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# LT8653S : How high a voltage can VOUT be, based on the Feedback Resistor programming.

Category: Hardware
Product Number: LT8653S

LT8653S : How high a voltage can VOUT be, based on the Feedback Resistor programming. Can VOUT after the inductor be 5.5VDC, for instance, or 4.0VDC?

Parents
• Hello,

• first of all the possible Vout depends on the available Vin (it's still a buck regulator)
• VREF for adjustable output is 0.8V, with this value the feedback resistors for your desired Vout can be calculated.
• On top the possible duty cycle may potential limit your desired Vout. This depends on your Vin/Vout ratio and the selected switching frequency

So four your given values of 5.5V or 4.0V: As long as you have a sufficient Vin available: no problem!

You will find more details in the datasheet (frequency selection, formulas etc)

Reply
• Hello,

• first of all the possible Vout depends on the available Vin (it's still a buck regulator)
• VREF for adjustable output is 0.8V, with this value the feedback resistors for your desired Vout can be calculated.
• On top the possible duty cycle may potential limit your desired Vout. This depends on your Vin/Vout ratio and the selected switching frequency

So four your given values of 5.5V or 4.0V: As long as you have a sufficient Vin available: no problem!

You will find more details in the datasheet (frequency selection, formulas etc)

Children
• Hello.

I would like to hook up to the question.

The datasheet of LT8653S does not include any information about output voltages higher that 3,3V and 5V.

It says only you can set the output voltages as fixed by D0 and D1 inputs, or set free the output voltage by feedback resistors using the 0,8V reference.

But there is nowhere written what maximum voltage I can set on both 3,3V and 5V outputs.

For example, Vin=24V. Can I set 12V on single or both outputs when I do not violate the Vin/Vout and frequency limits?

If yes, why it is not mentioned in the LT8653S datasheet? Most of datasheets contains the maximum output voltages which may be set by FB resistors.

If there is possibility to use 0,8V reference, and set different voltages than 3,3V and 5V on outputs, why there is no info about that?

If the LT8653S is designed to change voltage on both outputs and they're not fixed (in some other converters the outputs are fixed i.e. to 3,3V, 5V etc. and that is ok), wy there is no info about higher voltages?

In LT8650 for instance, there is maximum output voltage mentioned in the datasheet.

I almost selected the LT8653S to my project for 3,3V and 5V, but I need also 12V. I have the 24V supply rail in the project.

Thank you in advance for answer, I would appreciate it.

• Hello,

the datasheet reflects and focus on the small and space saving solutions by using fixed Vout with D0/D1 pins. I was not involved in the datasheet process, I work in field apps. When 24V are available 12V can be configured as output voltage with a resistor combination of 10k (bottom) and 140k (top). Please connect D0/D1 appropriately.

• Thank you so much Markus for quick reply.

It helped me a lot.