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TPS92692EVM-880: PROBLEM USING PWM DIMMING.

lanh tran
Prodigy 30 points
Part Number: TPS92692EVM-880
Other Parts Discussed in Thread: TPS92692

Dear Sir/Ms.

I have already bought a tool tps92692evm-880 from Mouser.com. So when testing, I have a problem with PWM Dimming.

In the user manual, Analog to PWM duty cycle dimming range: 1V to 3V of Vdim, and Direct PWM dimming range: 100Hz to 1Khz, connect shunt pins 1 and 2 of J6 and pins 1 and 2 of J7 in the tool.

I relate the tool to STM32F103C8T6 kit, mesure correct Vdim, and Direct PWM. But the output voltage range not change. It's still at 54V with Boost Configuration.

My input voltage range: 6V-100Ah battery.

I want the output voltage at 34.9-37V to load, but I can't do that.

Would you please give us some advice?

Best Regards,

Lanh Tran

  • 0
    TI__Mastermind 18890 points
    Hi Lanh,

    How are you connecting the LED load? Is the load tied at J3 output connector or J1? It should be going on J3 to run it in boost mode.
    With J6 shunting pin 1 and and pin 2 along with J7 shunting pin 1 and pin 2, you are in external PWM mode. What problem are you having with PWM dimming? Can we get a scope capture on the input PWM signal along with IMON signal?

    Thanks Tuan
  • 0 in reply to Tuan Tran74
    Prodigy 30 points

    Hi Tuan, Thank you for your feeback. 

    I use one led. Led voltage is 34.9-37V.
    Led current is 135mA
    I use J3 (Boost configuration), Shunt pins 1 and 2 of J6, pins 1 and 2 of J7 and extend PWM mode.
    I can't use the boost configuration for available led.
    PWM voltage maximum is 3V. PWM dimming: 1Khz
    Can you give a solution?
    I can't show you the signal of IMON, I don't have an oscilloscope

  • 0 in reply to lanh tran
    TI__Mastermind 18890 points

    Hi Lanh,

    I do not understand your statement 'I use J3 (Boost configuration)' then the next being 'I can't use the boost configuration for available led'.  Which one is correct?  Are you tying the LED load across J3 or where is the LED load tied to. 

    1.  What PWM'ing duty cycle are you running? 

    2.  What are you driving IADJ pin with in order to command the 135mA current because the default configuration is 356mA. 

    3.  Where are you measuring the output votlage to get 54V. 

    4.  Is there a data sheet for the LED that you are using to show it should be 34.9-37V?  What is the part number of the LED?  Where did this voltage come from because the TPS92692 is a current controller and it will drive the voltage to forward bias the LED to get the commanded current.

    We need to trouble-shoot to understand what you are trying to do and it's hard without an oscilloscope.  If you have a DVM then we can try this.  From the data below hopefully we can figure out what is going on.

    1.  Pull PWM to 100% duty cycle or 3VDC from a power supply

    2.  Measure the voltage on IMON with a DVM

    3.  Measure the DC votage on IADJ test point with DVM

    4.  Measure voltage across LED load.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 30 points
    I understand,
    "the TPS92692 is a current controller", Thank you so much.
    The part number of the LED is NTCWS024B-V3. The manufactory is Nichia Led.