LM3489-Q1: Quires on EVM for 100W PD

Nikhil Kakade

Part Number: LM3489-Q1
Other Parts Discussed in Thread: LM3489, TPS5450, LM61460, LMQ61460, LM61495

Hi,

We are designing a Dock that can deliver 100W PD source (20V, 5A max) in DFP mode and has USB3.2 HUB for downstream ports.

We have the below queries:

1. For our application TPS65987D looks suitable. We checked the TPS65897EVM board schematic. On the EVM board for input voltage step-down conversion, a LM3489-Q1 buck converter is used. I think EVM is capable of delivering 20V @ 5A (100W) but the buck converter is rated for Max 4A current.

So can we use this buck for 5A or can you suggest any other buck converter that will be suitable for 20V, 5A PD?

over 1 year ago

0 Nikhil Kakade over 1 year ago

Prodigy 40 points

Hi,

TPS5450-Q1 seems to be an alternative to the LM3489 buck.

but this does not have a Hysteretic PFET feature and the switching frequency is 500Khz.

Can we use this buck instead of LM3489?

0 Orlando Murray over 1 year ago in reply to Nikhil Kakade

TI__Mastermind 22299 points

Hi Nikhil,

The LM3489 uses a PFET which can achieve 100% duty cycle so that VIN≈VOUT.

The TPS5450 will have dropout voltage limitations when VIN approaches VOUT, the limitations are related to minimum off-time and maximum duty cycle. See equation 13 in the TPS5450 datasheet.

If you are doing 20VIN and trying to get 20VOUT the TPS5450 wont work.

The LM3489 is a controller, so as long as the PFET and diode can handle the temperatures associated with higher current then you should be able to use LM3489 for 5A.

Hope this helps,

-Orlando

0 Nikhil Kakade over 1 year ago in reply to Orlando Murray

Prodigy 40 points

Hi Orlando.

Thanks for the reply.

In our application input voltage is 24V so I think TPS5450 also works.

OR in TPS65897EVM LM3489 schematic block, PDS1040L (rated for 10A) diode and AON7403L (rated for Id: 8A(Ta)) PFET used.

both are rated for above 5A. So can I use LM3489? I can use another PFET with more Id (Continuous drain current) and lower Rds(On resistance) to reduce the heat generation.

And if we use the TPS5450, its switching frequency is 500Khz. Is it going to affect the output because of the LM3489 works with 1Mhz switching frequency?

I found one another buck controller LM25088 that looks suitable for our application.

I am not a power electronics guy so can you please guide us on which buck is better for our application?

0 Orlando Murray over 1 year ago in reply to Nikhil Kakade

TI__Mastermind 22299 points

Hi Nikhil,

Those are older devices, consider the LM61460 or (LMQ61460 with integrated capacitors for lower EMI).

LM61495 is also an option.

See appnote below:

https://www.ti.com/lit/an/snvaa33/snvaa33.pdf

Those device you mentioned are controllers, they require external FETs &or diodes, they're useful for high ambient temperature applications but are more complex to layout than the converters I mentioned.(integrated FETs).

Hope this helps,

-Orlando

0 Nikhil Kakade over 1 year ago in reply to Orlando Murray

Prodigy 40 points

Hi Orlando,

This bucks option sounds perfect.

Thanks.

0 Nikhil Kakade over 1 year ago in reply to Nikhil Kakade

Prodigy 40 points

Hi Orlando,

I found that there is a major stock issue with LM61460 and LM61495 buk converter IC.

Can you please suggest any similar ICs?

0 Orlando Murray over 1 year ago in reply to Nikhil Kakade

TI__Mastermind 22299 points

Hi Nikhil,

From what I can see the LM61460 is in transit and should be restocked soon.

-Orlando

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LM3489-Q1: Quires on EVM for 100W PD