LM5145EVM-HD-20A: Adjusting EVM Output Voltage

Kartavya Agarwal

Part Number: LM5145EVM-HD-20A
Other Parts Discussed in Thread: LM5145, LM5146-Q1

Hi,

I am considering buying a few LM5145EVM-HD-20A boards to test my application. However, the user guide of this EVM says that the output voltage is regulated at 5V. Can I adjust the output voltage of the EVM to 12V or 24V in any manner?

If this is not possible, could you please suggest similar buck converter EVM boards that have the similar Power rating, Input voltage specification, and adjustable Vout to 12V or 24V?

As a result, my requirement need is as follows:

Vin range: 24V - 72V (range in flexible but Vin,max should be at least 60V)
Power Output: 75W - 150W (any board in this range is good enough)
Vout: 5V, 12V, and 24V (It would be great to have one board with adjustable Vout channel that can be configured to 5V, 12V, or 24V. If this is not possible, 3 different boards will also suffice)

Could you please suggest any TI EVMs that can meet this requirement?

Sincerely,
Kartavya Agarwal.

over 3 years ago

0 Timothy Hegarty over 3 years ago

TI__Mastermind 49207 points

Hi Kartavya,

Try using the LM5146-Q1 EVM - this is effectively the same controller as the LM5145. The EVM is setup for 12V/8A/400kHz and uses 100V FETs suitable for your max Vin of 72V. To adjust Vout, just change the inductor, output caps and feedback/compensation as needed. You can use the quickstart calculator to assist with component selection.

Regards,

Tim

0 Kartavya Agarwal over 3 years ago in reply to Timothy Hegarty

Intellectual 500 points

Hi Timothy,

Thank you for your prompt response. Would you happen to know of any other options that could also provide me with a 24V regulated output voltage?

0 Timothy Hegarty over 3 years ago in reply to Kartavya Agarwal

TI__Mastermind 49207 points

Not in terms of EVMs, but it should be easy enough to modify the LM5146-Q1 EVM if needed. Also, take a look at the 24V output apps example in the LM5145 datasheet.

0 Kartavya Agarwal over 3 years ago in reply to Timothy Hegarty

Intellectual 500 points

Got it. I read through the data sheet for the chip and it seems like the output voltage set-point can be set using Rfb1 and Rfb2, which form a resistive divider network. However, I couldn't find an equation in the datasheet to precisely tell me how to do so to decide the resistor values. Is it something obvious that I'm missing or could you help me out here?

0 Timothy Hegarty over 3 years ago in reply to Kartavya Agarwal

TI__Mastermind 49207 points

It's simply a resistor divider from Vout to the FB voltage of 0.8V. The equation is in Table 5. Also, you can use the Excel quickstart calculator in the product folder to assist with component selection.

0 Kartavya Agarwal over 3 years ago in reply to Timothy Hegarty

Intellectual 500 points

Got it, thanks. Also, can I use the TRIM input pin on the EVM to adjust the output voltage digitally, perhaps through a micro controller?

0 Timothy Hegarty over 3 years ago in reply to Kartavya Agarwal

TI__Mastermind 49207 points

Hi Kartavya,

The adjustment depends on the current injected into the FB node. Typically, a PWM signal from the MCU is averaged with an RC filter to create an adjustable voltage that is applied to the TRIM pin.

Regards,

Tim

0 Kartavya Agarwal over 3 years ago in reply to Timothy Hegarty

Intellectual 500 points

Got it, so if I want to set the output voltage to 5V, giving it a PWM signal with an average voltage of 5V through an RC filter would suffice in that case?

However, an MCU cannot source more than 3.3V, so how could I achieve this with only an MCU? Is there something fundamental I'm missing and could you direct me to any literature that explains how to use the TRIM pin on this EVM?

0 Timothy Hegarty over 3 years ago in reply to Kartavya Agarwal

TI__Mastermind 49207 points

You need a PWM signal from the MCU with an adjustable duty cycle. Then the average value can control the current injected into FB to facilitate Vout adjustment.

Regards,

Tim

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LM5145EVM-HD-20A: Adjusting EVM Output Voltage