S1

S1

C

=3pF

INP

C

=3pF

INN

VINN

VINP

VDD1

GND1

GND1

GND1

3pF

R

=28kW

IN

3pF

VINN

VINP

Equivalent

Circuit

R

=

IN

f

C

·

CLK

DIFF

1

(

=10MHz)

f

CLK

C

=3.6pF

IND

GND1

GND1

400W

400W

S2

S2

AGND+0.8V

AGND+0.8V

AMC1200

www.ti.com

SBAS542

– APRIL 2011

THEORY OF OPERATION

INTRODUCTION

The differential analog input of the AMC1200 is a switched-capacitor circuit based on a second-order modulator

stage that digitizes the input signal into a 1-bit output stream. The device compares the differential input signal

voltage difference across VINP and VINN. For the discharge phase, both S1 switches open first and then both

simplified equivalent input circuitry.

Figure 31. Equivalent Input Circuit

The analog input range is tailored to directly accommodate a voltage drop across a shunt resistor used for

current sensing. However, there are two restrictions on the analog input signals, VINP and VINN. If the input

voltage exceeds the range AGND

– 0.5 V to AVDD + 0.5 V, the input current must be limited to 10 mA to prevent

the implemented input protection diodes from damage. In addition, the linearity and the noise performance of the

device are ensured only when the differential analog input voltage remains within

±250 mV.

The isolated digital bit stream is processed by a third-order analog filter on the low-side and presented as a

differential output of the device.

application report SLLA181, ISO72x Digital Isolator Magnetic-Field Immunity (available for download at

www.ti.com).

Copyright

© 2011, Texas Instruments Incorporated

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