Low-Power, SC70/SOT µP Reset Circuits with

Capacitor-Adjustable Reset Timeout Delay

4

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Detailed Description

Reset Output

The reset output is typically connected to the reset input

of a µP. A µP’s reset input starts or restarts the µP in a

known state. The MAX6340/MAX6421–MAX6426 µP

supervisory circuits provide the reset logic to prevent

code-execution errors during power-up, power-down,

and brownout conditions (see Typical Operating

Characteristics).

threshold voltage, RESET remains low for the capacitor-

adjustable reset timeout period.

The MAX6422 active-high RESET output is the inverse

logic of the active-low RESET output. All device outputs

The MAX6340/MAX6423/MAX6425/MAX6426 are open-

drain RESET outputs. Connect an external pullup resis-

tor to any supply from 0 to 5.5V. Select a resistor value

large enough to register a logic low when RESET is

asserted and small enough to register a logic high

while supplying all input current and leakage paths

connected to the RESET line. A 10k

Ω to 100kΩ pullup

is sufficient in most applications.

Selecting a Reset Capacitor

The reset timeout period is adjustable to accommodate

a variety of µP applications. Adjust the reset timeout

SRT and ground. Calculate the reset timeout capacitor

as follows:

Pin Description

PIN

MAX6340

MAX6421

MAX6422

MAX6423

MAX6424

MAX6425

MAX6426

SOT23

SOT143

SC70

SOT23

SOT23

NAME

FUNCTION

1

3

3

5

1

SRT

Set Reset Timeout Input. Connect a capacitor between SRT

and ground to set the timeout period. Determine the period as

2

1

2

3

2, 3

GND

Ground

3

——

4

—

N.C.

Not Internally Connected. Can be connected to GND.

42

1

2

5

Supply Voltage and Reset Threshold Monitor Input

51

4

RESET

the selected reset threshold voltage. RESET remains low for

threshold.

—

44

——

RESET

the selected reset threshold voltage. RESET remains high for

threshold.

MAX6340

MAX6423

MAX6425

MAX6426

SRT

RESET

TIMEOUT

N

GND

RESET

LASER-TRIMMED

RESISTORS

3.3V

10k

Ω

5.0V

5V

SYSTEM

Figure 1. MAX6340/MAX6423/MAX6425/MAX6426 Open-Drain

RESET Output Allows Use with Multiple Supplies