TPSM82823A: Minimum on time

Hello Shunsuke,

TPSM82823A has DCS topology which is on-time based. However, the switching frequency of this topology does vary, and this variation is understood and controlled as explained in the App note shared with you.

The factors that causes the frequency variation at high duty cycle are the losses and a minimum off-time. To maximize efficiency, a minimum off-time is included to ensure that sufficient energy is delivered to the output because the energy stored in the inductor during the on-time is lower and maybe insufficient. This minimum off-time is set by the design and will have some tolerances as well. This is a control mechanism.

Thanks,

Febin

Hi Febin-san,

Thank you for the reply. I understood how minimum off time works in TPSM82823A. How about minimum on time? Could you please kindly investigate?

Best regards,

Shunsuke Yamamoto

Hi Febin-san,

Sorry for asking a question after clicking the solved button.

for the on time, 0.237ns at Vin = 5.5V and Vout = 0.6V based on the equation 1 on the datasheet regardless of any loads(light load, midium load and heavy load). Is this calculation correct? 

Best regards,

Shunsuke Yamamoto

Hi Febin-san,

Sorry, my calculation was wrong. 27.3ns is the on time at Vin = 5.5V and Vout = 0.6V.

Is this calculation correct?

Best regards,

Shunsuke Yamamoto

Hello Shunsuke-san,

Sorry for the delay. I was OoO until yesterday.

The calculation looks correct.

Thanks,

Febin

Hi Febin-san,

Thank you for the reply. It is good to know that the calculation is correct. However, what I asked to you is slightly different from what my customer wants to know.

My customer assumes there is a limitation of on time pulse duration and would like to know if the on time pulse duration of my customer's usecase has good margin compared with the minimum on time duration. If the on time duration of my customer's usecase is close to the minimum on time duration, it may violate the minimum on time duration and causes the wrong operation of TPSM82823A.

Best regards,

Shunsuke Yamamoto

Hello Shunsuke-san,

I am not sure if I understand completely. 

For the specific application conditions, a PWM switching frequency of typically 4 MHz is achieved with 27.3ns Ton. Only when the application conditions vary the Ton varies. And this minimum Ton is application specific.

Thanks,

Febin

Hi Febin-san,

Thank you for the reply. I don't think you understand my question correctly. Are there any limitations on minimum on time duration except for application conditions? When we don't consider the application conditions, we can make minimum on time to 0.0000001ns in my understanding.

Best regards,

Shunsuke Yamamoto

Hello Shunsuke-san,

How did you calculate 0.0000001ns?

Thanks,

Febin

Hi Febin,

Thank you for the reply. You mentioned there is no limitation of minimum on time duration.

Best regards,

Shunsuke Yamamoto

Hello Shunsuke-san,

There is a min Ton that needs to be set according to the application conditions (duty cycle) and that is 27.3ns.

I don’t understand the confusion here. Please let me know if a call is better to explain.

Thanks,

Febin