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TPS1H000-Q1: PWM behavior - current limit and Fault pin

Igor Orlovich
Prodigy 180 points
Part Number: TPS1H000-Q1


Tool/software:

Is there a link between the effective current limit and the duty cycle of a PWM wave fed into IN pin?
Using 4.75k CL resistor, I can get up to 140mA out of the part when IN is high.
As soon as I start PWMing the input the current limit scales down. Is that expected?
Here is an  example if I go from 88% to 87% duty cycle, my output (103mA max in this case) turns off:


 

And a secondary question- Fault pin appears to pulse, unless my off time is very short. Note that the output stays on in this case:




  • 0
    TI__Genius 12851 points

    Hi Igor,

    Getting more information, will get back to you by tomorrow EOD!

    Thanks,

    Rishika Patel

  • 0
    TI__Genius 12851 points

    Hi Igor,

    PWMing should not change the current limit. However, the external current limit accuracy is only applicable to overload conditions greater than 1.5 x the current limit setting. So, the device may be getting stuck in the linear region not the saturation region. The device also may be experiencing a thermal fault with the switching frequency like if you are turning off the device before it is completely on (please refer to turnon and turnoff delay times below).

    Thanks,

    Rishika Patel 

  • 0 in reply to Rishika Patel
    TI__Genius 12851 points

    Please also see section 4.1 in the following application note-adjustable current limit of smart power switches (https://www.ti.com/lit/an/slva859b/slva859b.pdf)- for more information on the linear and saturation regions. 

  • +1 in reply to Rishika Patel
    Prodigy 180 points

    Thank you. It appears part of the issue was using a programmable load. Even in constant resistance mode it would interact with the PWM control of the switch. Using resistors instead seem to make the part behave a bit more like expected. 
    Somewhat related, do you offer protected parts like this one but with ability to run at 20kHz and with both top and bottom side switches? The goal is to be able to generate a waveform at minimum load current

  • +1 in reply to Igor Orlovich
    TI__Genius 12851 points

    Hi Igor,

    Unfortunately, we do not have a high side switch that supports 20kHz switching frequency; the highest any of our devices go is 2kHz at a 50% duty cycle. However, as an alternative solution, a low side switch can be used for higher switching frequencies and a high side switch can be used for protection.

    Thanks,

    Rishika Patel