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LM5177: How the LM5177 work?

Rock Shao
Expert 2995 points
Part Number: LM5177

Hi Team,

Ti's 4-switch H-type BUCK-BOOST control IC LM5177, if the circuit operates in BOOST mode, how does it keep the upper switch of BUCK on?

When measuring the waveform BUCK, the lower switch is OFF and the upper switch is ON.
If the charge pump is used, the lower switch must be turned on to charge the capacitor, but the measured waveform is not turned on. Thanks
  • 0
    TI__Expert 3260 points

    Hi Rock,

    Thanks for reaching out. If you look at our document "Basic Calculations of a 4 Switch Buck-Boost Power Stage", you can find the following figure:

    The 'classical' SMPS modes are then achieved by keeping certain switches open/closed, and switching the other switches. 

    If the device is in buck mode, SW2 is kept closed, SW4 is kept open, and SW1 and SW3 are switching, operating like a synchronous buck converter.
    If the device is in boost mode, SW1 is kept closed, SW3 is kept open, and SW2 and SW4 are switching, operating like a synchronous boost converter.

    Thank you and best regards,
    Bryan