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TPS92611-Q1: LED driver as PWM high side switch

Scarlett Cao
Expert 4030 points
Part Number: TPS92611-Q1

Hi team,

Customer need a to build a PWM high side switch in theiir system powering off the 5V supply. When the output short to ground, the current increase will pull low the 5V supply so is not expected. Therefore they are thinking whether our LED driver can achieve the same goal. 

From their evaluation the maximum current is 98mA. Can customer send Rsns=1ohm,  input 5V, PWM frequency is 140Hz, load is 1kohm//10nF to ground.  Is the device output current and voltage also PWM? What is the duty cycle accuracy in this case? Could you help simulate the case?

My understanding is device is hard to regulate current, can the maximum current be limited to 98mA?

Thank you

Scarlett

  • 0
    TI__Expert 3560 points

    Hi Scarlett, 

    Regarding the customer requirements, they fit within the specifications of the device. Also consider the voltage dropout from SUPPLY to OUT, if you need 5V at OUT you will need to increase your input voltage. You should expect a ~0.5 W (5V * 0.98mA) power dissipation in the device once you short to ground, please reference the Thermal Information table in the datasheet to see how this will affect your thermal metrics. Finally please be aware of the transient period in which the capacitor conducts current once the switch is turned on.

    Is the device output current and voltage also PWM?

    • Not sure I understand the question. There is one constant-current output, PWM dimming is accomplished via PWM input dimming or supply dimming. Perhaps rephrase the question and I can provide better assistance.

    What is the duty cycle accuracy in this case?

    • Please see section 6.6 of the datasheet for the output timing diagram and timing specifications. There is a nominal 17 us delay on the PWM rising edge, and a nominal 21 us delay on the PWM falling edge given the conditions specified in the datasheet. Since your frequency is relatively low, the rising and falling times of the PWM will not play that much of an effect on the output current.  The current accuracy will be dependent on the accuracy of the SNS resistor as well as the internal accuracy of V(OPEN_th_rising/falling), which is specified in the electrical characteristics.

    Could you help simulate the case?

    My understanding is device is hard to regulate current, can the maximum current be limited to 98mA?

    • The output current can be set using equation 1 on page 11 of the datasheet

    Thanks,

    Jaron