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Original question:

TPS923655DMTREVM: TPS923655DMTR has wrong behavior if used in boost mode at 12V and does not sens a short circuit of the...

TPS923655DMTREVM: TPS923655DMTREVM tests with 12V and 24V, 500mA LED Bar @ 39Vf: currents involved and how to protect the TPS923655

PAOLO BOZZOLA
Intellectual 255 points
Part Number: TPS923655DMTREVM
Other Parts Discussed in Thread: TPS923655, TPS1653, TPS1663

Tool/software:

This new thread refers to the other thread:

<< TPS923655DMTREVM: TPS923655DMTR has wrong behavior if used in boost mode at 12V and does not sens a short circuit of the LED bar; OVP threshold voltage design is not explained >> which has received good suggestions by Lucia Gao.

The project needs more support before we can finalize the circuit design.

We want to be sure of the settings for the TPS923655 and how to usse an e-fuse to protect  the components in the supply path against short circuits of the output.

===============

EVM Setup: are below settings OK?

We are driving a new LED bar with 13 LEDS, 39Vf total, 500mA.

BOOST mode only for the TPS923655 

I have setup the EVM with the following component values:

  1. R7 = 0,4 Ohm  (fmax current 0,5A for the LED bar)
  2. R13 = 59K (FSET = 400kHz)
  3. R15 = 30K (TEMP foldback = 115°)
  4. R12 = 1.5M, R17 = 39K for OVP = 1.013V @ 40V (see Note 1)
  5. J3 = 1+2 (ADIM/HD = analog dimming 100%)
  6. J4 = 1+2 (EN/PWM = PWM dimming 100%)

Above references are for the new revision of the EVM (see attached file).

The EVM is powered either by 12Vdc or by 24Vdc.

Note 1: if the LED bar is disconnected, the output voltage before the chipset goes to fault becomes: 40V/1.013*1.45 = 57V which is safely below the 65V limit of the chipset. Hence the OVP resistor divider is correct.

These are the tests done till now with the EVM with above settings:

- Test of TPS923655 chip temperature at ambient 25°C temperature: around 52°C, powered by 12Vdc; less if powered by 24Vdc

- Test of TPS923655 chip temperature in chamber at 70°C temperature: below 100°C, powered by 12Vdc; something less if powered by 24Vdc

- In both cases the output current to the LED bar is stable, and the brightness of the LED bar does not decrease.

===============

The more help we need:

1) help to use the best solution for the e-fuse since this is needed in case there is a short circuit on J2

We would use one TPS16530 e-fuse for each TPS923655 chipset.

Questions:

  • is that a good choice? (we like simplicity)
  • Which is the suggested value for the R_ilim to pin ILIM of the e-fuse? (must be ok when the TPS923655 is powered by 12V with the 500mA LED bar connected)
  • We see high inrush current, so we want to have a smooth slew rate. Which capacitor suggestion for pin dVdT of the e-fuse?
  • How to set the e-fuse for permanent supply cut in case of short circuit (high current) detected?
  • Is it possible to have also a smooth shutdown when the applied power goes off? (we detected some current spikes when power off)
  • Any other suggestion is appreciated.

Note that the LED-Driver board under development does not have any microcontroller on board.

2) The LED Driver board will have two independent channels each based on the TPS923655DMTR, unique supply input (either 12V or 24V).

Question:

  • Can you suggest a solution for a unique e-fuse which can protect BOTH channels, instead of using one e-fuse for each channel?

That's all for now.

Attached: EVM schematic, possible choice e-fuse datasheet

 Best Regards

Paolo

(New_Version)_TPS92365xEVM_set-for-500mA@39V.PDF

tps1653.pdf

  • 0
    TI__Mastermind 30291 points

    Dear Paolo,

    Pls kindly let me check your question and get back to you during these days. Thank you!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    Intellectual 255 points

    Dear Lucia,

    News? 

