AMC1301 Resistive Divider Calculator

Circuit Overview

The resistive voltage divider attenuates a high-voltage source (e.g. mains) down to the ±250 mV full-scale input range of the AMC1300B/AMC1301. The divider consists of R_top = R1 + R2 in series, with R3 as the bottom shunt. An optional R3' on the inverting input compensates for bias-current offset.

    V_source
       |
      [R1]  ── R_top = R1 + R2
       |
      [R2]
       |──────── V_inP ──┐
       |                  │  AMC1300B
      [R3]          [R_ind]  (internal)
       |                  │
       GND ──[R3']── V_inN ──┘

Design Parameters

V_source (peak voltage)

Peak source voltage (e.g. 240 V for mains)

V_{IN_FSR} (AMC full-scale input)

AMC1300B: 250 mV, AMC1301: 250 mV

P_peak (max divider power)

Power budget for the divider resistors

R_ind (differential input impedance)

kΩ

AMC1300B: 22 kΩ (from datasheet)

I_bias (input bias current)

μA

AMC1300B: 30 μA (from datasheet)

AMC Fixed Gain

V/V

AMC1300B: 8.2 V/V

Design I — Simple Divider

Assumes infinite input impedance (good for high-impedance devices like AMC1301).

Gain (V_{IN_FSR} / V_source) —

R_top,min (from power budget) —

R_top (rounded up) —

R1 = R2 —

R3 — Ideal vs. Commercial (E96)

R3 (ideal) —

              R3 (nearest E96)
              —
            

Error Estimates (with E96 R3)

Gain Error —

Offset Error (at input) —

Actual V_in at V_source,max —

Output at V_source = 0 V (offset only)

V_in at 0 V (bias offset) —

V_out at 0 V (after AMC gain) —

Design II — Compensated Divider (with R3')

Accounts for finite input impedance (R_ind) and bias-current offset. Recommended for AMC1300B.

Ideal Values

R3 (ideal, compensated) —

R3' (ideal) —

Nearest Commercial Resistors (E96, 1%)

              R3 (nearest E96)
              —
            

              R3' (nearest E96)
              —
            

Error with Commercial Resistors

Gain Error (with E96 R3) —

Offset Error (at input, with E96 R3 & R3') —

Offset Error (at output) —

Formulas Used

R3 = (Gain × R_top) / (1 − Gain − Gain × 2R_top / R_ind)

R3' = (R_top × R3) / (R_top + R3)

Gain Err = R3 / R_ind × 100%

Offset Err = I_bias × (R3 − R3') at input

Input RC Filter

A capacitor C across R3 forms a low-pass filter to reject high-frequency noise. The cutoff frequency is f_c = 1 / (2π × R3 × C). Enter your desired cutoff frequency to get the recommended C value.

      V_inP
       |
      [R3]──┬──  to AMC input
       |    |
       |   [C]   ← filter cap across R3
       |    |
       GND  GND

Desired cutoff frequency (f_c)

Typical: 50–10k Hz depending on application

Output Summary

V_out,diff at V_source,max —

V_out,CM —

Custom Design — Enter Your Own Resistors

Enter your actual resistor values to see the resulting voltage, gain error, and offset error.

V_source

R3' (0 = not used)

R_ind

I_bias

μA

AMC Differential Gain

V/V

V_CM (output common-mode)

AMC1300B: 1.44 V, AMC1301: 1.44 V

Reference

Based on TI Application Note SBAA350A — Isolated Voltage-Measurement Circuit With ±250-mV Input and Differential Output (Daniel Miller, Alex Smith, June 2020, Rev. September 2021).

E96 resistor series (1% tolerance) used for commercial value selection.

AMC1301 Resistive Divider

Circuit Overview

Design Parameters

Design I — Simple Divider

R3 — Ideal vs. Commercial (E96)

Error Estimates (with E96 R3)

Output at V_source = 0 V (offset only)

Design II — Compensated Divider (with R3')

Ideal Values

Nearest Commercial Resistors (E96, 1%)

Error with Commercial Resistors

Formulas Used

Input RC Filter

Design I — C for R3

Design II — C for R3

Output Summary

Custom Design — Enter Your Own Resistors

Custom Design Results

Divider Output

Errors

Input at V_source = 0 V

AMC Output at V_source,max

AMC Output at V_source = 0 V

Power

Reference

Circuit Overview

Design Parameters

Design I — Simple Divider

R3 — Ideal vs. Commercial (E96)

Error Estimates (with E96 R3)

Output at Vsource = 0 V (offset only)

Design II — Compensated Divider (with R3')

Ideal Values

Nearest Commercial Resistors (E96, 1%)

Error with Commercial Resistors

Formulas Used

Input RC Filter

Design I — C for R3

Design II — C for R3

Output Summary

Custom Design — Enter Your Own Resistors

Custom Design Results

Divider Output

Errors

Input at Vsource = 0 V

AMC Output at Vsource,max

AMC Output at Vsource = 0 V

Power

Reference

Output at V_source = 0 V (offset only)

Input at V_source = 0 V

AMC Output at V_source,max

AMC Output at V_source = 0 V