variable power supply required

This micromodule meets your electrical specs, and is truly a module (all passives inside

the package except for bulk capacitors:

https://www.analog.com/media/en/technical-documentation/data-sheets/8027fd.pdf

4A output current, 2.5V to 24V output voltage range, 7.5 to 60V input voltage range. 

The only compromise is that the output voltage is programmable via a resistor to

ground on the ADJ pin, a 12V out requires a >50K resistor, a 2.5V out requires a 

<500K resistor. This non-volatile digital trimpot:

https://www.analog.com/media/en/technical-documentation/data-sheets/ADN2850.pdf

could be the right way to implement this resistor to achieve your variable-voltage

requirement. It consists of two 250K trimpots, which will power up to a stored

setting in the on-board EEPROM, and can then be dynamically updated in 

time (w/o writing the EEPROM). Each trimpot has 1024 bits of resolution, so

together in series you should be able to get a 500K resistor with 11 bits of control. 

There could very well be a better fit to your requirements in the catalog,

so hopefully someone else will post with a better match.  There are

many modules that have on-board digital interfaces, but I couldn't

find one that met your 2.5V minimum output voltage (but it could

very well exist).  Also, if you're willing to go to a solution with 

external inductors, many options open up, but your "minimum

risk" requirement led me to believe you wanted a module.

Good luck,

This micromodule meets your electrical specs, and is truly a module (all passives inside

the package except for bulk capacitors:

https://www.analog.com/media/en/technical-documentation/data-sheets/8027fd.pdf

4A output current, 2.5V to 24V output voltage range, 7.5 to 60V input voltage range. 

The only compromise is that the output voltage is programmable via a resistor to

ground on the ADJ pin, a 12V out requires a >50K resistor, a 2.5V out requires a 

<500K resistor. This non-volatile digital trimpot:

https://www.analog.com/media/en/technical-documentation/data-sheets/ADN2850.pdf

could be the right way to implement this resistor to achieve your variable-voltage

requirement. It consists of two 250K trimpots, which will power up to a stored

setting in the on-board EEPROM, and can then be dynamically updated in 

time (w/o writing the EEPROM). Each trimpot has 1024 bits of resolution, so

together in series you should be able to get a 500K resistor with 11 bits of control. 

There could very well be a better fit to your requirements in the catalog,

so hopefully someone else will post with a better match.  There are

many modules that have on-board digital interfaces, but I couldn't

find one that met your 2.5V minimum output voltage (but it could

very well exist).  Also, if you're willing to go to a solution with 

external inductors, many options open up, but your "minimum

risk" requirement led me to believe you wanted a module.

Good luck,

Hi,

    Thanks for taking time and giving response. This looks ok. 

I don't want to add additional digital potentiometer on my board.

I have DAC which can give 4V FS.

As per datasheet range of RAdj should be from 56Kohm to 483Kohm.

RAdj=  56Kohm ( Vout 12V) and   RAdj=  483 Kohm ( Vout 2.5V)

Can you please tell me how to use this LTM8027 as a Variable output supply using DAC ? Is there any way to change output with the help of DAC ?

Regards,

Bitesh

See this application note for a starting point:

https://www.analog.com/media/en/technical-documentation/design-notes/add-margining-capability-to-a-dcdc-converter.pdf

I believe that the ADJ pin on the LTM8027 corresponds to the V_FB pin in

the application note, the RAdj resistor for the LTM8027 corresponds to

the R_bottom resistor in the application note, and an 499K resistor

in the LTM8027 corresponds to the R_top resistor in the application

note.  The main difference between the application note and your

design is that you have a voltage DAC and the application note

describes a current DAC. However, the steady state of the ADJ

pin should be the feedback reference voltage (which appears

to be 1.23V from the equation on page 9 of the data sheet), so

you should be able to use a simple resistor from the DAC output

to the ADJ pin as a voltage to current converter (or alternatively,

changing your design to add a current DAC).

This all said, it would be good for someone from ADI to chime

in with confirmation and suggestions. I'm taking my best guess

from reading the data sheet but I don't have hands-on experience

with the part.  Finally, the following two application notes, although

they deal with using alternate solutions, might have information

that would be of use to you.

https://www.analog.com/media/en/technical-documentation/tech-articles/Digital-Potentiometers-Enable-Fast-Linear-Adjustment-of-Switched-Mode-Power-Supplies.pdf

https://www.analog.com/media/en/technical-documentation/tech-articles/lt-journal-article/LTC2920-1_1203_Mag.pdf

Hi,

    I'm really grateful to you for taking time and responding. Got a starting point. Thanks.

Regards,

Bitesh