8-Channel, high-accuracy Li-Ion battery monitoring IC

June 12, 2017 // By Graham Prophet
Analog Devices recently posted details of the AD7284, an IC that contains all the functions required for the general-purpose monitoring of stacked Li-Ion batteries in hybrid electric vehicles and battery backup applications.

The AD7284 has multiplexed cell voltage and auxiliary, analogue-to-digital converter (ADC) measurement channels supporting battery management of four to eight cells. The device provides a maximum total unadjusted error, TUE, (cell voltage accuracy) of ±3 mV that includes all the internal errors from input to output. The primary ADC resolution is 14 bits.

 

The AD7284 also includes an integrated secondary measurement path that validates the data on the primary ADC. Other diagnostic features include the detection of open inputs, communication, and power supply related faults.

 

The AD7284 generates cell balancing interface outputs to drive external FETs to control discharging of individual cells, in order to maintain even state-of-charge across a battery stack. There are two on-chip 2.5 V voltage references: one reference for the primary measurement path, and one for the secondary measurement path.

 

The AD7284 operates from a single supply, ranging from 10V to 40V. The device provides eight differential analogue input channels (shown as a multiplexed single pin on the diagram) to accommodate large common-mode signals across the full VDD range. Each channel allows an input signal range, VPINx − VPIN(x − 1) and VSINx – VSIN(x − 1), of 0V to 5 , where x = 0 to 8. The input pins assume a series stack of eight cells. The AD7284 includes four auxiliary ADC input channels that can be used for temperature measurement or system diagnostics.

 

The AD7284 has a differential daisy-chain interface that allows multiple devices to be stacked without the need for individual device isolation. By design, this interface allows both device to device communication within the same module and communication between devices on different modules. Very low measurement latency is enabled across 96 cells; stack voltage measurement achieves ±16 mV typical battery stack voltage (TUE) accuracy. Four auxiliary analogue input channels, also to a 14-bit ADC, accept thermistor inputs and external diagnostics.

 

Analog Devices; www.analog.com/en/products/analog-to-digital-converters/ad7284.html#product-overview