AMC1304L05DW datasheet(29/46 Pages) TI2

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Gtot

= E

û Modulator

VCM = 2 V

AMC1304

15 V

GND

High Voltage

Potential

R4'

R5'

IIB

rID

LDOIN

AINP

AINN

AGND

R3'

AMC1304L05, AMC1304L25, AMC1304M05, AMC1304M25

www.ti.com

SBAS655F – SEPTEMBER 2014 – REVISED JANUARY 2020

Product Folder Links: AMC1304L05 AMC1304L25 AMC1304M05 AMC1304M25

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Typical Applications (continued)

9.2.2 Isolated Voltage Sensing

The AMC1304 is optimized for usage in current-sensing applications using low-impedance shunts. However, the

device can also be used in isolated voltage-sensing applications if the affect of the (usually higher) impedance of

the resistor used in this case is considered.

Figure 56. Using the AMC1304 for Isolated Voltage Sensing

9.2.2.1

Design Requirements

Figure 56 shows a simplified circuit typically used in high-voltage-sensing applications. The high impedance

resistors (R1 and R2) are used as voltage dividers and dominate the current value definition. The resistance of

the sensing resistor R3 is chosen to meet the input voltage range of the AMC1304. This resistor and the

differential input impedance of the device (the AMC1304x25 is 25 kΩ, the AMC1304x05 is 5 kΩ) also create a

voltage divider that results in an additional gain error. With the assumption of R1, R2, and RIN having a

considerably higher value than R3, the resulting total gain error can be estimated using Equation 4, with EG

being the gain error of the AMC1304.

(4)

This gain error can be easily minimized during the initial system-level gain calibration procedure.

9.2.2.2 Detailed Design Procedure

As indicated in Figure 56, the output of the integrated differential amplifier is internally biased to a common-mode

voltage of 2 V. This voltage results in a bias current IIB through the resistive network R4 and R5 (or R4' and R5')

used for setting the gain of the amplifier. The value range of this current is specified in the Electrical

Characteristics table. This bias current generates additional offset error that depends on the value of the resistor

R3. Because the value of this bias current depends on the actual common-mode amplitude of the input signal (as

illustrated in Figure 57), the initial system offset calibration does not minimize its effect. Therefore, in systems

with high accuracy requirements, TI recommends using a series resistor at the negative input (AINN) of the

AMC1304 with a value equal to the shunt resistor R3 (that is, R3' = R3 in Figure 56) to eliminate the affect of the

bias current.

AMC1304L05DW Datasheet(PDF) 29 Page - Texas Instruments

AMC1304L05DW Datasheet(HTML) 29 Page - Texas Instruments

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