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LM5152-Q1: Does this have pulse skip duration at least 40us before entering bpass operation? How about after bypass operatoin?

Yoshiki Ochi
Genius 9455 points
Part Number: LM5152-Q1

Hi team, 

Datasheet figure "Figure 9-18. PWM to Bypass Transition in CCM Operation" has "pulse skipping" duration before and after bypass mode. Considering LM5152-Q1, high side switch must be turned on in bypass mode. I understood as lower. Could you confirm if my understanding correct?

(1) Before bypass operation, VIN is really close to VOUT and tON < tON_MIN, then, pulse skipping mode starts. Pulse skipping mode is finished and transition to Bypass operation after 40us in OVP status. At least in this duration, pulse skipping mode should be exist before bypass operation. 

(2) In pulse skip mode, is high side FET turned off as well as low side FET?

(3) After Bypass operation, VIN may still be closed to VOUT and tON < tON_MIN, then pulse skipping mode happens. In the case of  tON > tON_MIN and no light load condition, pulse skipping mode may be not exist after bypass operation. 

Regards,
Ochi

  • 0
    TI__Guru 65390 points

    Hello Ochi,

    1. When the input voltage rises, the device operates in CCM, if it is too high for CCM, it goes to pulse skipping and then in bypass mode if VOUT is in OVP. Why do you think it needs to exit pulse skipping before going into bypass?

    2. As no energy shall come from VIN, both switches should be off, but we need to check on the EVM. Please give us at least until Thursday to get back to you.

    3. This is possible.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    TI__Guru 65390 points

    Hello Ochi,

    In Pulse Skip Mode, both MOSFETs are off.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    TI__Genius 9455 points

    Hi Brigitte, 

    Brigitte said:
    1. When the input voltage rises, the device operates in CCM, if it is too high for CCM, it goes to pulse skipping and then in bypass mode if VOUT is in OVP. Why do you think it needs to exit pulse skipping before going into bypass?

    What happen if its "VOUT" does not reach "OVTH" but "ton; on-time" is lower than "ton-min"? We need to 6~16V VIN condition and VOUT-regulation-target is 12V. What happen if VIN=11.7V and RT = 9.09 kΩ? Will be pulse skip mode observed eternally?

    Regards,
    Ochi

  • +1 in reply to Yoshiki Ochi
    TI__Guru 65390 points

    Hello Ochi,

    Yes, the part will operate in pulse-skip mode.

    Best regards,
    Brigitte