SBAA553 July 2022 AMC3301 , AMC3301-Q1 , AMC3302 , AMC3330 , AMC3330-Q1 , AMC3336 , AMC3336-Q1
Design Goals
Voltage Source | AMC3330 Input Voltage | AMC3330 Output Voltage | ||||
---|---|---|---|---|---|---|
V_{A} | V_{B} | Resulting V_{LL} | V_{IN DIFF, MIN} | V_{IN DIFF, MAX} | V_{OUT DIFF, MIN} | V_{OUT DIFF, MAX} |
277 V_{AC} ∠0° |
277 V_{AC} ∠120° |
±480 V | –1 V | +1 V | –2 V | +2 V |
Design Description
This circuit performs a split-tap line-to-line isolated voltage-sensing measurement utilizing the AMC3330 isolated amplifier and a voltage-divider circuit. The line-to-line measurement is taken between two 277 V_{AC} sources that are 120° out of phase. The voltage-divider circuit reduces the line-to-line voltage from ±480 V to ±1 V which matches the input voltage range of the AMC3330. The AMC3330 can measure differential signals of ±1 V with a fixed gain of 2 V/V. The AMC3330 has a differential input impedance of 1.2 GΩ and a low input bias current of 2.5 nA, which support low gain-error and low offset-error signal-sensing in high-voltage applications.
By using the split-tap configuration on a balanced three-phase AC voltage system, two line-to-line voltage measurements are sufficient to measure all three line-to-neutral voltages through derivation.
Design Notes
Design Steps
DC Transfer Characteristics
The following graph shows the simulated differential output of the AMC3330 for a ±800-V input. The output voltage is about 2 V for an input voltage of 480 V, as calculated on the previous page.
AC Transfer Characteristics
The simulated gain is –47.62 dB which closely matches the expected gain for the voltage divider and AMC3330.
Simulation Results
The following simulation shows the input and output signals of the AMC3330.
Design References
Design Featured Isolated Op Amp
AMC3330 | |
---|---|
Input Voltage range | ±1 V |
Nominal Gain | 2 |
Input Resistance | 0.8 GΩ (typ) |
Small Signal Bandwidth | 375 kHz |
Input Offset Voltage and Drift | ±0.3 mV (max), ±4 µV/°C (max) |
Gain Error and Drift | ±0.2% (max), ±45 ppm/°C (max) |
Nonlinearity and Drift | 0.02% (max), ±0.4 ppm/°C (typ) |
Isolation Transient Overvoltage | 6 kV_{PEAK} |
Working Voltage | 1.2 kV_{RMS} |
Common-mode transient immunity, CMTI | 85 kV/µs (min) |
AMC3330 |
Design Alternate Isolated Op Amp
ISO224B | |
---|---|
VDD1 | 4.5 V–18 V |
VDD2 | 4.5 V–5.5 V |
Input Voltage range | ±12 V |
Nominal Gain | ⅓ |
V_{OUT} | Differential ±4 V on output common-mode of VDD2 / 2 |
Input Resistance | 1.25 MΩ (typ) |
Small Signal Bandwidth | 275 kHz |
Input Offset Voltage and Drift | ±5 mV (max), ±15 µV/°C (max) |
Gain Error and Drift | ±0.3% (max), ±35 ppm/°C (max) |
Nonlinearity and Drift | 0.01% (max), ±0.1 ppm/°C (typ) |
Isolation Transient Overvoltage | 7 kV_{PEAK} |
Working Voltage | 1.5 kV_{RMS} |
Common-mode transient immunity, CMTI | 55 kV/µs (min) |
ISO224 |