ATM90E32 — 3-Phase Polyphase Energy Metering IC

Overview

The ATM90E32 (ATM90E32AS) is a high-performance 3-phase polyphase Analog Front End (AFE) energy metering IC manufactured by Microchip Technology (formerly Atmel). Built for utility-grade electricity meters, smart solar inverters, and whole-house panel energy monitors, it integrates six 16-bit ADCs to simultaneously measure 3-phase AC voltage and 3-phase AC current.

Achieving Class 0.2 accuracy across a 6000:1 dynamic range, the ATM90E32 computes active power (W), reactive power (VAR), apparent power (VA), active energy (kWh), RMS voltage ( $V_{RMS}$ ), RMS current ( $I_{RMS}$ ), grid frequency (Hz), power factor (PF), phase angles, and harmonic distortion per phase over a 4-wire SPI bus. It is widely used in ESPHome multi-channel energy monitors and IoTaWatt hardware.

Quick reference


Operating voltage (`VDD`)	3.0 V to 3.6 V DC (3.3 V nominal)
Phases supported	3-Phase 4-Wire (Wye), 3-Phase 3-Wire (Delta), or 3 Single-Phase Circuits
ADC architecture	6 independent 16-bit Sigma-Delta ADCs (3 Voltage + 3 Current)
Metering accuracy	Class 0.2 ( $\pm 0.2\%$ )
Dynamic range	6000 : 1
Interface	4-Wire SPI (up to 2 MHz)
Current inputs	Supports Current Transformers (CT coils) or Rogowski coils
Voltage inputs	Supports AC-AC Voltage Transformers (VT) or resistor dividers

Pinout (48-Pin TQFP Package & SPI Header)

SPI Header & Analog Sensing Pins:

Pin	Name	Type	Description
1	`VDD`	Power	Digital core supply (+3.3 V DC)
2	`GND`	Power	Ground reference (0 V)
3	`CS` / `SS`	Digital Input	Active-Low SPI Chip Select
4	`SCLK`	Digital Input	SPI Serial Clock
5	`SDI` / `MOSI`	Digital Input	SPI Data Input
6	`SDO` / `MISO`	Digital Output	SPI Data Output
7	`IRQ0` / `WARN`	Digital Output	Active-Low interrupt output (voltage sag / over-current)
8–10	`VP`, `VN`, `VP2`	Analog Input	Phase A, B, C Voltage sense inputs ( $V_{peak} \le 800\text{ mV}$ )
11–16	`I1P`/`I1N`, `I2P`/`I2N`, `I3P`/`I3N`	Analog Input	Phase A, B, C Current transformer differential inputs ( $V_{peak} \le 800\text{ mV}$ )

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Supply Voltage	$V_{DD}$	3.0	3.3	3.6	V	DC
Active Supply Current	$I_{DD}$	—	13.0	18.0	mA	All 6 ADCs active
Active Energy Accuracy	$E_{act}$	-0.2%	$\pm 0.1\%$	+0.2%	—	Dynamic range 6000:1
Reactive Energy Accuracy	$E_{react}$	-0.2%	$\pm 0.1\%$	+0.2%	—	Dynamic range 6000:1
Voltage Analog Input	$V_{IN\_V}$	-800	—	+800	mV Peak	Differential peak voltage
Current Analog Input	$V_{IN\_I}$	-800	—	+800	mV Peak	Differential peak voltage
SPI Clock Frequency	$f_{SPI}$	0	1.0	2.0	MHz	SPI Mode 3 ( $CPOL=1, CPHA=1$ )

Polyphase Register Map

Registers are 16-bit words accessed over SPI:

Address	Register Name	Unit	Description
`0xD1`	`UrmsA`	$0.01\text{ V}$	Phase A RMS Voltage
`0xD2`	`UrmsB`	$0.01\text{ V}$	Phase B RMS Voltage
`0xD3`	`UrmsC`	$0.01\text{ V}$	Phase C RMS Voltage
`0xDD`	`IrmsA`	$0.001\text{ A}$	Phase A RMS Current
`0xDE`	`IrmsB`	$0.001\text{ A}$	Phase B RMS Current
`0xDF`	`IrmsC`	$0.001\text{ A}$	Phase C RMS Current
`0xE1`	`PmeanA`	$0.001\text{ W}$	Phase A Active Power
`0xF1`	`PFmeanA`	$0.001$	Phase A Power Factor

Wiring

ATM90E32 Pin	ESP32 GPIO	Arduino (3.3V)	Notes
`VDD`	3.3V	3.3V	Power rail
`GND`	GND	GND	System ground
`SCLK`	GPIO 18	Digital D13	SPI Clock
`SDO` (MISO)	GPIO 19	Digital D12	SPI MISO
`SDI` (MOSI)	GPIO 23	Digital D11	SPI MOSI
`CS`	GPIO 5	Digital D10	SPI Chip Select

Example (ESPHome Configuration snippet)

yaml

sensor:
  - platform: atm90e32
    cs_pin: GPIO5
    phase_a:
      voltage:
        name: "Phase A Voltage"
      current:
        name: "Phase A Current"
      power:
        name: "Phase A Power"
      gain_voltage: 36704
      gain_current: 38532
    phase_b:
      voltage:
        name: "Phase B Voltage"
      current:
        name: "Phase B Current"
      power:
        name: "Phase B Power"
      gain_voltage: 36704
      gain_current: 38532
    phase_c:
      voltage:
        name: "Phase C Voltage"
      current:
        name: "Phase C Current"
      power:
        name: "Phase C Power"
      gain_voltage: 36704
      gain_current: 38532
    frequency:
      name: "Grid Frequency"

Common mistakes

SPI Mode Misconfiguration: The ATM90E32 requires SPI Mode 3 ( $CPOL=1, CPHA=1$ ). Setting Mode 0 results in corrupted SPI register reads (0xFFFF or zero values).
Exceeding $\pm 800\text{ mV}$ peak analog inputs: The differential current/voltage inputs connect directly to internal 16-bit Sigma-Delta ADCs. Signals exceeding $800\text{ mV}$ peak saturate the ADCs and distort calculations. Ensure burden resistors on CT coils step down current signals below $500\text{ mV}$ RMS.

Notes

ATM90E32 vs ATM90E26: ATM90E26 is single-phase ( $1\times \text{Voltage}, 2\times \text{Current}$ ); ATM90E32 is 3-phase polyphase ( $3\times \text{Voltage}, 3\times \text{Current}$ ).

Interface	SPI
Supply	3–3.6 V
Package	48-pin TQFP (7 x 7 mm) / Breakout Module