LCMOS, High Speed, 4-Channel 10-Bit ADC

The AD7777 and AD7778 are high speed, multichannel, 10-bit analog-to-digital converters (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 4-channel AD7777 and the 8-channel AD7778, the input channels can be independently sampled or any two channels can be simultaneously sampled. For both the AD7777 and AD7778, the specified input signal range is VBIAS ± VSWING. However, if the RTN pin is biased at, for example, 2 V, the analog input signal range becomes 0 V to 2 V for all input channels (see the Changing the Analog Input Voltage Range section). The bias voltage, VBIAS, is the offset of the midpoint code of the ADC from ground and is supplied either by an onboard reference available to the user (REFOUT) or by an external voltage reference applied to REFIN. The full-scale range (FSR) of the ADC is equal to 2 × VSWING where VSWING is nominally equal to REFIN/2. Additionally, when placed in the half scale conversion mode, the value of REFIN is converted, which allows the channel offsets to be measured.

Control register loading, ADC register reading, channel selection, and the conversion start are under the control of the microprocessor. The twos complement coded ADCs are easily interfaced to a standard 16-bit microprocessor unit bus via their 10-bit data port and standard microprocessor control lines.

The AD7777 / AD7778 are fabricated in linear compatible CMOS (LC2MOS), an advanced, mixed technology process that combines precision bipolar circuits with low power CMOS logic.

The AD7777 is available in a 28-lead, wide-body SOIC package. The AD7778 is available in a 44-lead MQFP.

APPLICATIONS

* Instrumentation

* 4-Channel

* Fast 10-bit ADC

* 5 V supply