Isolated Sigma-Delta Modulator

AD7401A

Rev. 0

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FEATURES

20 MHz maximum external clock rate

Second-order modulator

16 bits, no missing codes

±2 LSB INL typical at 16 bits

1 μV/°C typical offset drift

On-board digital isolator

On-board reference

±250 mV analog input range

Low power operation: 17 mA typical at 5.5 V

−40°C to +125°C operating range

16-lead SOIC package

Internal clock version: AD7400A

Safety and regulatory approvals

UL recognition

3750 V rms for 1 minute per UL 1577

CSA Component Acceptance Notice #5A

VDE Certificate of Conformity

DIN V VDE V 0884-10 (VDE V 0884-10):2006-12

APPLICATIONS

AC motor controls

Shunt current monitoring

Data acquisition systems

Analog-to-digital and opto-isolator replacements

GENERAL DESCRIPTION

The AD7401A1 is a second-order, sigma-delta (Σ-Δ) modulator

that converts an analog input signal into a high speed, 1-bit data

stream with on-chip digital isolation based on Analog Devices,

Inc., iCoupler® technology. The AD7401A operates from a 5 V

power supply and accepts a differential input signal of ±250 mV

(±320 mV full scale). The analog input is continuously sampled

by the analog modulator, eliminating the need for external

sample-and-hold circuitry. The input information is contained

in the output stream as a density of ones with a data rate up to

20 MHz. The original information can be reconstructed with

an appropriate digital filter. The serial I/O can use a 5 V or a 3 V

The serial interface is digitally isolated. High speed CMOS,

combined with monolithic air core transformer technology,

means the on-chip isolation provides outstanding performance

characteristics, superior to alternatives such as optocoupler

devices. The part contains an on-chip reference. The AD7401A

is offered in a 16-lead SOIC and has an operating temperature

range of −40°C to +125°C.

FUNCTIONAL BLOCK DIAGRAM

Σ-Δ ADC

CONTROL LOGIC

AD7401A

BUF

T/H

REF

WATCHDOG

MDAT

MCLKIN

DECODE

ENCODE

DECODE

ENCODE

UPDATE

WATCHDOG

UPDATE

Figure 1.