Analog Circuit Design Volume Three

Chapter 13

Microprocessor core supply voltage set by I²C bus without VID lines

Mark Gurries

Abstract

The LTC1699, a precision 2-state resistive divider that uses a simple SMBus interface to allow VID control on non-VID-enabled DC/DC converters, is described.

Keywords

DC/DC converters

LTC1699

SMBus

2-state resistive divider

Introduction

Many modern CPUs run at two different clock speeds, where each speed requires a different core operating voltage to assure optimum performance. These voltages are documented in the manufacturer’s VID (voltage identification) section of the CPU specification. Some new DC/DC converters (the LTC1909, for example) have built-in VID control that supports dual programmable output voltages, but many existing ...