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Original question:

TPS92661-Q1: flash issue

TPS92661-Q1: flash issue

user5215762
Prodigy 120 points
Part Number: TPS92661-Q1
Other Parts Discussed in Thread: TPS92515, TPS92518, LM3409

Hi Sir,

We met an issue when using TPS92661 , the condition is as below,

The schematic is as below, when using 3 LED as series connection , there is no problem including communication interface(read write data) ,but when LED over 2 LED, the LED is flashing. we don't know why and need your help

The power of LED came from power supply

1). The target is driver 8 LED( PIN LED12(+)-LED10(GND), the other connected to GND  as datasheet 

2).CLK Freq. = 307kHz for Baud rate = 19200 bps

3).TPS92661 EN set high

4).check PWR bit = 1

5).write PCKDIV = 0x00

6).LEDON(addr 0Ah-0Eh) =1

7).LEDOFF(addr 2Ah-2Eh) = 1023

8).ENON(addr B0h-B1h) = FFh

8).ENOFF(addr B2h-B3h) = FFh

9).check Diagnostic reg. OK

10).PWM Freq. = 150Hz(DPWR2[2:0] 0b000,DDEC[1:0] 0b00)

The test appears as follows：

1、When controlling LED12（LEDOFF(addr 2Dh) = 10）,I found LED12 flashing;When controlling LED12（LEDOFF(addr 2Dh) = 1023）,LED12 lights up normally.

2、when LED over 2 LED, the LED is flashing?

  • 0
    Prodigy 120 points
    Hi，Sir
    Add some questions during the test：
    When controlling one LED separately (LED12_ON=0, LED12_OFF=100) and controlling 2 LEDs (LED12/11_ON=0, LED12/11_OFF=100) and controlling 3 LEDs (LED12/11/10_ON=0, LED12/11 When /10_OFF=100), the brightness of the LEDs is inconsistent. What is the reason?
  • 0 in reply to user5215762
    TI__Mastermind 28655 points
    Hello,

    If you current source is an off-line power supply it is likely there is a lot of output capacitance. If there is you will get large current spikes when shunting the LEDs. You can check this with a current probe or a series resistor to see if there is large current spikes. The TPS92661 needs a current source with little to no output capacitance to work correct.

    Regards,
  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points
    I have not heard back from you so I believe you may have solved the issue.
    The thread will close now but will reopen if you reply.
  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points
    Yes, we are using an external power supply, the output is connected to a capacitor, but after we remove this capacitor, it will burn out tps92661, why？
  • 0 in reply to user5215762
    TI__Mastermind 28655 points

    Hello,

    I don't know what you are using for an external supply so I cannot tell you what happened.  Is the capacitor you removed part of the power supply?  What is the power supply (do you know what circuitry is inside of the supply and how it operates?)?  The current source needs to be able to allow instantaneous voltage change as the switches in the TPS92661 open and close.  I would recommend you try using the TPS92515, TPS92518 or LM3409 from a voltage source to see how it works.

    The TPS92661 is controlling where current flows either bypassing an LED or letting current flow to it.  If it is getting damaged it is most likely what is driving it causing the problem.

    BR,

  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points
    Hi,sir
    Based on your suggestions, we have solved the above problems, thank you very much!
    However, during the test, we found that the PWM duty cycle and current in the TPS92661 are not linear, and the datasheet does not exhibit this relationship. What is the reason? If it is not linear, do you have this relationship checklist?
  • 0 in reply to user5215762
    TI__Mastermind 28655 points
    Hello,

    The TPS92661 either shunts the current around an LED or allows the current to go to the LED. The only thing I could see causing this from the TPS92661 side would be if the PWM rate is very high allowing the rise and fall time to influence the duty cycle.

    Have you measured the current going to the TPS92661 and the LED? Again, it only directs current to the LED or around it (shunting it). Also is there capacitance across the LED?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points
    Hi,sir
    I tested the TPS92661 alone to make an LED bright, and then tested the relationship between the LED current and the PWM duty cycle. This relationship I looked at is not linear, my last question is to ask this.No capacitor on the LED.
  • 0 in reply to user5215762
    TI__Mastermind 28655 points
    Hello,

    You need to look at the current going to the TPS92661. If the current source is trying to respond to the voltage changes you may be seeing overshoot or undershoot. The TPS92661 only directs current to the LED or Shunted around it. It doesn't modify the current.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 120 points
    Hi,sir
    Thank you. These problems have been solved.But there is a confusion at present, that is, the datasheet only gives the use of a single TPS92661, I currently design two chips, such as how to control the second TPS92661 instructions given?The first address is (ADR2/1/0) 0x0.The second address is (ADR2/1/0) 0x1.We look forward to your reply.
  • 0 in reply to user5215762
    TI__Mastermind 28655 points
    Hello,

    7.4.3 (bottom of page 21) and Top of page 22, Figure 27, shows communications connections for multiple TPS92661s.
    7.5.1.1 shows the write steps for TPS92661. Figure 38 flow chart shows how it accesses other 661s.

    Best Regards,