TPS65251 Unused channel

Toshio Ushikubo

Mastermind 9620 points

Hello,

Please advice how to process following terminals when I do not use back2 converter.

LX2

VIN2

BST2

EN2

RLIM2

SS2

CMP2

FB2

Best Regards.

over 11 years ago

0 Toshio Ushikubo over 11 years ago

Mastermind 9620 points

Hello,

Please anyone answer my question.

Regards.

0 Gregory Watkins over 11 years ago in reply to Toshio Ushikubo

TI__Expert 4005 points

Toshio-san,

For unused converters if PGOOD operation is needed:

•LX (output) - leave open.
•BST (input) - Leave open is ok, but is preferred to have at least a 1nF cap to ground.
•FB (input) - connect to 3v3 pin
•CMP (output) - leave open
•SS (input0) - connect to GND.
•RLIM (input) - output leave open.
•EN (input) - leave open
•VIN - Input, connect to VIN of other bucks

If PGOOD is not needed you can tie VINX and ENX to ground.

0 Toshio Ushikubo over 11 years ago in reply to Gregory Watkins

Mastermind 9620 points

Hello Gregory-san,

Thank you for your answer.

Regards.

0 Toshio Ushikubo over 11 years ago in reply to Toshio Ushikubo

Mastermind 9620 points

Hello Greg-san,

Please answer additional question from customer.
Your answer is “BST (input) - Leave open is ok, but is preferred to have at least a 1nF cap to ground.” in case of PGOOD is needed.
Customer does not need PGOOD, and want to reduce external parts as much as possible.

Please advice if leave BST terminal open is no problem or you still recommend 1nF capacitor to ground.

Best Regards.

0 Toshio Ushikubo over 11 years ago in reply to Toshio Ushikubo

Mastermind 9620 points

Hello Greg-san,

Please answer above additional question I posted Nov. 15 and following question from customer.

For V3V capacitor. Datasheet explain as follows.

Page 5: Connect a 3.3-μF to 10-μF ceramic capacitor from this pin to ground.

Please advice using 1uF capacitor for V3V terminal has problem or not.

Best Regards.

0 Wentao Xie over 11 years ago in reply to Toshio Ushikubo

TI__Prodigy 220 points

Hi,

if leave BST terminal open is no problem , 1nF capacitor to GND is not necessary. Because we use Bootstrap circuit for high side drive, BST is an output of internal LDO after a diode

If we don’t use the related buck converter, we can keep the BST terminal open.

0 Wentao Xie over 11 years ago in reply to Toshio Ushikubo

TI__Prodigy 220 points

Hi,

The output capacitor is critical in maintaining regulator stability, and must meet the required conditions for both

Minimum amount of capacitance and ESR. The minimum output capacitance required by the V3V is 3.3uF. Any decrease of the capacitance will affect the loop stability and transient response.

we don’t recommend to change it to 1uF.

0 Toshio Ushikubo over 11 years ago in reply to Wentao Xie

Mastermind 9620 points

Hello Wentao-san,

Thank you for your answer.

Best Regards.

0 Wentao Xie over 11 years ago in reply to Toshio Ushikubo

TI__Prodigy 220 points

Hi,

You are welcome! Please contact me if you have more questions about TPS6525X. My Email address w-xie@ti.com

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TPS65251 Unused channel