AD5758 datasheet(45/72 Pages) AD

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Data Sheet

AD5758

Rev. 0 | Page 45 of 72

ADC Configuration

The ADC is configured using the ADC_CONFIG register via

SEQUENCE_COMMAND (Bits[10:8]), SEQUENCE_DATA

(Bits[7:5]), and ADC_IP_SELECT (Bits[4:0]).

Table 19. ADC Configuration Register

D10 to D8

D7 to D5

D4 to D0

Command

Data

ADC input select

The ADC can be set up to monitor a single node of interest or

configured to sequence through up to eight nodes of interest.

The sequential conversions can be initiated automatically after

every valid SPI frame is received by the device (automatic

sequence mode), or in a more controlled manner via a specific

key code written to the key register (key sequence mode). When

a conversion is complete, the ADC result is available in the status

advanced. If autostatus readback mode is used in conjunction with

either sequence mode, the last completed ADC conversion data is

available on SDO during every SPI frame written to the device.

The sequencer has a maximum channel depth of 8. Each of the

channels in the sequencer must be configured with the select

bits of the required ADC input for that sequencer channel, and

the number of configured channels must equal the depth. If any

active sequencer channel location is not configured correctly, it

stores the previous value loaded to that channel, defaulting

initially to the ADC input option of 0b00000 for all sequencer

channels. If a node from the dc-to-dc die is required to be part

of the ADC sequencer, pe

rform this configuration using the

DCDC_ADC_CONTROL_DIAG bits in the DCDC_CONFIG2

3-wire interface related delays between ADC conversions. If

multiple nodes from the dc-to-dc die are required within the

sequence, key sequencing mode must be used rather than

automatic sequencing mode, because the DCDC_ADC_

CONTROL_DIAG bits must be updated between ADC

conversions to configure the next required dc-to-dc die

node required by the sequence.

The four modes of operation are key sequencing, automatic

sequencing, single immediate conversion, and single key

conversion. The sequencing modes are mutually exclusive. If

enabled, the key sequencing mode disables the automatic

sequencing mode, and vice versa.

Key Sequencing (Command 010)

Writing Command 010 enables key sequencing mode.

Sequencing starts with a write to the key register with Key

Code 0x1 ADC, starting on Channel 0 and continuing to

Channel N − 1, where N is the depth, with every 0x1ADC

command. This mode enables user control of the switching of

channels during sequencing because the switch occurs only for

every specific key code command, rather than for every valid

SPI frame, as in the case of automatic sequencing mode. When

the sequence is completed, it starts again with Channel 0 until

disabled. Command 000 and Command 001 must be used to

configure all the required channels before Command 0b010 is

issued to enable key sequencing mode (see Figure 86). If the

sequencing is disabled and later reenabled, the sequencer is

reset to recommence converting on the first channel in the

sequence.

Automatic Sequencing (Command 011)

Sequencing starts on the next valid SPI frame, starting with

Channel 0 and continuing to Channel N − 1, where N is the depth,

on every valid SPI frame. When the sequence is complete, it starts

again with Channel 0 until disabled. As with the key sequencing

mode, Command 000 and Command 001 must be used to

configure all the required channels before Command 011 is issued

to enable automatic sequencing mode (see Figure 86). If the

sequencing is disabled and later reenabled, the sequencer is

reset to recommence converting on the first channel in the

sequence. When reenabled, the channels do not need to be

reconfigured unless the desired list of nodes changes. Use

automatic sequencing in conjunction with the autostatus

readback mode to ensure that the latest ADC result is available.

Single Immediate Conversion (Command 100)

This mode initiates a single conversion on the node currently

selected in the ADC input select bits of the ADC_CONFIG register.

Selecting this command stops any active automatic sequence,

meaning that it must be reenabled if required. The sequencer

does not need to be reconfigured because the configuration of

sequencer depth and channels is stored.

Single Key Conversion (Command 101)

This mode is used to set up an individual ADC input node to be

converted at some future time, initiated by writing the 0x1ADC

key code to the key register.

Sequencing Mode Setup

A list of the relevant ADC sequencer commands are shown in

Table 20 (these are available in the ADC_CONFIG register; see

Table 42). The default depth (000) is equivalent to one diagnostic

channel up to a binary depth value of 111, which is equivalent

to eight channels.

Table 20. Command Bits

Value

Description

000

Set the sequencer depth (0 to 7)

001

Load sequencer Channel N with the selected ADC input

010

Enable/disable key sequencer

011

Enable/disable automatic sequencer

100

Perform a single conversion on the currently selected

ADC input

101

Set up single key conversion, that is, select the ADC mux

input to be used when triggered with a write to the key

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