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TPS92515HV: driver chip has to be configured for dimming down to 0%.

rafy ks
Prodigy 60 points
Part Number: TPS92515HV
Other Parts Discussed in Thread: TPS92513, TPS92512, TPS92515

We are working on an LED dimmer circuit which supports DALI2.0 Interface. We already received the hardware and working on software only. LED driver circuit is based TPS92515HV and below is the circuitry

enter image description here

But the issue is LED is not switching off even if the control signal which is Iadj is 0. We tried shorting Iadj to GND and still, there is a current of 3.5mA through LED which makes LED on always unless power is removed. This will lead to non-complinace of DALI OFF command. The board is powered externally and we cannot control it and also we cannot afford any major component addition like relays to control power line to the driver chip. Is there anything to do with TPS92515HV configuration.??

  • 0
    Prodigy 190 points
    hi ,
    have you tried pulling the PWM pin low. I found that the device that I was using (TPS92513)needed the PDIM pin to be pulled to GND if I wanted the driver turning OFF completely. Check the section 8.3.11. of the TPS92515HV datasheet. This explains how to do it.
    hope this helps :D
    Mat
  • 0
    TI__Mastermind 25500 points

    Hello,

    Mathew is correct. The TPS92512 has a minimum duty cycle so even with analog adjust at 0V there will be a minimum current unless PDIM is pulled low. The TPS92515 can generally go a bit lower due to its topology (it isn't constant frequency like the 512) but it still has a minimum on time and a maximum off time which in effect still creates a minimum duty cycle which it will switch at even with IADJ at 0V. To get it to zero current you need to pull the PWM pin low.

    Regards,

    Clint

  • 0 in reply to Mathew Thomas
    Prodigy 60 points

    Hi Mat,

    Thanks for your reply. Yes,I have seen the section in datasheet that you have mentioned. I would try that and post the result here. 

  • 0 in reply to Clinton Jensen
    Prodigy 60 points
    Thanks for the reply Clint. I would try this. I have one more concern with this circuitry. This analog dimming works well above 3% dimming. but below 3% it starts flickering and found that voltage-current stability is not there below 3%. we were informed that they went to analog dimming after doing much experiment on both analog and PWM dimming and PWM dimming is more prone to flickering. I'm not sure whether they have tried shunt FET dimming. what is the actual reason behing the flickering when dimming is below 3% and how we can overcome this. Our new requirement is to go down to 1% without any performance issue.

    Thanks
    Rafy
  • 0 in reply to rafy ks
    Prodigy 190 points
    I think shunt fet will work
    I am driving two chains of leds with two external fets at the end of each chain
    Your micro would have to sequence or multiplex the chains so that the chain doesn't appear open circuit to the driver
  • 0 in reply to rafy ks
    TI__Mastermind 25500 points

    Hello Rafy,

    Are you using an output capacitor? If so what value? I have seen issues analog dimming without, or with insufficient, output capacitance. It depends on the LED's dynamic resistance, but when the current pulses get really small and the average current really low the output voltage can actually fall below the off timer voltage before the off timer charges enough. That can result in it going into max off time then switching ok for a bit and back into max off time. The result can be flicker. For this reason a decent amount of output capacitance is recommended for deep analog dimming. If you are already using one we can look into it further, but I have definitely achieved better than 1% analog dimming with this device with no issues.

    Regards,

    Clint

  • 0 in reply to Mathew Thomas
    Prodigy 60 points

    Hi Mat,Thanks for the suggestion 

    Thanks for the suggestion. I would check the output capacitance as Clint answered which would be the least change and then will go for shunt FET.

  • 0 in reply to Clinton Jensen
    Prodigy 60 points
    Thanks for the quick reply Clint. The above circuit is complete, only LED module is not shown. Could you point out the output capacitor there that you are talking about.
  • 0 in reply to rafy ks
    TI__Mastermind 25500 points

    Hello Rafy,

    I'm referring to C311. So you are using one, but you may need more than that for the deepest dimming. I would try increasing that to 4.7uF and see if that improves the range and gets rid of flicker.

    Regards,

    Clint