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LMR14050-Q1: Hopping of the switching frequency

Huanfeng Ren
Prodigy 70 points
Part Number: LMR14050-Q1

Dear team,

My customer chose LM14050-Q1 to use as camera power supply chip.

They meets some issue and I want to ask you.

The input voltage range is 8.5~16V.

Output voltage is 8V.Loads current range is 1~2A.

Switching frequency is set to 1.8MHz by RT.

They find the switching frequency will jump to 180kHz when the input voltage reduce to less than 8.7V.

I want to know whether the phenomenon is normal? And what reason caused this?

Many thanks.

  • 0
    TI__Mastermind 27030 points

    HI 

    it is normal operation way, in datasheet 7.3.4, it describe the dropout work model, see below

    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.