V
3.3V
ASM1834
1 _5VIN
3.3V_IN ⁸
2 _{5V RESET 3.3V RESET} ⁷
3 _5VTOL
4 _GND
6
3.3VTOL
5
PBRST
Figure 3: Pushbutton Reset
PBRST
t_PB
t_PDLY
V_IL
V_IH
RESET
RESET
t_RST
V_OH
V_OL
Figure 4: Timing Diagram: Pushbutton Reset
ASM1834/A/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).
RESET
100kΩ
µP
Input
Figure 5: ASM1834 RESET Valid to 0V
5V
3.3V
ASM1834
1 _5VIN
10kΩ
3.3V_IN ⁸
2 _{5V RESET 3.3V RESET} ⁷
3 _5VTOL
4 _GND
6
3.3VTOL
5
PBRST
10kΩ
Figure 6: ASM1834A Open Drain Output Pull-Up Resistor
Dual 5V and 3.3V µP Power Supply Supervisor with Manual Reset
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Notice: The information in this document is subject to change without notice