Cirrus Logic AN366 User Manual
An366
Copyright
Cirrus Logic, Inc. 2012
(All Rights Reserved)
Cirrus Logic, Inc.
Application Note
CS5480/84/90 Energy Measurement IC Calibration
1 Introduction
The Cirrus Logic CS5480/84/90 energy measurement IC is designed with industry-leading calibration algorithms
that simplify measurement applications. The CS5480/84/90 calibration is engineered so power meter manufacturers
can use low-cost components to achieve highly accurate power measurement. Calibration methods specified by IC
manufacturers can vary substantially despite the power meter manufacturers’ requirements to comply with tightly
regulated standards. This application note will introduce the procedures available for calibrating the CS5480/84/90
devices, empowering power meter manufacturers to exceed industry standards.
2 Overview
This application note covers system scaling concepts, including hardware scaling, analog front end (AFE) scaling,
and controller (MCU) scaling. The relationship between full-scale measurements and AFE measurements is
discussed, and a corresponding application processor example is presented. The typical hardware configuration
required to perform calibration and compensation is also presented. Then the types of calibrations in the
CS5480/84/90 are detailed. The calibration and compensation procedure is provided in a step-by-step process that
determines the AFE calibration and compensation constants.
Flow diagrams are provided for each calibration and compensation process. The customer demonstration board
(CDB5484U) is used to illustrate the calibration process and provide examples of the serial port reads/writes
transmitted at each calibration step.
Below are the calibration essentials discussed in this document:
- System Scaling
- Types of Calibration and Compensation
- Calibration and Compensation Procedure
- Calibration and Compensation Example with Hardware Configuration
3 System Level Configurations
Upon power-up, the CS5480/84/90 requires an initial register configuration before executing power measurements.
One of the key configurations is adjusting the system scaling for the power meter application. The key scaling
constants are identified through calibration and compensations performed at the power meter manufacturer. After
the configuration and calibration constants are established, the calibration constants are downloaded during a
normal power-on reset. The application will start conversions and report power and input performance over time.
During power conversions and calculations, the analog inputs are sampled at 512 kHz, decimated down to 4kHz
high-rate conversion cycles. The high-rate samples are averaged to produce a 1 second low-rate power
accumulation measurement, which is used to update registers and, when enabled, generate pulses that represent
the power results (N = 4000, MCLK = 4.096 MHz). The CS5480/84/90 performs signal conditioning along the digital
data path, which improves the accuracy of the power meter measurements. Signal conditioning is provided in the
high-rate path (gain, phase, and DC offset) and in the lower rate path (no load current RMS offset, AC offset, active
and reactive power offset).
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