    Thank you

    Best Regards

    Paolo Bozzola

  • 0 in reply to PAOLO BOZZOLA
    TI__Mastermind 30291 points

    Hi Paolo,

    Our field team is checking with Efuse team for the device selection. Thank you for your patience!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Mastermind 31711 points

    Hello Paolo,

    Welcome to E2E. Sorry for my delay in response.

    eFuse can be connected at the input of TPS923655. Find my response below. I have some follow-up equations as well

    • is that a good choice? (we like simplicity)
    • AJ: Yes, TPS1653 is a good choice but it doesn't have OVP. Similar device TPS1663 has OVP functionality. Do you need reverse current blocking or reverse polarity protection as well?
    • Which is the suggested value for the R_ilim to pin ILIM of the e-fuse? (must be ok when the TPS923655 is powered by 12V with the 500mA LED bar connected)
    • AJ:What's the max operating current expected for your application? Is it 1A when both channels connected at full load? 
    • We see high inrush current, so we want to have a smooth slew rate. Which capacitor suggestion for pin dVdT of the e-fuse?
    • AJ: Yes, inrush current can be controller through dVdT cap.
    • How to set the e-fuse for permanent supply cut in case of short circuit (high current) detected?
    • AJ: On event of short circuit eFuse will be OFF (latch off).
    • Is it possible to have also a smooth shutdown when the applied power goes off? (we detected some current spikes when power off)
    • AJ:How are you shutting off the now? Is it through any GPIO or VIN?

    Thanks 
    Amrit Jit 

  • 0 in reply to Amrit Jit
    Intellectual 255 points

    Dear Amrit,

    sorry also from me for the delayed response but CJB is closed, and I am answering to this thread remotely from home.

    Let's review what you have suggested.

    • Ok, we will use eventually the TPS16632 for e-fuse to protect the TPS923655.

    • The LED Bar driven by the TPS923655 drains 500mA @ about 40V (13 LEDs). I suppose that if we set the dVdT to have a very smooth powerup and inrush current (please suggest a good choice for the dVdT capacitor!) then the e-fuse current limit could be set for 2.2A limit. Do you agree?
      In fact...
      ...the LED Driver board can be powered either by 12Vdc or by 24Vdc. We cannot know which power rail will be used by the end user.
      So if powered by 12Vdc we have a 20W power needed by the LED BAR (40V x 500mA). Means about 1.7A from the 12Vdc and with a worst case 80% efficiency we have something like 2.1A input current at max brightness.
      If powered by 24Vdc  the LED BAR power remains the same 20W but the current to the TPS923655 will be half (less than 0.9A).
      So the 2.2A limit should be ok as well.
      What do you think????

    • The LED_Driver project is a dual channel board (so: 2x TPS923655 nad hence 2x TPS16632 ). Each channel is independent.
    • The LED_Driver board has no intelligence onboard: no microcontroller on board.

    • In case of fault, we want the LED_Driver stays disabled, until there is a power-off and then a power-on.

    • The shutdown is never controlled by a microprocessor (which is NOT onboard) but simply the LED Driver board will shut down when the user removes the power supply (24Vdc or 12Vdc).
      Any suggestion to make a smooth power down?

    That's all.

    Please let me know your feedback about above questions.

    Best Regards

    Paolo

  • 0 in reply to PAOLO BOZZOLA
    TI__Mastermind 30291 points

    Hi Paolo,

    Let me check and get back to you soon. Thank you!

    BRs

    Lucia

  • 0 in reply to PAOLO BOZZOLA
    TI__Mastermind 31711 points

    Hello Paolo,

    2.2A current limit seems right.

    For shut-down, when VIN is removed the input voltage at tps1663 will go below UVLO limit and device will turn OFF. Since you don't have micro-controller, you can keep the SHDN pin floating.

    Once schematic is ready. We can review that.

    Thanks 
    Amrit 

  • 0 in reply to Amrit Jit
    Intellectual 255 points

    Dear Amrit thanks,

    as soon as I have the schematic ready I will send it for review.

    Question: the project is confidential for my end customer. How can I send so it will not be disclosed to everyone?

    My best regards

    Paolo

  • 0 in reply to PAOLO BOZZOLA
    TI__Mastermind 30291 points

    Hi Paolo,

    You can send friendship with Amrit or send email to a-jit@ti.com  and lucia-gao@ti.com. Thank you!

    BRs

    Lucia