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TPS54202H: About 100% on duty cycle and the actual maximum on duty cycle.

Kazuya Nakai59
Guru 21595 points
Part Number: TPS54202H
Other Parts Discussed in Thread: TPS54302

 Hello guys,

 One of my customers is considering using TPS54202H for their next products.

 They found the following description on page 11 in the device datasheet (SLVSDG7).

"7.3.11 Bootstrap Voltage (BOOT)
The TPS54202H has an integrated boot regulator and requires a 0.1-μF ceramic capacitor between the BOOT
and SW pins to provide the gate drive voltage for the high-side MOSFET. A ceramic capacitor with an X7R or
X5R grade dielectric is recommended because of the stable characteristics over temperature and voltage. To
improve drop out, the TPS54202H is designed to operate at 100% duty cycle as long as the BOOT to SW pin
voltage is greater than 2.1 V typically."

 They want to know how to achive 100% ON duty.

 Could you please tell me the way or any reference schematic for 100% duty?

 Also could you please give me your reply for the following question?

 What is the maximum ON duty or the minimum OFF duty (or time)  in normal operation of TPS54202H?

 Because the customer want to know what input voltage is needed to output 15V. 

 Your reply would be much appreciated.

 Best regards,

 Kazuya. 

  • 0
    TI__Expert 4035 points

    Hi Kazuya,

    TPS54202H could not support truly 100% duty cycle. When the bootstrap voltage is down to 2.1V, the low-side FET will be forced ON to charge the bootstrap cap.But it should be very near to 100%. Anther question is the Rdson in the high-side FET, the Rdson is influenced by the thermal, thermal is based on the output voltage and current. Also the DCR in the indutor and parasitic resistance on the board have voltage drop. So it would be a complex question for what the minimum input voltage is needed to support output 15V. I suggest to do the real test on your customer board.

  • 0 in reply to Ryan Hu (BSR-MV)
    Guru 21595 points

     Hi Ryan,

     Thank you very much for your reply.

     Could I ask you an additional questions as the follow?

     Q. The customer will connect 4 cell Li-ion battery (10.8V~ 16.8V) to TPS54302 input.

         I know TPS54302 can't keep 15V when the battery voltage is less than 15V.

        But I think TPS54302 continues near 100% operation without switching turning off even if the input voltage is less than 15V.

        And the device switching is stopped when the input voltage goes down to UVLO setting voltage.   

         Is my understanding correct?

     Thank you again and best regards,

     Kazuya.

      

  • 0 in reply to Kazuya Nakai59
    TI__Expert 4035 points

    Hi Kazuya,

    Yes, your understanding about the VIN UVLO is right. And you can also adjust the VIN UVLO by configuring the EN resistor network.

  • 0 in reply to Ryan Hu (BSR-MV)
    Guru 21595 points

     Hi Ryan,

     Thank you for your reply.

     It is very helpful for the customer and me.

     Thank you again and best regards,

     Kazuya Nakai.