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Original question:

TIDA-00779: Boost Inductor value

TIDA-00779: Output Capacitor and PCB Design

Sachin Kumar Bhoi
Prodigy 50 points
Part Number: TIDA-00779

I have few doubts regarding design

  1.  There is no film/ceramic capacitor in the output across output and MOSFET source to reduce high di/dt loop area and reduce MOSFET stress.  The VDS shared in the application note seems to be taken at low current. Though the output capacitor, MOSFET, diode area seems to be very optimized in the PCB, ESL of the capacitor is enough to cause voltage overshoot.
  2. In the PCB design, the control ground and power ground is connected at the output capacitor. I think it should be connected directly to the current sensor, better accuracy could be achieved and any ground offset/bounce  between two points might cause erratic behavior. 

What are your thoughts ?

  • 0
    TI__Intellectual 950 points
    1.  There is no film/ceramic capacitor in the output across output and MOSFET source to reduce high di/dt loop area and reduce MOSFET stress.  The VDS shared in the application note seems to be taken at low current. Though the output capacitor, MOSFET, diode area seems to be very optimized in the PCB, ESL of the capacitor is enough to cause voltage overshoot.
    2. In the PCB design, the control ground and power ground is connected at the output capacitor. I think it should be connected directly to the current sensor, better accuracy could be achieved and any ground offset/bounce  between two points might cause erratic behavior. 

    A: The ceramic capacitor added to DS will increase the switching loss, based on PCB optimized and test, we think voltage stress is trend off decision, in this TI design, it is not a concern.

    For question 2, connected at output capacitor can help eliminate the noise from the main switching  power stage, we have to be careful for ground connected.