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# TPS7A24: About individual limit of R1 and R2

Part Number: TPS7A24

Hi Team,

We found “R1 + R2 ≤ VOUT / (IFB × 100)” in datasheet.

However, we would like to know the individual limit of R1 and R2 because use the following condition.

Could you please let us know if you have any concern for the following resistor values?

[Our conditions]

R1 is 1Mohm

R2 is 120kohm

Target VOUT is around 11.5V

*We would like to use large resistor because decrease the consumption current.

Regards,

Hide

• Hi Hide,

The nominal IFB current is 10nA so with R1 = 1Mohm and R2 = 120kOhm we have

11.5V/(100*10nA)= 11.5Mohm

Since your solution has R1+R2=1.12MOhm  is meeting the limitation highlight in equation 3:

The reason for this constraint on the feedback resistors is simply that we like to see the current leakage through R1+R2 be strong enough to swamp out any leakage into the FB pin as this could impact output regulation accuracy.

John Cummings 蔣康明
Texas Instruments 德洲儀器
Johncummings@ti.com

Thank you,

Hi JCHK-san,