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LMR14030: High Duty behavior at more than 24Vo

Kenji Ninagawa
Expert 4190 points
Part Number: LMR14030
Other Parts Discussed in Thread: TPS54361, , LM5175, LMR14050-Q1

Team,

 

Our customer is now working on TPS54361 for the spec : Vin=30-20V, Vo=24.5V, Io=10mA - 2A

However, TPS54361 DS describes;

"To reduce the losses of the small low-side MOSFET at high output voltages, the small low-side MOSFET disables at 24-V output and re-enables when the output

reaches 21.5 V."

So, when Vin is close to Vo, TPS54361 cannot work with high duty.

On the other hand, LMR14030 DS has no description about the similar contents of TPS54361.

 

Can LMR14030 work with high duty even when Vo > 24V ?

 

よろしくお願いします。

Thanks and Regards,

Metropolitan (Tokyo) Area FAE  Kenji Ninagawa

  • 0
    TI__Expert 5745 points

    Himax

    If the your Vin=20V~30V and Vout >20V, you can't use the LMR14030, because it's a BUCK. And the max duty cycle of the LMR14030 is 97% at 200KHz.

    I think you need to use a BUCK-BOOST for this application, such as LM5175.

  • 0 in reply to Vental Mao
    TI__Expert 4190 points
    No need of boost at Vin < setting Vo conditon, but only need of Vo = Vin as much as possible when Vin < setting Vo .
    So high duty work should be needed.
  • 0 in reply to Kenji Ninagawa
    TI__Expert 5745 points
    The LMR14030 can work in high duty cycle(0.97 at 200 KHz). But you need to save some margin in case the high current application.
  • 0 in reply to Vental Mao
    TI__Expert 4190 points
    what I want to know is the behavior at no load and/or very light load but not at high current.
    in case Vboot > around 3V (Boot UVLO), can LMR14030 achieve with 100% duty as same as TPS54361 ?
  • 0 in reply to Kenji Ninagawa
    TI__Expert 5745 points
    When operating with a low voltage difference from input to output, the high-side MOSFET of the LMR14050-Q1
    will operate at approximate 97% duty cycle. When the high-side MOSFET is continuously on for 5 or 6 switching
    cycles (5 or 6 switching cycles for frequency lower than 1 MHz, and 10 or 11 switching cycles for frequency
    higher than 1 MHz) and the voltage from BOOT to SW drops below 3.2 V, the high-side MOSFET is turned off
    and an integrated low side MOSFET pulls SW low to recharge the BOOT capacitor.
    You also can see the detail in section 7.3.4. and the LMR14030 can't reach to the 100% duty, the max is 97%