TPS54360: Schematic review

Kygo Cheng

Expert 6830 points

Part Number: TPS54360

Hi Team,

There is a good new that we DIN TPS54360

And there have one thing need your support!
Please help check this SCH, THX

over 3 years ago

0 Frank De Stasi over 3 years ago

TI__Guru 72525 points

Hello

What is the range of input voltage ?

What is the range of load current ?

What is the value of the inductor?

Thanks

0 Kygo Cheng over 3 years ago in reply to Frank De Stasi

TI__Expert 6830 points

Hi Frank

After discuss with customer , we have updated SCH & refer to attachment (L=33uH datasheet )!

And Io= 3A

1.Please help check this SCH, THX

2.2.Cause this case need design power sequence , how could I design & calculate THX

mss7348.pdf

0 Denislav Petkov over 3 years ago in reply to Kygo Cheng

TI__Mastermind 19891 points

Hello Kygo,

1. Comments on the schematic:

a. The input capacitor is only 100nF. This seems very low. The datasheet has 2x2.2uF as an example. Webench recommends 4.7uF.

b. The compensation component values and output capacitor value are close to what Webench recommends for this design. However, the inductor should be in the 3.3uH range. The part number mentioned in the schematic is MSS7348-333 which is 33uH. This will result in low phase margin with the existing compensation. Please recommend staying with 3.3uH.

2. In terms of sequencing and simulating - you can use webench or run a PSpice for TI.

Regards,

Denislav

0 Kygo Cheng over 3 years ago in reply to Denislav Petkov

TI__Expert 6830 points

Hi Denislav

Thank you for your feedback!

May I use R4 & C12 to be a RC delay ?

And the power sequence as below for your reference,THX

0 Denislav Petkov over 3 years ago in reply to Kygo Cheng

TI__Mastermind 19891 points

Hi Kygo,

I don't see an issue with RC delay on the EN pin, but one thing to note is the abs max rating on EN.

You should have a divider to bring the applied voltage on EN below abs max.

Please see the datasheet section on "7.3.7 Enable and Adjusting Undervoltage Lockout".

Regards,

Denislav

0 Kygo Cheng over 3 years ago in reply to Denislav Petkov

TI__Expert 6830 points

Hi Denislav

Thank you!

I'm calculating the startup time, can you help me confirm whether my calculation is correct?

TPS54360 after get 12V then will need 2.62mS(0.42mS + 2.2mS) to give Vcc5V

(T=R*C=R4*C12=2.2mS)

+1 Denislav Petkov over 3 years ago in reply to Kygo Cheng

TI__Mastermind 19891 points

Hello Kygo,

The built in soft start time depends on the switching frequency:

I wanted to highlight again that the abs max rating on EN is 8.4V. You should use a resistor divider from VIN to reduce the final applied voltage on EN below the abs max.

I think 100k top R, 20k bottom R, and 0.1uF Capacitor on EN should work. It would add about ~1.8ms delay to enable and then the soft start will add another ~0.8ms. I assume you want to get the 5V rail in 2.6ms and the soft start time is included in this duration.

Here is a calculator with these estimates.

calcs.xlsx

Standard disclaimer applies: https://www.ti.com/legal/important-notice-and-disclaimer.html

Regards,

Denislav