AD7734 datasheet(30/32 Pages) AD

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AD7734

Rev. 0 | Page 30 of 32

I/O Port

The AD7734 P0 pin can be used as a general-purpose digital

I/O pin. The P1 pin (SYNC/P1) can be used as a general-

purpose digital I/O pin or to synchronize the AD7734 with

other devices in the system. When the SYNC bit in the I/O port

process any conversion. If it is put into single conversion mode,

continuous conversion mode, or any calibration mode, the

AD7734 waits until the SYNC pin goes high and then starts

operation. This allows conversion to start from a known point

in time, i.e., the rising edge of the SYNC pin.

The digital P0 and P1 voltage is referenced to the analog

supplies. When configured as inputs, the pins should be tied

high or low.

Calibration

The AD7734 provides zero-scale self-calibration, and zero- and

full-scale system calibration capability that can effectively

reduce the offset error and gain error to the order of the noise.

After each conversion, the ADC conversion result is scaled

using the ADC calibration registers and the relevant channel

calibration registers before being written to the data register.

For unipolar ranges:

Data = ((ADC result – ADC ZS Cal. reg.)

× ADC FS Reg./200000h – Ch. ZS Cal. reg.)

× Ch. FS Cal. reg./200000h

For bipolar ranges:

Data = ((ADC result – ADC ZS Cal. reg.)

× ADC FS Reg./400000h + 800000h – Ch. ZS Cal. reg.)

× Ch. FS Cal. reg./200000h

Where the ADC result is in the range of 0 to FFFFFFh.

Note that the channel zero-scale calibration register has the

format of a sign bit and a 22-bit channel offset value.

It is strongly recommended that the user not change the ADC

full-scale register.

To start any calibration, write the relevant mode bits to the

AD7734 mode register. After the calibration is complete, the

contents of the corresponding calibration registers are updated,

all RDY bits in the ADC status register are set, the SYNC pin

goes low, and the AD7734 reverts to idle mode. The calibration

duration is the same as the conversion time configured on the

selected channel. A longer conversion time gives less noise and

yields a more exact calibration; therefore, use at least the default

conversion time to initiate any calibration.

ADC Zero-Scale Self-Calibration

The ADC zero-scale self-calibration can reduce the offset error

in the chopping disabled mode. If repeated after a temperature

change, it can also reduce the offset drift error in the chopping

disabled mode.

The zero-scale self-calibration is performed on internally

shorted ADC inputs. The negative analog input terminal on the

selected channel is used to set the ADC zero-scale calibration

common mode. Therefore, either the negative terminal of the

selected differential pair or the AINCOM on the single-ended

channel configuration should be driven to a proper common-

mode voltage.

It is strongly recommended that the ADC zero-scale calibration

calibration.

Per Channel System Calibration

If the per channel system calibrations are used, these should be

initiated in the following order: a channel zero-scale system

calibration, followed by a channel full-scale system calibration.

The system calibration is affected by the ADC zero-scale and

full-scale calibration registers. Therefore, if both self-calibration

and system calibration are used in the system, an ADC full-scale

self-calibration should be performed first, followed by a system

calibration cycle.

While executing a system calibration, the fully settled system

zero-scale voltage signal or system full-scale voltage signal must

be connected to the selected channel analog inputs.

The per channel calibration registers can be read, stored, or

modified and written back to the AD7734. Note that when

writing the calibration registers the AD7734 must be in idle

mode. Note that outside the specified calibration range,

calibration is possible but the performance may degrade (see

the System Calibration section in Table 1).

AD7734 Datasheet(PDF) 30 Page - Analog Devices

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