Information

1300 Henley Court

Pullman, WA 99163

509.334.6306

www.digilentinc.com

PmodISNS20™ Reference Manual

Revised April 12, 2016

This manual applies to the PmodISNS20 rev. A

DOC#: 502-325

Other product and company names mentioned may be trademarks of their respective owners.

Page 1 of 3

Overview

The Digilent PmodISNS20 is a small current sense module with a digital SPI interface. The board combines

an Allegro ACS722 Hall Effect current sensor with a 12-bit analog-to-digital converter from Texas Instruments. The

PmodISNS20 is quick, accurate, and easy to use for a variety of applications.

1 Functional Description

The PmodISNS20 is designed to send current data over Serial Peripheral Interface to a host board. The

PmodISNS20 sends a 12-bit digital value that represents the amount of current flowing through the terminal block.

It should be mentioned that unlike reading voltage, current is read in series. This digital representation can be used

in software or FPGA logic, displayed, or sent through a serial monitor.

The PmodISNS20.

 High accuracy current sensor

 Measure current with 120Hz/20kHz/80kHz

jumper selections

 ±20A DC or AC input

 Accurate to within ±2%

 12-bit ADC

 Small PCB size for flexible designs 1.3 in ×

0.8 in (3.3 cm × 2.0 cm)

 6-pin Pmod port with SPI interface

 Follows Digilent Pmod Interface

Specification Type 2

 Library and example code available

in resource center

 Current measurement

 Power metering

 Closed loop current control

 Over-current protection

Features include:

Applications:

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300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodISNS20™ Reference Manual Revised April 12, 2016 This manual applies to the PmodISNS20 rev. A Overview The Digilent PmodISNS20 is a small current sense module with a digital SPI interface. The board combines an Allegro ACS722 Hall Effect current sensor with a 12-bit analog-to-digital converter from Texas Instruments. The PmodISNS20 is quick, accurate, and easy to use for a variety of applications.
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PmodISNS20™ Reference Manual 2 Interfacing with the Pmod The PmodISNS20 communicates with the host board via the SPI protocol. The 12 bits of digital data are sent to the system board in 16 clock cycles with the most significant bit first. For the ADC7476, each bit is shifted out on each falling edge of the serial clock line after the chip select line is brought low with the first four bits as leading zeroes and the remaining 12 bits representing the 12 bits of data.
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PmodISNS20™ Reference Manual The scaling value at the beginning of the equation was derived using the provided sensitivity of 66mV/A off of the ACS722 datasheet. Note that the provided sensitivity is based on a reference voltage of 3.3V to the sensor and our design provides a regulated 3.0V for a cleaner signal, so some more correction may be needed if absolute accuracy is needed. Table 2 below shows how to configure the sampling rate frequency.