How to extend Vin of a buck converter

[arikp]

Hi ,

I am trying to find a way to simply extend the input voltage range of a TPS563200 device or alike that will enable input from 4.5V-21V instead of 4.5V-17V ( the original range of the device).
First coms in mind is a FET feeding the VDD of the device by controlling its gate using zener at fixed voltage. Drain is at Vin and Source feeds the device VDD. The problem is that I lose the VGSth margin so I can only work minimum from 4.5V + VGSth Which is above the original minimum I need.

I am looking for a trick that can get me the original minumum voltage back and still keep the FET.

I am looking for a very simple solution.

Thanks for the helpers ,

Arik.p.

 

[malli_1729]

Just Check these..I didn't went much into details.....

**broken link removed**

**broken link removed** -> Page 33, Figure 3-17

http://www.ti.com/lit/an/slva119/slva119.pdf

 

[ravindragudi]

Looks like you are developing this for some automotive application. Isn't it? Can you let me know what is the minimum input voltage you need to work with and whats the output voltage is?
Also why this higher voltage range of 21V? Is it for some regulatory requirement? Does the unit has to be functional when the input goes beyond 17V?

 

[arikp]

Hello ,

This is meant to be used in a USB3.1 application.

Thanks ,

Arik.P.

 

[ravindragudi]

There is another option of looking into other buck regulators which can do the job. Example TPS54239EDDAR with same Eco mode from TI. It is 4.5V to 23V Input and 2-A output current.

 

[mtwieg]

Unless you're fine with significantly decreasing the power efficiency, you will have to find another IC.

 

[Anna Conda]

Or put in a P-fet LDO, such that the P-fet blocks the overvolts until the volts fall to an acceptable level whereupon the P-fet can be fully on to reduce losses. We have designed P-fet LDO's to work from 160v to 15V after which they are fully on to give only 50mV drop (down to 8V in)