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UC2843A-Q1: UC2843A-Q1_ISENSE

Ganesh V
Prodigy 120 points
Part Number: UC2843A-Q1

Am planning to use this Driver IC for our design, 

I need some clarification on this. When I'm doing WEBENCH with the UC2843A-Q1, there is an ISENSE pin in that circuit. I understand that it is used for sensing the current from the shunt resistor.

In addition, I can see a transistor switch circuit (Qsc and Rsc), but I'm not understanding the purpose of this circuit. Could you please clarify?

  • 0
    TI__Genius 15536 points

    Hi Ganesh,

    1. Isense. This pin is used to sense the current of the main switch of your converter. Rsns is the current sense resistor connected at the source of the FET. Rcs and Ccs set an RC filter at the current sense voltage. Due to the high dv/dt when the MOSFET turns on and the parasitic capacitor at the switching node, the drain current of the FET gets high peak currents at the beginning of the ON time. Rcs_Ccs filter attenuates those high peaks. Please refer to Figure 7.1 of Datasheet.

    2. Qsc and Rsc set a slope compensation for the current sense signal adding a portion of the oscillator ramp signal (RT/CT pin) to the current sense signal. In peak current mode control, when the steady state duty cycle is higher than 50%, the reference voltage for the PWM comparator needs to be sloped compensated. This will prevent any instability and improve noise immunity to the PWM comparator. Please refer to Figure 7.7 of Datasheet.

    If you have any further questions, please let me know replying to this thread.