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LM5119: how to set VCCDIS pin and DEMB pin?

Max Han
Intellectual 2260 points
Part Number: LM5119

Hi 

1. LM5119 is used in customer side, interleave buck, the output is 12V. so customer want that at start up, the internal VCC regulator is used, after 12V is stable, 12V is used to provide VCC power.

On LM5119 EVM, a diode from output to VCC is inserted. customer want to know how to set VCCDIS pin (pin 8)?

2. Diode Emulation Mode is not needed, so customer need to connect DEMB to VCC2. on EVM, this is a resistor R16, but this is no value shown.

do customer need this resistor or connect to VCC2 directly? if R16 is needed, what's the recommended value?

thanks.

  • 0
    TI__Mastermind 24075 points

    Hi Max, 

    1. The VCCDIS should be connected to a resistor divider, like R35, R36, C45 in the EVM schematic. 

    When Vout is above certain value (such as 10V), the VCCDIS pin voltage is above 1.25V and internal VCC regulator is disabled. 

    When VCCDIS pin voltage is below 1.25V, the internal VCC regulator is enabled. 

    2. If Diode Emulation Mode is not needed, DEMB pin can be connected to VCC directly or through a 0ohm resistor. 

    Thanks

    Qian