AN637 Datasheet, PDF (1/8 Pages) Silicon Laboratories – MASTER CONTROLLER RECOMMENDATIONS

AN637
Si890X MASTER CONTROLLER RECOMMENDATIONS
1. Introduction
The Si890x isolated 10-bit monitoring ADCs integrate a 10-bit SAR ADC subsystem, supervisory state machine
and isolated UART (Si8900), I²C/SMbus port (Si8901), or SPI Port (Si8902) into a single 16 SOW package. Based
on Silicon Labs' proprietary CMOS isolation technology, the Si890x series offers isolation ratings of 2.5 or 5.0 kV
and finds use across a wide range of low-frequency analog data acquisition applications including isolated ac line
monitors, sensor interface circuits, power-delivery systems, and solar inverters. Si890x devices operate in slave
mode and must be managed by an external master controller (typically an MCU). This application note provides
useful recommendations for configuring the user's master controller for operation with the Si890x including serial
port resynchronization and recovery from loss of VDD.
2. Si890x Overview
VDDA
VDDB
AIN0
AIN1
AIN2
MUX
PGA
10‐Bit
ADC
VREF
D3[CNFG_0]
Tx
Data _Serial
Rx
Port
Data
Serial I/O
To User’s
Master
VREF
/RST
GNDB
VREF
ADC Subsystem
To All
Blocks
State Machine/
User Registers
Si890x
ISOLATION
GNDB
Figure 1. Si890x Generic Block Diagram
Figure 1 shows a generic block diagram representative of any member of the Si890x family. The Si890x family
requires input and output VDD supplies that are isolated from each other. The input-side supply (VDDA) provides
bias to the ADC subsystem, state machine, serial port, and the input side of the digital isolator. The VDDB supply
powers the isolator output circuits and typically powers the user's master as well. The user's master controller
sends a serial command byte to the Si890x that specifies the ADC operating mode, MUX channel address, and
voltage reference source. Upon receipt of the command byte, the Si890x executes the specified ADC
conversion(s) and makes conversion data available for the master to read at the isolated serial port interface. An
understanding of the integrated CMOS digital isolator operation is necessary to understanding the overall Si890x
operation. For detailed information on Si890x operation, see the Si890x data sheet available for download at
www.silabs.com/isolation.
Rev. 0.1 10/11
Copyright © 2011 by Silicon Laboratories
AN637