AN329 Datasheet, PDF (1/4 Pages) Silicon Laboratories – EXTENDING THE FULL-SCALE RANGE

AN329
EXTENDING THE FULL-SCALE RANGE OF THE Si85XX
1. Introduction
This application note describes a technique for extending the full-scale range of the Silicon Labs Si85xx series of
ac current sensors. The Si85xx family of unidirectional ac current sensors is available in full-scale ranges of 5, 10,
and 20 A, and offers size, performance, and cost advantages over older current sensing technologies, such as
current transformers, Hall effect devices, and other approaches. For more information, see the Si85xx Data Sheet.
2. Si85xx Operation
The Si85xx family of current sensors, shown in Figure 1, use inductive current sensing and onboard signal
conditioning electronics to generate a 2 V full-scale output signal proportional to the ac current flowing from the IIN
to the IOUT terminals, to a maximum of 20 A. Current flowing through the metal package slug induces a signal in
the pickup coil onboard the Si85xx die. This signal is applied to the input of an integrator that reconstructs the ac
current flowing from IIN to IOUT. Onboard circuitry provides cycle-by-cycle integrator reset and temperature and
offset voltage compensation to achieve measurement accuracy to within ±5%.
Current
Gate Control
Timing
RESET LOGIC
Si85xx
SEMICONDUCTOR DIE
INTEGRATOR
SIGNAL CONDITIONING
Output
TEMP
SENSOR
ADC
AUTO CALIBRATION
LOGIC
Figure 1. Si85xx Unidirectional AC Sensor Block Diagram
Rev. 0.3 10/07
Copyright © 2007 by Silicon Laboratories
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