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TPS56A37: TPS56A37

Yuval Izhaki
Prodigy 200 points
Part Number: TPS56A37
Other Parts Discussed in Thread: DLP4500, TPS7A37, TPS56C231

Tool/software:

Hello

We design a replacement LED driver for the DLP4500 for delivering 10A LED current using the TPS56A37

The LEDs are connected in current loop and basic driver is working driving the LED with 10A current

We encountered issue with ON / OFF loading the driver (MOSFET switch) ,

When we draw a small amount of current (low intensity) the TPS56A37 switch to work in light load (ECO-MODE) condition cussing the LED to flicker

and when we increase intensity the TPS56A37 lock into light load (ECO-MODE) state and keep flickering,

We have some thought of loading the output of the TPS56A37 continuously,  but we are not sure whether its the right way, since we work in current loop and the equation on page 12 in the datasheet (for finding the load current to switch off ECO-MODE) use output voltage not current .

Is there is a batter way to disable the light load state and keep the TPS56A37 in full work state even when the load (LED) is disconnected or to find a load current to place the TPS7A37 in full work load?

P.S. current loop is done connecting the LED from the TPS56A37 output through a 25m ohm sense resistor and feeding the TPS56A37 FB pin with the voltage sampled by the sense resistor.  

 

  • 0
    TI__Genius 11175 points

    Hello,

    From my understanding, the ECO-MODE at light loads is causing the LED to flicker, so you would like continuous current throughout all loads (light and heavy). I took a look at the datasheet, and it seems TPS56A37 does not have an option to disable ECO-MODE. You would like to disable ECO-MODE at light loads correct? Would you be open to looking into alternative devices which offer an option to select FCCM or ECO-MODE?

    Please let me know

    Thank you,

    Calan

  • 0 in reply to Calan Elaya
    Prodigy 200 points

    Hi Calan ,

    Thank you for the fast answer,

    Yes we would like to disable or override the ECHO-MODE at light load

    We have a current design that use the TPS56A37, using a different switch regulator in a new design can't be taken under consideration at this time, due to request from our client to do the maximum with the current design (we already design and build a prototype)

    I believe adding a permanent load might solve the issue on the expanse of power consumption (OK from our side)- can that method solve the the problem , can you show me how to calculate the minimal load who can drive the TPS56A37 out of ECHO-MODE but will draw the minimum amount of current?

    regards

    Yuval   

     

  • 0 in reply to Yuval Izhaki
    TI__Genius 11175 points

    Hi Yuval,

    Thanks for providing this information. You are correct, since switching to an alternative buck regulator is not an option, we can utilize the FCCM mode in the TPS56A37 by keeping a constant continuous minimum current flowing through to prevent the ECO-MODE. In fact, I was able to test this on the bench and compare with Equation 1 on page 12 in the datasheet. My testing conditions were 14vin, 8vout, 500khz, 3.3uH inductor. The equation calculates the transition point to be around 1A of load current. This indeed matched by bench test results. I would recommend inputting your conditions in the equation to determine the minimum load that should be continuously drawn to prevent ECO-MODE.

    Hope this helps. If this helped solve your issue, please don't forget to click "This resolved my issue".

    Thank you,
    Calan

  • 0 in reply to Calan Elaya
    Prodigy 200 points

    Hi Calan

    Thank you for the replay , we are going to adopt this option and test it on our board.

    Can you please also recommend us a replacement for the TPS56A37 who have no start-up delay, can provide 10A@3.5V no ECHO-MODE or have a disable option for this mode (no external MOSFET)

    regards

    Yuval

  • 0 in reply to Yuval Izhaki
    TI__Genius 11175 points

    Hi Yuval,

    Regarding a potential replacement device, the TPS56C231 is another device that I support that should meet your conditions. The device capabilities land within Vin: 4.5-17V  Vout: 0.6V-6V,  and up to 12A of current. In addition, it has selectable FCCM or DCM mode, using the Mode pin resistor. If the TPS56A37 does not test well on your board, please reply to this thread with further questions. TPS56C231 is also a considerable option for your requirements.

    If this helps solve your issue, please don't forget to click "This resolved my issue".

    Best,

    Calan

  • 0 in reply to Calan Elaya
    Prodigy 200 points

    Hi Calan ,

    Thank you for the replay,

    The TPS56C231 can solve part of the issues  encountered with the TPS56A37,

    The other part (not mention earlier) is the soft-start time (min 1.8mSec) ,We need to switch ON/OFF the TPS56A37 at 4KHz.

    in the TPS56A37 we override it by floating the EN pin and putting the TPS56A37 enabled at all time + removing the Capacitor from the SS pin.

    is there is a better way to override soft-start time in the TPS56A231 ?

    regards

    Yuval    

  • 0 in reply to Yuval Izhaki
    TI__Genius 11175 points

    Hi Yuval,

    If you would like to implement the same procedure from the TPS56A37 into the TPS56C231, I do not see a potential issue. As long as the EN and SS operate the same in both devices. Attached below is a description of the SS for TPS56C231. Internal to the device by default, the SS is 1.2ms. You can adjust the SS time by externally connecting a capacitor on the SS pin. When EN is high, the ss charge current will begin charging that external SS cap. Below is also the equation to calculate the SS time and SS cap needed. 1.8ms does not seem impossible, although at some point, there will be a limit on the maximum SS time the device can do.

    Hope this helps answer your question.

    Thanks,
    Calan

  • 0 in reply to Calan Elaya
    Prodigy 200 points

    Hi Calan ,

    Thank you for the replay,

    Please let me elaborate,

    The SS in the TPS56231 have a minimum time of 1.2m Sec , We need to switch the TPS56A231 at 250u Sec (4KHz) ,

    Is there is a way to set the SS to start faster then 250u Sec or cancel the SS function?

    Regards

    Yuval

  • 0 in reply to Yuval Izhaki
    TI__Genius 11175 points

    Hi Yuval,

    Thanks for elaborating here. The minimum soft start time for TPS56C231 is about 1ms. I do not think it is possible for the SS for this device to be as minimal as 250us. I also have not heard of this device having the ability to cancel the SS function. You were saying that you were able to cancel the SS function in TPS56A37? Am I understanding correctly? please let me know, if so I can look into if TPS56C231 can do this.

    Thanks,

    Calan