ADR02 datasheet(31/48 Pages) AD

31 / 48 page

Data Sheet

AD5735

Rev. B | Page 31 of 48

ENABLING THE OUTPUT

To correctly write to and set up the part from a power-on

condition, use the following sequence:

1. Perform a hardware or software reset after initial power-on.

2. Configure the dc-to-dc converter supply block. Set the

dc-to-dc switching frequency, the maximum output voltage

allowed, and the dc-to-dc converter phase between channels.

3. Configure the DAC control register on a per-channel basis.

Select the output range, and enable the dc-to-dc converter

block (DC_DC bit). Other control bits can also be config-

ured. Set the INT_ENABLE bit, but do not set the OUTEN

(output enable) bit.

4. Write the required code to the DAC data register. This step

implements a full internal DAC calibration. For reduced

output glitch, allow at least 200 µs before performing Step 5.

5. Write to the DAC control register again to enable the

output (set the OUTEN bit).

Figure 73 provides a flowchart of this sequence.

POWER ON.

STEP 1: PERFORM A SOFTWARE/HARDWARE RESET.

STEP 4:

STEP 2: WRITE TO DC-TO-DC CONTROL REGISTER TO

SET DC-TO-DC CLOCK FREQUENCY, PHASE,

AND MAXIMUM VOLTAGE.

STEP 3: WRITE TO DAC CONTROL REGISTER. SELECT

THE DAC CHANNEL AND OUTPUT RANGE.

SET THE DC_DC BIT AND OTHER CONTROL

BITS AS REQUIRED. SET THE INT_ENABLE BIT

BUT DO NOT SET THE OUTEN BIT.

STEP 5:

WRITE TO ONE OR MORE DAC DATA REGISTERS.

WRITE TO DAC CONTROL REGISTER. RELOAD

ALLOW AT LEAST 200µs BETWEEN STEP 3

AND STEP 5 FOR REDUCED OUTPUT GLITCH.

SEQUENCE AS IN STEP 3. SET THE OUTEN

BIT TO ENABLE THE OUTPUT.

Figure 73. Programming Sequence to Correctly Enable the Output

Reprogramming the Output Range

When changing the range of an output, the same sequence

described in the Enabling the Output section should be used.

It is recommended that the range be set to 0 V (zero scale or

midscale) before the output is disabled. Because the dc-to-dc

switching frequency, maximum output voltage, and phase have

already been selected, there is no need to reprogram these values.

Figure 74 provides a flowchart of this sequence.

STEP 3: WRITE VALUE TO THE DAC DATA REGISTER.

STEP 1: WRITE TO CHANNEL’S DAC DATA

TO 0V (ZERO OR MIDSCALE).

STEP 2: WRITE TO DAC CONTROL REGISTER.

SET THE NEW OUTPUT RANGE. KEEP THE

DC_DC BIT AND THE INT_ENABLE BIT SET.

STEP 4: WRITE TO DAC CONTROL REGISTER.

RELOAD SEQUENCE AS IN STEP 2.

CHANNEL OUTPUT IS ENABLED.

DISABLE THE OUTPUT (OUTEN = 0) AND

SET THE OUTEN BIT TO ENABLE THE

OUTPUT.

Figure 74. Programming Sequence to Change the Output Range

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