Post Go back to editing

# AD7266 VCC<->Vdrive not more than 0.3V apart

On Pin 31 "VDRIVE Logic Power Supply Input"
you wrote that AVDD/DVDD should not be more than 0.3V away from Vdrive:

" The voltage supplied at this pin determines at what voltage the interface operates. This pin should be decoupled to DGND. The voltage at this pin may be different than that at AVDD and DVDD but should never exceed either by more than 0.3 V. "

How can i do this when i have two separate LDO's for AVDD=DVDD=5V and Vdrive=3.3V ?
Or is it ok to just give not more than 10mA to the Pin Vdrive: like doing a 330Ohm Resistor in Series before that pin ?

Thank you very much
Kind Regards

Reto

• Vdrive cannot exceed AVdd/DVdd by more than 0.3V.  It can be lower than AVdd/DVdd at any time.

If Vdrive is 3V and AVdd/DVdd is 5V then everything is setup properly.  If Vdrive goes above 5.3V then you can turn on an internal protection diode and part will be in an invalid state.

• I have two LDO's one for digital 3.3V and one for 5V, for Starting up i can guarantee that 5V is first and if 5V is good 3.3V will be enabled.

But for power down i can not guarantee that 3V3 is off before 5V (or Vdrive+0.3V < VCC).

Is that a Problem or not ? because power sequencing makes the thing a lot more complex for the power down case.

--> current limiting ?

--> something else?

• Hi retti,

In the Abs Max section of the datasheet, Table3 is an implicit way to make sure power are correct. In the table, the Vdrive voltage range is dependent with DVDD and AVDD. This means that AVDD/DVDD must be power up first before Vdrive. With your set up, it is correct to power down the Vdrive first before 5V.

Regards,

Jonathan

• There isn't a power sequencing requirement.  If you bring down one LDO before the other, it should make a difference.  The 0.3V only is important during normal operation.

• This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

Thank you,