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Original question:

LM5170EVM-BIDIR: I can not operate in buck-mode

LM5170EVM-BIDIR: problem of onboard 10V bias or improper jumpers setting?

PiotrP
Prodigy 40 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170

Dear Sirs!

I connected LM5170EVM-BIDIR to external devices (DC power supply) exactly as it was described in user manual with jumpers settings as suggested by Mr Youhao Xi here --> e2e.ti.com/.../756524

Unfortunately my LM5170EVM-BIDIR doesn't work with these settings (and any jumpers J4 and J21 combination). LED D12 is blind.

When I power the circuit from an external 10V source applied to pin J17-43(10V) with jumpers J4 and J21 open, the system works correctly.

Is it a problem of onboard 10V bias or improper jumpers setting?

Best Regards

  • 0
    TI__Guru* 78070 points
    Hi Piotr,

    The link to my previous post that you referred to is broken and I am not sure which one you actually referred to. Please show the complete link.

    It sounds like that you haven't enable the onboard 10V bias supply. Two ways to enable it:

    (1) you need populate R4, and close J1's pin 2-3 if 12V is present, or 1-2 if 48V present. This enables the onboard 10V. Use R4=100k.

    (2) Or, you can also supply 3.3V to J17 pin5, which is labeled EN on the silkscreen. Note EN label is next to the GND pin. The pin on the other side is pin5.

    Hope this helps.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Hi Youhao,

    The link to your previous post is here --> http://e2e.ti.com/support/power-management/f/196/t/756524#pi320995=1

    Method (2) works only when I use external 10V source (with J4 and J21 open). When I try to use onboard bias (with J4 and J21(2-3) closed), supplying 3.3V to J17 pin5 (EN) gives no effect (I know that GND pin6 is under EN pin5).

    Regarding method (1) - I will try to use additional resistor R4 100k and close J1 pin 1-2 (48V source), but what about jumpers J4 and J21? It should be closed or open in this case?

    Best Regards

    Piotr

  • 0 in reply to PiotrP
    TI__Guru* 78070 points

    Hi Piotr,

    J4 and J21 should be closed if you want to use the onboard bias supplies.  Please also refer to the schematic of the EVM.  The reason that I suggests R4 is to get an master enable signal (UVLO) from the EVM, so you don't need to provide an external UVLO command.

    Good luck!

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 40 points
    Hi Youhao,

    Unfortunately R4 didn't help. The only way to startup circuit is to use external 10V bias. Is it possible the onboard bias is broken?

    Best Regards
    Piotr
  • 0 in reply to PiotrP
    TI__Guru* 78070 points

    Hi Piotr,

    It should.  The idea is to provide >2.5V at the UVLO pin to enable the onboard bias supplies as well as the LM5170.  Please refer to the EVM schematic and trace the UVLO signal line. After installing R4, you also need to close J1's 1-2 or 2-3, depending on which power source is supplied, either the 12V or the 48V. 

    Once this is done, supply the power and check the onboard 10V, 5V and 3.3V bias supplies.  They should be all up.  If not, then the onboard supplies may be damaged somehow.

    Let me know if the issue is resolved.  I close this thread here but you can re-open by posting.

    Thanks,

    Youhao