TPS40170-Q1: max current derivation

Alex Lanter

Part Number: TPS40170-Q1
Other Parts Discussed in Thread: TPS40170, TPS28225-Q1

What is driving the 20A max limit posted on the TPS40170 product page? Looking to use this chip for 25~30A and the only thing that seems to me to limit the max output current (of a synchronous buck converter to be clear) is the ILIM pin which is largely driven by RDSon of the low side FET. It seems to me if you select a low side fet with low enough RDSon that it should not be an issue. Does the MFR recommend use for loads above 20A? Any limitations?

over 6 years ago

0 Katelyn Wiggenhorn over 6 years ago

TI__Genius 11040 points

Hello Alex,

I will discuss your question with the product expert, and we will provide feedback.

Best Regards,
Katelyn Wiggenhorn

0 Samuel Jaffe over 6 years ago in reply to Katelyn Wiggenhorn

TI__Mastermind 25590 points

Alex,

You are correct that there is no hard limit to the maximum current that this part can control/supply. We spec it at 20A because of the IC's ability to drive the FETs. You can definitely find a FET with lower RDSon but that FET will most likely require a stronger driver.

-Sam

0 Alex Lanter over 6 years ago in reply to Samuel Jaffe

Prodigy 50 points

Sam,

Thanks for the reply. I will be considering that when designing to ensure the 300mA posted driver current is suitable. A follow on questions:

Is there any issue with running supply voltage at 5V for this chip but switching 2.5V? I've noticed on a few synchronous buck drivers there is a minimum power stage voltage that it can switch (usually around 3V - For instance PN: TPS28225-Q1)

-Alex

0 Samuel Jaffe over 6 years ago in reply to Alex Lanter

TI__Mastermind 25590 points

Alex,

Are you saying you'd like to supply 2.5V on VIN but 5V on VDD? Or 5VIN with 2.5VOUT?

Lower drive voltages will mean lower gate voltages which will mean the RDSon of the FETs will be higher which will hurt efficiency (and current capacity).

-Sam

0 Alex Lanter over 6 years ago in reply to Samuel Jaffe

Prodigy 50 points

Sam,

Essentially, 5V simply supplying power to the tps40170 (Vin) but chopping a 2.5V high power bus down to 0.85V. Reason being is the 5V is much lower power than the 2.5V bus I'm working with.

-Alex

0 Samuel Jaffe over 6 years ago in reply to Alex Lanter

TI__Mastermind 25590 points

Alex,

Oh I see. So this may not work since the IC uses the high-side FET for short-circuit sensing. You can definitely go through the datasheet or modify an evaluation board. I don't believe this will work without some careful consideration and additional circuitry but you're more than welcome to give it a go and let me know :)

-Sam

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TPS40170-Q1: max current derivation