TPSM863252: Recommended Component Values

user6519235

Part Number: TPSM863252

Tool/software:

Hi,
I have two questions about recommended component value in the data sheet of TPSM86325X.
In table 8-2, R5 and R6 are selected so that the resistor flows 20uA when the output voltage is 2.5 V~10 V, and 60uA when the output voltage is 0.8~1.05 V.

1, Please tell me the reason why you chose 20uA and 60uA.

2, I am worried about malfunction due to noise, etc. Can the current be increased if the current consumption is not concerned?

Best Regards,

Hyodo

6 months ago

0 Andy Chen 6 months ago

TI__Mastermind 34045 points

Hi Hyodo,

No special reason, just select it to consume almost fixed power loss at no load condition.

You can use smaller resistor around 1K to 10K, but the Cff should be changed at sam eime.

0 user6519235 6 months ago in reply to Andy Chen

Prodigy 220 points

Thank you for your reply.
I understand that I can change the resistance value.

You note that Cff should be changed at sam eime(<-- same time, right?).

Please tell me how to calculate the optimum value of Cff.

Best regards,

Hyodo

0 Andy Chen 6 months ago in reply to user6519235

TI__Mastermind 34045 points

Hi,

Sorry for typo.

For example, assume the original recommended Rfbt=50K, Cff=20pF, the Rfbt will be lower if you decrease the Rfbb value below 10K, if new Rbft=20K, then Cff need to be 50pF to keep the same RC product value.

0 user6519235 5 months ago in reply to Andy Chen

Prodigy 220 points

Sorry for the late reply.
I guess from the answer you gave me last time, there is an inverse relationship between R and C, right?
However, in the datasheet "table 8-2. Recommended Component Values” does not.
Please tell me if there is a necessary calculation method.

Best regards,　

Hyodo

0 Andy Chen 5 months ago in reply to user6519235

TI__Mastermind 34045 points

For same Vout and Cout, the RC value should keeps similar value as recommended on data sheet if Rfbt is changed.

0 user6519235 5 months ago in reply to Andy Chen

Prodigy 220 points

Thank you for your reply.

I 'm going to generate Vout 5.5V and 3.7V by TPS863252.

And I'm trying to use the following resistance values.

(R5=220K, R6=27K) at Vout =5.5V
(R5=47K, R6=9.1K ) at Vout =3.7V

What is the value of Cff in this case?

Best　regards,

Hyodo

0 Andy Chen 5 months ago in reply to user6519235

TI__Mastermind 34045 points

Hi,

For 5.5Vout:

Effective Cout 44uF--100uF, Rfbt=220K, Cff=22pF

For 3.7V output:

Effective Cout 44uF--100uF, Rfbt=47K, Cff=68pF

0 user6519235 5 months ago in reply to Andy Chen

Prodigy 220 points

Hi,
Thank you for telling me the value of Cff.
If there is a formula, please let me know.

Best regards,

Hyodo

+1 Andy Chen 5 months ago in reply to user6519235

TI__Mastermind 34045 points

Hi,

No formula for this, just keep the new Rfbt*Cff product close to the recommended value on data sheet.

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TPSM863252: Recommended Component Values