variable power supply required

Question

Hi, 
 
 In our one of the products we are using an adjustable Power supply. Output voltage of this power supply is controlled by on-board DAC (4V Fullscale). 
 This current module is from TI PTN78060W 
 We are looking for alternative options. 
 Can you please recommend me some modules from Analog Devices to replace the existing PTN78060W ? 
 Basically on-board we have 24V DC input and we want 2.5V to 12V DC output voltage with 3A output current. 
 We have on-board DAC which can be used to adjust the output voltage. 
 Also, we need a solution which requires less development efforts with minimal risks and part would be available easily to procure in large numbers for next 5-10 years. 
 
 Regards, 
 Bitesh

john-lazzaro · Accepted Answer

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)

john-lazzaro · Answer

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,

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variable power supply required