Rainbow Electronics LM3813 - Manual

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 av-
eraging function. Current is averaged over 50 msec time
periods in order to provide immunity to current spikes. The
ICs have a pulse-width modulated (PWM) output which indi-
cates 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
current options. The sense range is −1A to +1A or −7A to
+7A. The sampling interval for these parts is 50ms. If faster
sampling 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
n
± 2% accuracy at room temperature (includes accuracy
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
10012201
Top View
LM3812
for High-Side Sensing
10012203
Top View
LM3813
for Low-Side Sensing
June 1999
LM3812/LM3813
Precision
Current
Gauge
IC
with
Ultra
Low
Loss
Sense
Element
and
PWM
Output
© 2004 National Semiconductor Corporation DS100122 www.national.com