AS1907, AS1908 , AS1909

Low-Vo ltage Microprocessor Reset Circuits

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1 General Description

The AS1907/AS1908/AS1909 microprocessor supervi-

sory circuits are ideal for monitoring the supply voltage

of digital systems and microprocessors.

The devices are designed to initiate a reset if the supply

voltage goes below a predefined threshold. The duration

of the reset is either 1.5, 30, or 150ms (typ.) after the

supply voltage has risen above the pre-set threshold

(see Ordering Information on page 9).

The devices are available as the standard products

listed in Table 1.

The reset thresholds are factory-set between 1.6 and

2.5V in steps of approximately 100mV (see Table 5 on

page 7).

The devices exhibit excellent reliability, and can reduce

system costs by eliminating the need for external com-

ponents. The extremely low current consumption makes

the devices ideal for use in portable applications.

The integrated reset comparator was specifically

The devices are available in a 3-pin SOT23 package.

Figure 1. Application Diagrams

2 Key Features

!

3 Output Types: Push/Pull RESET, Push Pull

RESETN, and Open Drain RESETN

!

Reset Threshold Range: 1.6 to 2.5V (~100mV incre-

ments)

!

RESET/RESETN:

!

Reset Pulse Widths: 1, 20, and 100ms

!

Supply Voltage Range: +0.7 to +3.6V

!

Supply Current Range: 2.6 to 7.0µA

!

Power Supply Transient Immunity

!

Requires No External Components

!

Operating Temperature Range: -40 to +125ºC

!

3-pin SOT23 Package

3 Applications

The devices are ideal for use in cordless and mobile

phones, MP3 players, CD and DVD players, PDAs,

handheld computers, digital cameras, hard drives, and

any other application where power supply supervisory

control is required.

Table 1. Standard Products

Model

Output Type

Reset Type

AS1907

Push/Pull

Active-Low

AS1908

Push/Pull

Active-High

AS1909

Open-Drain

Active-Low

2

RESET

AS1908

Micro-

processor

GND

1

3

3

RESET I/O

RESETN

2

AS1907

GND

1

3

GND

1

Micro-

processor

3

RESET I/O

GND

1

2

RESETN

AS1909

Micro-

processor

GND

1

3

3

RESET I/O

GND

1