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# TPS22990: Rise Time Calculation

Part Number: TPS22990

Hello,

My customer has question about adj. rise up time formula at TPS22990 & TPS22975.

Each devices are written about rise time (tR) in datasheet when Vbias is 5V.

My customer uses 3.3V of Vbias.

Do you have Calculation formula about rise time(tR) Vbias = 3.3V in each deveces?

Regards,

Taichi Nakamura

• Hi Taichi,

Do you have a specific VIN voltage for your use case with these devices? That way I can pull the data for your specific condition and come up with the appropriate equations.

Thanks,

Alek Kaknevicius

Hi Alek-san,

My customer may use VIN voltage 5V, 3.3V, 2.5V, 1.8V, 1.02V under the conditions of each IC.
Colud you tell me an equations at Vbias = 3.3V?

and, I have more question.
Is the equation for Vibas = 5 V only in the data sheet?
Is the formula changed by the Vin voltage?

Regards,
Taichi Nakamura

Hi taichi,

It is not advised to have VIN > VBIAS, so for the VIN=5V case, please connect VBIAS to 5V and use the equation in the datasheet.

Rather than giving a generic slew rate equation for all VIN conditions, I have broken down equations for rise time for each of the VIN voltages we have data for:

VIN = 3.3V: tR(us) = 0.038 x CT(pF) + 22.99

VIN = 1.8V: tR(us) = 0.021 x CT(pF) + 16.7

VIN = 1.05V: tR(us) = 0.0131 x CT(pF) + 11.85

Please keep in mind that these are estimates, and the numbers may change due to process or temperature variation.

Thanks,

Alek Kaknevicius

Hi, Alek-san

I have a more question.

① When TPS22990&TPS22975 use in Vbias = 3.3V & VIN=2.5V , Which can I use formula ?

② Is your answer last time common to both devices TPS22990 & TPS22975 ?

Regards,
Taichi Nakamura

Hi Taichi,

For VIN=2.5V, please use tR = 0.0289 x CT(pF) + 19.64. These equations are all for the TPS22990, I will post the equations for the TPS22975 soon.

Thanks,

Alek Kaknevicius

Hi Taichi,

For the TPS22975, we did not take the data for VBIAS=3.3V, but as an estimate I used VBIAS=5V and VBIAS=2.5V data to come up with the following equations for VBIAS=3.3V:

VIN=3.3V: tR(us) = 2.14 x CT(pF) + 136

VIN=2.5V: tR(us) = 1.65 x CT(pF) + 110

VIN=1.8V: tR(us) = 1.23 x CT(pF) + 88

VIN=1.05V: tR(us) = 0.773 x CT(pF) + 63.9

Again, please note that these are good for estimations, but process and temperature variation may cause some deviations from the equations.

Thanks,

Alek Kaknevicius

Hi, Alek-san

Thank you so much.

Although it is confirmation, ’TPS22975’ used in your formula is tR(uS) , In datasheet is SR (uS/V).

Is tR(uS) correct?

Regards,

Taichi Nakamura

Hi Taichi,

You are correct, these equations are for rise time and the one in the datasheet is slew rate. The slew rate equation applies for multiple voltages and the rise time equations are specific to the input voltage.

Thanks,

Alek Kaknevicius

Hi, Alek-san,

Thank you so much.

I see.

Regards,

Taichi Nakamura