Resistance of EN about TPS54427/TPS54227

Takahiro Nishizawa

Genius 5575 points

Other Parts Discussed in Thread: TPS54427, TPS54227

Our customer uses the resistance of EN
as shown in the attached figure.

Question 1.

About TPS54427, does 225~900kΩ mean to RB?

And please tell me the recommended value of RB when VEN is 5V.

About TPS54227, does 220~880kΩ mean to RB?

And please tell me the recommended value of RB when VEN is 5V.

Question 2.

When VEN is 5V, does the IC have restriction about RA?

Question 3.

When customer uses TPS54427/54227 As shown in the attached figure, Can we use 1MΩ about RA?

And customer uses 1MΩ of RA, is there anything wrong?

Best regards,

Takahiro Nishizawa

Question of TPS54427 and TPS54227.pdf

over 7 years ago

0 Andy Chen over 7 years ago

TI__Mastermind 27115 points

Hi,

The Ren means the input resistance of EN pin, on cictomer circuit, you can consider that there is a resistor of 220K--900K pararreled with RB. then you can calculate the Ven based on this resistor network, make sure to use Ren-min 220K and Lowest Vin to set Ven-min > 1.6V. RA can be any value as long as the Ven>1.6V.

0 Vental Mao over 7 years ago

TI__Expert 5745 points

1）The 225~900K means the resistor connect to the EN pin to GND directly when the Ven=12V. For the divide resistor, you can set the RA and RB during the XXX Kohm when the Ven=5V
2) The IC is restricted by the voltage of EN pin(1.6V enable voltage), which is decided by the RA and RB.
3) We don't suggest to use such a big resistor which will introduce the resistor noise into the EN pin to false trigger the EN logic

0 Takahiro Nishizawa over 7 years ago in reply to Vental Mao

Genius 5575 points

Thank you for your answer!

I understood that 220~900kΩ means RB and we use resistance that voltage is over 1.6V.
In datasheet, RB is 220~900kΩ when Ven is 12V.
When Ven is 5V, must we use 220~900kΩ of RB?
and can we use 1MΩ of RB?

your answer : RA can be any value as long as the Ven>1.6V.
I understood this.

Best regards,

Takahiro Nishizawa

0 Vental Mao over 7 years ago in reply to Takahiro Nishizawa

TI__Expert 5745 points

the 200~900K is an internal resistor, you can't change it.
For the RA and RB, you can set them during XX Kohm to XXX Kohm ( such as Rb=10K, Ra=15K, Ven=5V). 1M is too big.

0 Takahiro Nishizawa over 7 years ago in reply to Vental Mao

Genius 5575 points

Thank you for your answer.
If we use 1MΩ, what kind of concerns do you have?

Best regards,

Takahiro Nishizawa

0 Vental Mao over 7 years ago in reply to Takahiro Nishizawa

TI__Expert 5745 points

Big resistor(1Mohm) will introduce the resistor noise into the EN pin which may false trigger the EN logic

0 Takahiro Nishizawa over 7 years ago in reply to Vental Mao

Genius 5575 points

Thank you for your answer!

Your answer,
For the RA and RB, you can set them during XX Kohm to XXX Kohm.

Do you know the maximum and minimum resistance that is not influenced by resistor noise?
I expect you to tell me your opinion.

Best regards,

Takahiro Nishizawa

0 Vental Mao over 7 years ago in reply to Takahiro Nishizawa

TI__Expert 5745 points

It's really hard to say the MAX and Min, it's an experience range.For the small resistor, which will increase the power loss. For big resistor, it's really hard to calculate the resistor noise . So we just don't recommend to use big resistor.

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Resistance of EN about TPS54427/TPS54227