Datasheet

AD5757 Data Sheet
Rev. D | Page 26 of 44
PROGRAMMING SEQUENCE TO WRITE/ENABLE
THE OUTPUT CORRECTLY
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. The dc-to-dc converter supply block must be configured.
Set the dc-to-dc switching frequency, maximum output
voltage allowed, and the phase that the four dc-to-dc
channels clock at.
3. Configure the DAC control register on a per channel basis.
The output range is selected, and the dc-to-dc converter
block is enabled (DC_DC bit). Other control bits can be
configured at this point. Set the INT_ENABLE bit;
however, the output enable bit (OUTEN) should not be set.
4. Write the required code to the DAC data register. This
implements a full DAC calibration internally. Allow at least
200 µs before Step 5 for reduced output glitch.
5. Write to the DAC control register again to enable the
output (set the OUTEN bit).
A flowchart of this sequence is shown in Figure 51.
POWER ON.
STEP 1: PERFORM A SOFTWARE/HARDWARE RESET.
STEP 4: WRITE TO EACH/ALL DAC DATA REGISTERS.
ALLOW AT LEAST 200µs BETWEEN STEP 3
AND STEP 5 FOR REDUCED OUTPUT GLITCH.
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 SELECT THE OUTEN BIT.
STEP 5: WRITE TO DAC CONTROL REGISTER. RELOAD
SEQUENCE AS IN STEP 3 ABOVE. THIS TIME
SELECT THE OUTEN BIT TO ENABLE
THE OUTPUT.
09225-073
Figure 51. Programming Sequence for Enabling the Output Correctly
CHANGING AND REPROGRAMMING THE RANGE
When changing between ranges, the same sequence as
described in the Programming Sequence to Write/Enable the
Output Correctly section should be used. It is recommended to
set the range to zero scale prior to disabling the output. Because
the dc-to-dc switching frequency, maximum voltage, and phase
have already been selected, there is no need to reprogram these.
A flowchart of this sequence is shown in Figure 52.
CHANNE
L
’S OUTPUT IS ENABLED.
STE
P
3: WRITE V
ALUE
TO THE DAC D
ATA
REGISTER.
STE
P
1:
WRITE
T
O CHANNE
L
’S DAC D
AT
A
REGISTER. SET THE OUTPUT
TO 0V (ZERO OR MIDSCALE).
STE
P
2:
WRITE
T
O DAC CONTRO
L
REGISTER.
DISABLE THE OUTPUT (OUTEN = 0),
AND
SET THE NEW OUTPUT RANGE. KEEP
THE
DC_DC BIT AND THE INT_ENABLE BIT SE
T
.
STE
P
4: WRITE
TO DAC CONTRO
L
REGISTER.
RELOAD SEQUENCE
AS IN STEP
2 ABOVE.
THIS TIME SELECT THE OUTEN BIT
TO
ENABLE THE OUTPU
T.
09225-074
Figure 52. Steps for Changing the Output Range