LM3812/LM3813

Precision Current Gauge IC with Ultra Low Loss Sense

Element and PWM Output

General Description

The LM3812/LM3813 Current Gauges provide easy to use

precision current measurement with virtually zero insertion

loss (typically 0.004

Ω). The LM3812 is used for high-side

sensing and the LM3813 is used for low-side sensing.

A Delta Sigma analog to digital converter is incorporated to

precisely measure the current and to provide a current aver-

aging function. Current is averaged over 50 msec time peri-

ods in order to provide immunity to current spikes. The ICs

have a pulse-width modulated (PWM) output which indicates

the current magnitude and direction. The shutdown pin can

be used to inhibit false triggering during start-up, or to enter

a low quiescent current mode.

The LM3812 and LM3813 are factory-set in two different cur-

rent options. The sense range is −1A to +1A or −7A to +7A.

The sampling interval for these parts is 50ms. If faster sam-

pling is desired, please refer to the data sheets for the part

numbers LM3814 and LM3815.

Key Specifications

n Ultra low insertion loss (typically 0.004

Ω)

n 2V to 5.25V supply range

of the internal sense element) (LM3812-1.0,

LM3813-1.0)

n Low quiescent current in shutdown mode (typically

2.5 µA)

n 50 msec sampling interval

Features

n No external sense element required

n PWM output indicates the current magnitude and

direction

n PWM output can be interfaced with microprocessors

n Precision

∆Σ current-sense technique

n Low temperature sensitivity

n Internal filtering rejects false trips

n Internal Power-On-Reset (POR)

Applications

n Battery charge/discharge gauge

n Motion control diagnostics

n Power supply load monitoring and management

n Resettable smart fuse

Connection Diagrams

DS100122-1

Top View

LM3812

for High-Side Sensing

DS100122-3

Top View

LM3813

for Low-Side Sensing

June 1999

© 1999 National Semiconductor Corporation

DS100122

www.national.com