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I am designing an SMPS circuit and I am using a ready SMPS controller. In the datasheet, the ADP2303 Datasheet input range is given (3-20V) ± 1.5% output accuracy over temperature Output voltage down to 0.8 V, .What is the maximum voltage it can provide in this case?

In practice I use an ldo after smps because I will be feeding a sensitive adc. In this case, ldo will suppress ripple in the SMPS output with the psrr value. I will get 5.0 V from the LDO output ldo voltage dropout is lower than 0.2 V (for 1 amp). In this case, I want to feed the ldo input with a value such as 5.5 V. I will do this with SMPS output. Can the output of this SMPS be set to 5.5 V? What can be the maximum output voltage? I didn't see any specifications.

The output voltage circuit examples given are up to 5 Volts in datasheet . I thought I would ask the community before making mistakes SMPS controllers can generally provide a voltage slightly below the supply voltage. (Theoretically, the mosfet hold on time will increase)

enter image description here

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  • \$\begingroup\$ All info seems to be in the datasheet. If I'm reading it correctly then the maximum feedback voltage is 5.075 for the 5V part. Why must your ADC have 5V as reference though? We often pick a lower reference like 4.096V then divide inputs accordingly. (The magic number 4.096V giving a nice 1 to 1 correspondence with 12 bit ADC resolution 4096.) \$\endgroup\$
    – Lundin
    Commented Apr 18 at 9:40
  • \$\begingroup\$ @Lundin thats not for VREF ,its for VDDA supply \$\endgroup\$
    – Electronx
    Commented Apr 18 at 9:44
  • \$\begingroup\$ @Electronx Ok but most ADCs handle a supply close to VREF though? Btw an alternative to LDO is to use a "shunt voltage reference" which is basically a glorified, high precision zener diode. Lower dropout. \$\endgroup\$
    – Lundin
    Commented Apr 18 at 9:46
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    \$\begingroup\$ Read page 16 of the data sheet for the formula for max output voltage \$\endgroup\$
    – Andy aka
    Commented Apr 18 at 9:48
  • \$\begingroup\$ @Lundin Texas instruments and analog devices have many articles. They usually feed an ldo after smps to AVDD for adc .THE ADC that I use has 4.096 V internal reference. \$\endgroup\$
    – Electronx
    Commented Apr 18 at 9:49

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A couple of points to take note of here: -

  • Running the output of the LDO regulator close to its input voltage will likely produce a lot of noise on the regulator output hence, your 5 volts will be noisy and this will be reflected in the conversion results from the ADC
  • Voltage references are usually much less noisy and generally much more stable that any analogue voltage regulator

Page 16 of the data sheets gives you what you need regards a formula: -

enter image description here

The formula looks simple enough and, I see in your comments you have calculated 11.265 volts. So, I would aim to provide more input voltage to the LDO regulator in order to reduce output noise (if you don't want to use a voltage reference).

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  • \$\begingroup\$ Normally, I set it to 5.5 volts at the input of the (TPS7A91 )ldo (smps output). Is it better to draw 6 volts? \$\endgroup\$
    – Electronx
    Commented Apr 18 at 13:30
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    \$\begingroup\$ @Electronx look at the table on page 5 for output noise and you'll see that they have chosen a 1 volt higher input voltage than output voltage. Look at the graphs on the following page (particularly figure 4) and notice how much the PSRR improves with a higher input voltage. So, yes, it's far better at 6 volts. If we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Commented Apr 18 at 17:32

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