2910I 查看數據表（PDF） - Linear Technology

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2910I

Octal Positive/Negative Voltage Monitor

Linear Technology 

LTC2910

APPLICATIONS INFORMATION

2. Choose RB to complete the design

Once RA is known, RB is determined by:

RB =

Vm

Im

− RA

(2)

If any of the variables Vm, Im, or VUV change, then both

steps must be recalculated.

Positive Voltage Monitor Example

A positive voltage monitor application is shown in Figure

3. The monitored voltage is a 5V ±10% supply. Nominal

current in the resistive divider is 10µA.

1. Find RA to set the UV trip point of the monitor.

RA

=

0.5V

10µA

•

5V

4.5V

≈ 56.2k

2. Determine RB to complete the design.

RB =

5V

10µA

− 56.2k ≈ 499k

Negative Voltage Monitor Example

A negative voltage monitor application is shown in Figure

4. The monitored voltage is a –5V ±10% supply. Nominal

current in the resistive divider is 10µA. For the negative

case, 1V is subtracted from Vm and VUV.

1. Find RA to set the UV trip point of the monitor.

RA

=

0.5V

10µA

•

–5V − 1V

–4.5V − 1V

≈ 54.9k

2.Determine RB to complete the design.

RB =

–5V − 1V

10µA

− 57.6k ≈ 549k

Power-Up/Down

As soon as VCC reaches 1V during power up, theR⎯ S⎯ T⎯ output

asserts low and the RST output weakly pulls to VCC.

The LTC2910 is guaranteed to assert ⎯R⎯S⎯T low and RST

high under conditions of low VCC, down to VCC = 1V. Above

VCC = 2V (2.1V maximum) the Vn inputs take control.

Once all inputs and VCC become valid, an internal timer is

started. After an adjustable delay time, RST pulls low and

⎯R⎯S⎯T weakly pulls high.

Threshold Accuracy

Reset threshold accuracy is important in a supply sensitive

system. Ideally, such a system would reset only if supply

5V ± 10%

5V

VCC

RST

5V

VCC

REF

RST

RB

449k

RA

56.2k

RST

LTC2910

V7

SEL

GND

2910 F02

Figure 3. Positive Supply Monitor

RA

54.9k

RB

549k

RST

LTC2910

V7

SEL

–5V ± 10%

GND

2910 F04

Figure 4. Negative Supply Monitor

2910fb

9

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