TPS54627: TPS54627 power up

user1359349

Part Number: TPS54627

hello

For current PCBA,i have used a TPS54627 and MPS' DCDC chip powered for CPU,but the power on sequence was not considered before design.

according the datasheet of CPU,the output of TPS54627 must be ahead of the MPS' output, but the MPS' chip can't adjust the output time(there is no SS pin,and the EN pin is fixed to Vin),so ,i want to

make the output of TPS54627 as fast as possible ,i want to change the capacitor of the TPS54627 SS pin,is there any limitation of the capacitance value?

for example,change the C392 from 8200pf to 100pf ,or smaller.

please give me your advice

thanks!

over 3 years ago

0 Yuchang Zhang over 3 years ago

TI__Mastermind 18510 points

Hi, the value you plan to use is too smaller, the biggest concern is short ss time will trigger big inrush cause OC happen. you can try it on your board and check inductor current and Vout.

And also I will check whether there is EVM can be used for checking.

Yuchang

0 user1359349 over 3 years ago in reply to Yuchang Zhang

Intellectual 430 points

hi Mr zhang

thanks for your reply,i have acrroded to your advise,tested the wave of the output after i had reduced the value of the SS capacitor,however,i can't see any difference from before,is there a reasonable range of the capacitance? thanks!

looking forward your reply.

0 Yuchang Zhang over 3 years ago in reply to user1359349

TI__Mastermind 18510 points

Hi, What value did you try?

Yuchang

0 Gerold Dhanabalan - Online Design Tools over 3 years ago in reply to Yuchang Zhang

TI__Genius 14455 points

Can you please confirm the value that you tried? If the issue is already resolved, can you please let us know?

Regards,

Gerold

0 user1359349 over 3 years ago in reply to Gerold Dhanabalan - Online Design Tools

Intellectual 430 points

hello

i'm sorry for the delay,i'm busy for other project these days,i had tried 4700pF,1500pF,680pF,there is no different from 8200pF,the test result as follow:

if i choose these value ,can the chip working stably?

thanks!

0 Yuchang Zhang over 3 years ago in reply to user1359349

TI__Mastermind 18510 points

For different Css, different soft-start time should be seen, you can cal by the equation1.

Attached pictures tested on EVM with 8200p/4700p/680p, which soft-start time is around 1.2ms/760us/110us, which represent smaller Css, smaller soft-start time.

You need check whether the Vout can start up normally with full loading for short soft start time, because smaller soft start time may trigger OC during start up. if can start up normally, that is OK to use.

Yuchang

The evm test is Vout not VCC, and Vout is 1.05V.

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TPS54627: TPS54627 power up