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TPS7B7702-Q1: RDSON spec for Load switch

Lee, Sam
Expert 6045 points
Part Number: TPS7B7702-Q1

Hi team,

When using TPS7B7702-Q1 as load switch, could you please answer what is the max. Rdson spec?

Thanks,

Sam Lee

  • 0
    TI__Mastermind 23361 points

    Hi Sam, 

    For the load switch application, the TPS7B7702-Q1 is used in the switch-mode operation, correct? 

    When in switch mode, FB is connecting to GND. The Vout = Vin - Vdrop(@Iload) = Vin - RdsonxIload

    The electric table has the maximum dropout number for 100mA, which concerts to 0.5 / 0.1 = 5 Ohms Rdson. 

    At other load currents, there is no absolute maximum, but we know from Figure 7 in the datasheet that the dropout for this device is linear with the load current. I would suggest using max Rdson of 5 Ohms for any analysis.

    Regards, 
    Jason 

  • 0 in reply to Jason Song
    TI__Expert 6045 points

    Hi Jason,

    Thank you for your answer, Can I ask additional quesitons?

    -. The dropout curve in Figure7 is applied to both LDO mode and Switch mode. So, to output Vout = 7V @300mA/125C, below example is correct?

           a. LDO mode : min. Vin = Vout +Vdo = 7V + 1.4V = 8.4V

           b. Switch mode : Vin = 8.4V ??

    Thanks,

    Best Regards,

    Sam Lee

  • 0 in reply to Lee, Sam
    TI__Mastermind 23361 points

    Hi Sam, 

    -. The dropout curve in Figure7 is applied to both LDO mode and Switch mode. So, to output Vout = 7V @300mA/125C, below example is correct?

           a. LDO mode : min. Vin = Vout +Vdo = 7V + 1.4V = 8.4V

    --Yes, this is correct.

           b. Switch mode : Vin = 8.4V ??

    --Yes, but in switched-mode, the output is not fixed, so the Vout = Vin - Vdropout@Iload. If your Vin is moving higher to 9V, the dropout at 300mA stays the same, and the output will be 9V - 1.4V = 7.6V. 

    Regards, 

    Jason