CS5571

DS768A5

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6/25/07

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2. OVERVIEW

The CS5571 is a 16-bit analog-to-digital converter capable of 100 kSps conversion rate. The analog input

tiple input channels at a high rate with no loss in throughput. The ADC uses a low-latency digital filter ar-

chitecture. The filter is designed for fast settling and settles to full accuracy in one conversion.

The converter is a serial output device. The serial port can be configured to function as either a master or

a slave.

The CS5571 provides self-calibration circuitry to achieve low offset and gain errors.

The converter can operate from an analog supply of 5V or from ±2.5V. The digital interface supports stan-

dard logic operating from 1.8, 2.5, or 3.3 V.

The CS5571 may convert at rates up to 100 kSps when operating from a 16 MHz input clock.

3. THEORY OF OPERATION

The CS5571 converter provides high-performance measurement of DC or AC signals. The converter in-

cludes on-chip calibration circuitry to minimize offset and gain errors. The converter can be used to per-

form single conversions or continuous conversions upon command. Each conversion is independent of

previous conversions and settles to full specified accuracy, even with a full-scale input voltage step. This

is due to the converter architecture which uses a combination of a high-speed delta-sigma modulator and

a low-latency filter architecture.

Once power is established to the converter, a reset must be performed. A reset initializes the internal con-

verter logic and sets the offset register to zero and the gain register to a decimal value of 1.0. If the CAL

pin is low when RST returns high, no calibration will be performed. If CAL is high when RST transitions

from low to high, the converter’s offset & gain slope will be calibrated.

If CONV is held low then the converter will convert continuously with RDY falling every 160 MCLKs. This

is equivalent to 100 kSps if MCLK = 16.0 MHz. If CONV is tied to RDY, a conversion will occur every 162

MCLKs. If CONV is operated asynchronously to MCLK, it may take up to 164 MCLKs from CONV falling

to RDY falling.

Multiple converters can operate synchronously if they are driven by the same MCLK source and CONV

to each converter falls on the same MCLK falling edge. Alternately, CONV can be held low and all devices

are reset with RST rising on the same falling edge of MCLK.

The output coding of the conversion word is a function of the BP/UP pin.

3.1 Reset and Calibration

After the power supplies and the voltage reference are stable, the converter must be reset. The reset func-

tion initializes the internal logic in the converter, but does not initiate calibration. After reset has been per-

formed, the converter can be used uncalibrated, or calibration can be performed. Calibration minimizes

offset and gain errors inside the converter. If the device is used without calibration, conversions will in-

clude the offset and gain errors of the uncalibrated converter, but the converter will maintain its differential

and integral linearity. Calibration of offset and gain can be performed upon command.

Calibration can be initiated in either of two ways. If CAL is high when RST transitions from low to high a

calibration cycle will be performed immediately after a reset is performed. When calibration is performed,

the offset and full-scale points of the converter are calibrated. A calibration cycle takes 327,680 MCLK