Rainbow Electronics LM3815 - Manual

LM3814/LM3815
Fast Current Gauge IC with Ultra Low Loss Sense
Element and PWM Output
General Description
The LM3814/LM3815 Current Gauges provide easy to use
precision current measurement with virtually zero insertion
loss (typically 0.004
Ω). The LM3814 is used for high-side
sensing and the LM3815 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 6 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 LM3814 and LM3815 are factory-set in two different
current options. The sense range is −1A to +1A or −7A to
+7A. The user specifies a particular part number to match
the current range for a given application. The sampling
interval for these parts is 6ms. If larger sampling interval is
desired for better accuracy, please refer to the data sheets
for the part numbers LM3812 and LM3813.
Key Specifications
n Ultra low insertion loss (typically 0.004 Ω)
n 2V to 5.25V supply range
n
± 3.5% accuracy at room temperature (includes
accuracy of the internal sense element) (LM3814-1.0,
LM3815-1.0)
n Low quiescent current in shutdown mode (typically 2.5
µA)
n 6 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
10101301
Top View
LM3814
for High-Side Sensing
10101303
Top View
LM3815
for Low-Side Sensing
January 1999
LM3814/LM3815
Fast
Current
Gauge
IC
with
Ultra
Low
Loss
Sense
Element
and
PWM
Output
© 2004 National Semiconductor Corporation DS101013 www.national.com