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Put into shutdown mode LP3856

Anton Evdokimov
Prodigy 30 points
Other Parts Discussed in Thread: LP3856
I need to use the scheme with LP3856: Input voltage is 6.5 V. The output voltage is 4.5 V. It is possible to translate in Shutdown mode using a microcontroller, which is powered by a 3 V. Are there any features of a given scheme.
Has anyone used such schemes?
  • 0
    TI__Mastermind 22610 points

    " ... The output voltage is 4.5 V. It is possible to translate in Shutdown mode using a microcontroller, ..."

    Since there is no version of LP3856 that is set for Vout of 4.5V, I will presume that your question here is regarding the feasibility of creating the 4.5V Vout by Pulse Width Modulating (PWM-ing) the /SD pin on a LP3856-5.0.

    This is not practical with LP3856. Taking the /SD pin low (i.e. Shutdown) disables all internal circuitry biasing, in ordered to get the absolute minimum Ignd current in Shutdown Mode. When /SD pin goes back high (i.e. Enabled) a finite about of delay time is needed to get all of the internal circuitry re-started.

    The undefined start-up delay time, plus no effective control loop, plus no ensured specifications for the /SD pin minimum required high (ON) and low (OFF) times for reliable operation make this unlikely to succeed.

    Far better solution would be to use a real SMPS Using. WEBENCH® Designer found on the www.ti.com home page can help with the selection process.