ADAV4601 System Design Document
Confidential Information
Rev.1 August 2009
Analog Devices
Page 17
0V
Vref
(1.5V)
Charging Vref
Instantaneously
Vref charger circuit
0V
Vref
(1.5V)
Charging Vref
Instantaneously
Vref charger circuit
Figure 8: Vref Charger Circuit
This register write also powers up the iDAC buffer which is used to isolate the iDAC from the I/V converter. This
ensures that the current source drain voltages in the iDAC are fully charged up before they are applied to the
current to voltage converter. This ensures that the current source drain voltages follow the Vref charger circuit and
when transferred from the iDAC buffer to the current to voltage converter, they are both at the same potential,
which means that there is no sharp voltage transition at the output of the DAC. This register also enables the charge
iDAC function. When this bit is set to 1, this allows the instantaneous charging of the current DAC. This helps to
ensure that the DACs are powered up quicker.
34 0305 0100
This register write improves the DAC performance. It is therefore recommended that this be written to the part.
There should be a delay of at least 100ms after this write. This ensures that the Vref charger has had ample time to
charge the Vref voltage from 0V to 1.5V
34 008D 06A0
Once the Vref charger has charged the Vref voltage to 1.5V (after approximately 100ms). This register write disables
the Vref charger circuitry and enables the Vref voltage straight from the Vref core. See Figure 9 for more details.
Vref charger
Vref
Buffer
1.5k
Enable
Vref
From Vref core
Vref charger
enable
To current
amplifiers,
iDAC, I/V
converter etc
Vref charger
Vref
Buffer
1.5k
Enable
Vref
From Vref core
Vref charger
enable
To current
amplifiers,
iDAC, I/V
converter etc
Figure 9: Vref charger circuitry
There should be no DC level jump which would otherwise cause a noise on the output of the DAC. This register
write also disables the charge iDAC function. As the current DAC is now fully charged, there is no reason to have this
enabled anymore.
34 0000 001B
This register write now enables the Audio Processor for the ADAV4601. It also globally powers up all parts of the
ADAV4601 that have not already been powered up, this will include the SRCs, the PWM section, the ADC and DAC
engine (as well as all the ADCs which had not been previously powered up) and the audio processor. This register
write also enables the both the SRC1 and SRC2 for use.
Содержание ADAV4601
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