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TPS922055: Device usage

Hideki Hayashi1
Expert 8380 points
Part Number: TPS922055

Tool/software:

Hi team,

1. Does the TPS922055 work with 200kHz switching frequency, and dimming PWM is 20kHz. Is it able to have the output current PWM rising time and falling time shorter than 2us? I saw the user guide of EVM, the rising time is about 12us. What parameter cause it?

2. Below waveform at the datasheet it taken in 1.2MHz fsw, in this relatively high frequency area to operate, is there any consideration needed such as EMI and temprature? Also how much is efficinecy on this setting?

Best regards,

Hayashi

  • 0
    TI__Mastermind 30031 points

    Hi Hayashi,

    Thanks for reaching out! I'll get back to you early next week. Thank you!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Mastermind 30031 points

    Hi Hayashi,

    May I know customer and application or maybe could you pls send to my email (lucia-gao@ti.com) so that we can have offline discussion?

    For PWM dimming, usually with shunt FET dimming method, you can get the highest PWM dimming speed. For TPS922055, it implement PWM inductive fast dimming which means that there is improvement of it's dimming speed with IFD (Inductive fast dimming). As you can compare below comparison waveform (PWM and inductor current), with IFD method (as shown in the right figure), the error amplifier settle time is highly reduced. It will be good for accurate brightness control and wide dim ratio. Besides the inductor current settle time, there is also second order system response (non-pure square wave of the LED current) which is due to the filtering of the output capacitor. Thus, there are two factors that could have an effect on the response time: (1) Inductor current rise time which is related with inductance; (2) Second order system response time which is related with the output capacitor. Thus, if you would require shorter response time, I would suggest: (1) Lower the inductance to decrease the inductor current settle time; (2) Lower the output capacitance to decrease the response time.

    Hideki Hayashi1 said:
    1. Does the TPS922055 work with 200kHz switching frequency, and dimming PWM is 20kHz. Is it able to have the output current PWM rising time and falling time shorter than 2us? I saw the user guide of EVM, the rising time is about 12us. What parameter cause it?

    For EMI, it supports optional spread spectrum feature (TPS922055 is EMI friendly version) for better EMI performance. And for efficiency data, you can refer to datasheet 6-11 and 6-12 for reference. Or you can also apply for EVM board to do some measurement.

    Hideki Hayashi1 said:
    2. Below waveform at the datasheet it taken in 1.2MHz fsw, in this relatively high frequency area to operate, is there any consideration needed such as EMI and temprature? Also how much is efficinecy on this setting?

    BRs

    Lucia