TPS40304: TPS40304 design review and MOSFET alternative.

Sanjitsingh Rait

Part Number: TPS40304
Other Parts Discussed in Thread: CSD16340Q3, CSD17308Q3, , CSD13202Q2, CSD16301Q2, TPSM82866A

Hi,

I have designed the circuit from web bench power designer. Below is the attached snippet of my circuit.

Below is the reference snippet of web bench power designer circuit.

Please review the scheme and let us know your comments. We are using this part first time and do not want to make any chance of error.

Secondly, I am confused why M1 Mosfet drain current is 5A in power designer while I have designed the circuit for 6A output. So why 5A Mosfet used for switching.

Also, we have selected CSD16340Q3 for M1 and CSD17308Q3 for M2. Please let us know is this MOSFET selection correct?

Earliest response would be highly appreciated. Thanks

over 2 years ago

0 Peter James Miller over 2 years ago

TI__Guru 55000 points

Sanjitsingh Rait

Thank you for choosing the TPS40304 controller for your 5V to 3.3V @ 6A design. Since this is new for you, you may want to consider a Converter (Switch Controller with Integrated MOSFETs) or Module (Switch Controller with Integrated MOSFETs and inductor) rather than a controller solution. The higher level of integration will generally provide for a smaller solution size and simplified design process.

Looking over the schematic, I can offer a few suggestions:

1) Do not "Do Not Populate" the SS capacitor (C265) The TPS40304 needs this capacitor to control the ramp-rate of the output voltage during start-up.

2) Depending on your EMI / EMC requirements and layout, you may want to include some additional resistors to help control the turn-on and turn-off rates of the MOSFETs, which can cause ringing of the switching node. A "Boot Strap" resistor between Pin 6 (BOOT) and C263 (Boot Strap Capacitor) can be useful in controlling the rising slew-rate on the SW node. A "Switch Node" resistor between Pin 5 (SW) and the junction between C263, the Source of Q2 and the Drain of Q2 can be useful in controlling it's turn-off. Resistors in series with HDRV and LDRV are generally not recommended as they interfere with the sensing of the MOSFET gate voltages.

3) The CSD16340Q3 has a lower Rdson that I would generally recommend for a Control (High-side) MOSFET in a 6A application and would likely contribute more switching losses than a MOSFET with a higher Rdson. Can you share the MOSFETs that WeBench originally recommended?

0 Sanjitsingh Rait over 2 years ago in reply to Peter James Miller

Prodigy 30 points

Hi Peter James Miller,

Thank you so much for your support and review.

The recommended MOSFET by WeBench is CSD16301Q2 (for high side) and CSD13202Q2 (for low side). Drain current of high side MOSFET is 5A so I am confused whether we can use it for 6A application.

Please share your thoughts so we can finalize the circuit.

Also, it would be very helpful if you can suggest part number of Converter (Switch Controller with Integrated MOSFETs) or Module (Switch Controller with Integrated MOSFETs and inductor).

+1 Peter James Miller over 2 years ago in reply to Sanjitsingh Rait

TI__Guru 55000 points

Sanjitsingh Rait said:
The recommended MOSFET by WeBench is CSD16301Q2 (for high side) and CSD13202Q2 (for low side). Drain current of high side MOSFET is 5A so I am confused whether we can use it for 6A application.

The 5A "Package Limited Continuous Drain Current" is, in essence, the thermal RMS current limit. Since the MOSFETs in the switcher are not carrying continuous current, but switching, the RMS current on the MOSFET will be lower than the output current. Switching at 600kHz, the "ON" time will be on the order of 1μs. The MOSFET is rated for 85A pulse currents upto 100μs, so I would not worry about the high-side MOSFET tolerating 1μs pulses of 6A as long as the thermal power dissipation is acceptable. You should be able to check that in the WeBench analysis of the MOSFETs.

Since the CSD16301Q2 has only 2nC total gate charge, I would recommend reducing the SW to BOOT capacitor (C263) to 22nF - 47nF as it will not need the capacitive hold-up of 150nF to supply the 2nC needed by the small high-side FET.

NOTE: Since the TPS40304 uses the Rdson of the low-side FET to set the current limit threshold, any change in the low-side FET should be followed by a review of the ILIM resistor (R157) value to make sure the current limit is set appropriately.

Sanjitsingh Rait said:
Also, it would be very helpful if you can suggest part number of Converter (Switch Controller with Integrated MOSFETs) or Module (Switch Controller with Integrated MOSFETs and inductor).

If you use the WeBench Power designer - https://webench.ti.com/power-designer/switching-regulator and you enter your design requirements including Minimum and Maximum input voltage, output voltage, load current and ambient temperature, WeBench can recommend devices that are able to support your application.

On the upper left, is the option to filter by configuration: Controllers, Converters, and Modules.

If you are looking for the smallest possible solutions, look for modules or converters with 6-8A ratings.

If you are looking for the highest efficiency at full load to minimize maximum input current, a 10-12A rated converter or module will generally have the best efficiency at 6A.

You have a lot of options depending on any other needs you might have such as fixed switching frequency, enable, power good, etc.

0 Sanjitsingh Rait over 2 years ago in reply to Peter James Miller

Prodigy 30 points

Hi Peter James Miller,

Thank you so much for your valuable support.

As per your suggestion, I have selected a module which I think will be good to use due to reduced circuitry. It will also reduce the layout complexity.

The only instock option I could find was TPSM82866AA0SRDJR. Can you please have a look on below link. Only input-output caps and Rset is used. Do you have any suggestions or we use the circuit as it is suggest by WeBench Designer?

Link : https://webench.ti.com/power-designer/switching-regulator/customize/139?noparams=0

Thanks