AD7616BSTZ datasheet(39/51 Pages) AD

39 / 51 page

AD7616

Data Sheet

Rev. 0 | Page 38 of 50

DIAGNOSTICS

DIAGNOSTIC CHANNELS

In addition to the 16 analog inputs, VxA and VxB, the AD7616

can also convert the following diagnostic channels: VCC and the

analog ALDO voltage. The diagnostic channels are selected for

conversion by programming the channel register (see the Channel

tic channels can also be added to the sequencer stack in software

mode, but only provide an accurate reading at throughput rates

<250 kSPS. See Figure 65 for a plot of the deviation from

expected value vs. sampling frequency that can be expected

when using the diagnostic channels.

The expected output for each channel is governed by the

following transfer functions:

(

)

(

)

REF

Code

768

–

(

) (

)

(

)

REF

ALDO

Code

LDO

768

–

Figure 65. Deviation from Expected Value vs. Sampling Frequency

Figure 66. VCC Diagnostic Transfer Function

Figure 67. ALDO Diagnostic Transfer Function

INTERFACE SELF TEST

It is possible to test the integrity of the digital interface by

selecting the communication self test channel in the channel

Selecting the communication self test for conversion forces the

conversion result register to a known fixed output. When

conversion code is read, Code 0xAAAA is output as the

conversion code of ADC A, and Code 0x5555 is output as the

conversion code of ADC B.

CRC

The AD7616 has a cyclic redundancy check (CRC) checksum

mode to improve interface robustness by detecting errors in

data. The CRC feature is available in both software (serial and

parallel) mode and hardware (serial only) mode. The CRC

feature is not available in hardware parallel mode. The CRC

result is contained within the status register. Enabling the CRC

feature enables the status register and vice versa.

In hardware mode, the CRCEN pin controls the CRC feature.

The CRC feature is enabled or disabled when the AD7616 is

released from full reset. The logic level of the CRCEN pin when

the RESET pin is released determines whether the CRC feature is

enabled or disabled. Set the CRCEN pin to 1 to enable the CRC

feature. After the RESET pin is released, the function is fixed

and a full reset via the RESET pin is required to exit the

function and set up an alternative configuration. See the Reset

Functionality section for additional information. After being

enabled, the CRC result is appended to the conversion result and

consists of a 16-bit word, where the first eight bits contain the

channel ID of the last channel pair converted and the last eight

bits are the CRC result. The result is accessed via an extra read

command, as shown in Figure 68.

In software mode, the CRC function is enabled by setting either

the CRCEN bit or the STATUSEN bit in the configuration

750

–750

–500

–250

250

500

600

500

400

300

200

100

SAMPLING FREQUENCY (kSPS)

ALDO ERROR

VCC ERROR

29000

22000

23000

24500

26000

28000

25000

27000

4.50

4.75

5.00

5.50

5.25

VCC (V)

–9000

–8800

–8600

–8400

–8200

–8000

–7800

–7600

–7400

–7200

1.75

1.80

1.85

1.90

1.95

ALDO (V)

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