AD7778

a FEATURES AD7776: Single Channel AD7777: 4-Channel AD7778: 8-Channel Fast 10-Bit ADC: 2.5 ␮s Worst Case +5 V Only Half-Scale Conversion Option Fast Interface Port Power-Down Mode APPLICATIONS HDD Servos Instrumentation GENERAL DESCRIPTION LC2MOS, High Speed 1-, 4- & 8-Channel 10-Bit ADCs AD7776/AD7777/AD7778* FUNCTIONAL BLOCK DIAGRAMS CLKIN CONTROL REGISTER 10 AIN 1 MUX T/H 10-BIT ADC ADCREG1 10 CREFIN VBIAS REFIN RTN VSWING CONTROL LOGIC AGND REF REFOUT REFIN DB0–DB9 VCC AD7776 AGND VCC The AD7776, AD7777 and AD7778 are a family of high speed, multichannel, 10-bit ADCs primarily intended for use in R/W head positioning servos found in high density hard disk drives. They have unique input signal conditioning features that make them ideal for use in such single supply applications. By setting a bit in a control register within both the four-channel version, AD7777, and the eight-channel version, AD7778, the input channels can either be independently sampled or any two channels of choice can be simultaneously sampled. For all versions the specified input signal range is of the form VBIAS ± VSWING. However, if the RTN pin is biased at, say, 2 V the analog input signal range becomes 0 V to +2 V for all input channels. This is covered in more detail under the section Changing the Analog Input Voltage Range. The voltage VBIAS is the offset of the ADC’s midpoint code from ground and is supplied either by an onboard reference available to the user (REFOUT) or by an external volta...