TPS73701 / Adjust start up time by CFB

S.Satoshi

Hi,

My customer plan to use TPS73701 but also want to adjust start up time. Then I think it can be done by adding CFB, is my understanding correct? I understand that CFB should be limited to 0.1uF.

Best Regards,

Sonoki / Japan Disty

over 9 years ago

0 Victor Salomon over 9 years ago

TI__Expert 3910 points

Hello Sonoki-san,

Yes, you are right, adding C_FB, increases the start-up time, the start-up time is divided into two stages that is: t_start-up= t_ref + t_C_FB

However, if your C_FB is big enough you can approximate your t_start-up to t_C_FB, where the t_C_FB charging time is determined by the resistance of R₁ and the capacitance of C_FB.

In this case, your start-up time will be given by thi equation: t_start-up≈ t_C_FB= 3 * R₁ * C_FB

For more information feel free to take a look at section 2.1 of application note "Pros and Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator (TI Document: SBVA042)", note that in this application note C_FB is referred as C_FF.

Best Regards,
Victor

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TPS73701 / Adjust start up time by CFB