TPS53819A: Does it support 40A at 1.2V?

Amirhosein Akbari 

Yes, the TPS53819A can support 40-A loading currents with a 1.2V output with appropriately sized MOSFETs.

MOSFET current ratings are not typically intended to rate their expected current carrying ability in a switching application.  Rather, MOSFET current ratings are generally based on their DC current carrying ability.

For a 1.2V output, I would not recommend selecting the same MOSFET size for the top and bottom MOSFETs as their conduction and switching losses are very different.  In general, for a low output voltage like 1.2V, the low-side MOSFET will have a lower Rdson and higher current rating than the high-side MOSFET, but the exact balances would depend on other details of the design.

This article from 2010 covers some of the details on optimizing MOSFET selection in a BUCK converter

https://www.electronicdesign.com/technologies/power/power-supply/dc-dc-converters/article/21192283/the-j-k-method-a-technique-to-select-the-optimal-mosfet 

You may also want to use two single MOSFETs rather than a dual MOSFET like the CSD87350

If you are willing to consider an integrated converter, you may want to consider the TPS548D22 or TPS546E25, which integrate a 40A and 50A power-stage into a single package with a D-CAP constant on-time controller.

Hi Peter

Thanks for your reply

I am using PSpice simulation provided for it. It already has been set to 1.2V, but with increasing the load, the voltage drops. In the simulation, the switches are ideal. The weird part is that since in the datasheet it is mentioned to use CSD87350 which is mainly good for 20/25A. I am thinking maybe this controller is not designed for 40A, but for driving a switch with 40A capability which is CSD87350!

Please look this thread also. The TI experts mentions the controller max current is not more than 25A and that is why the output voltage drops!!

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/796920/tina-spice-tps53819a-tps53819a-start-up-voltage-cannot-be-changed-it-seems-the-output-voltage-is-been-fixed?tisearch=e2e-sitesearch&keymatch=TPS53819A#

Amirhosein Akbari 

Amirhosein Akbari said:

I am using PSpice simulation provided for it. It already has been set to 1.2V, but with increasing the load, the voltage drops. In the simulation, the switches are ideal.

Are you sure the switches are ideal and do not have Rdson?  I believe the switches in the PSpice model have an ON resistance modeled to represent the Rdson of the MOSFET.

The current limit of the TPS53819A is set by the resistor from TRIP to GND (35.7kΩ in the schematic from the simplis post to shared) and comparing the voltage across the TRIP resistor with the voltage drop across the low-side MOSFET (SW2) during the low-side ON-time.

This is described in more detail on page 18 of the datasheet - https://www.ti.com/lit/ds/symlink/tps53819a.pdf#page=18 

In the simulation, increasing the TRIP resistor or decreasing the on-resistance of the low-side switch should increase the current ability. 

Amirhosein Akbari said:

The weird part is that since in the datasheet it is mentioned to use CSD87350 which is mainly good for 20/25A. I am thinking maybe this controller is not designed for 40A,

The CSD87350 is just the MOSFET selected for the 12V to 1.2V @ 20A design example provided in the datasheet to demonstrate how to design a converter using the TPS53819A.  The TPS53819A can use a wide range of MOSFET for different applications, from very low currents, even less than 1A, upto 40A of current.

The 40A maximum recommended current is based on the MOSFET driver current capabilities 5V w/ 1.6Ω pull-up and 0.6Ω pull-down, and a 5V LDO capable of 150mA of average current.