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Notice: The information in this document is subject to change without notice

Dual 5V and 3.3V µP 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

Ω 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

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

Ω 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

Ω 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

RESET

PBRST

Figure 4: Timing Diagram: Pushbutton Reset

1

2

3

4

5

6

7

8

3.3V

5V

3.3V RESET

5VTOL

GND

PBRST

5V RESET

3.3VTOL

ASM1834

Figure 3: Pushbutton Reset

RESET

µP

Input

100kΩ

Figure 5: ASM1834 RESET Valid to 0V

1

2

3

4

5

6

7

8

3.3V

5V

3.3V RESET

5VTOL

GND

PBRST

5V RESET

3.3VTOL

ASM1834

Figure 6: ASM1834A Open Drain Output Pull-Up Resistor

10kΩ

10kΩ