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LM61495: how can we design with LM61495 to get 1~15V Vout

Hale Tan
Expert 3770 points
Part Number: LM61495

Hi team,

The data sheet has this description, and I'm a little confused.
 
If we want to get the output voltage from 1V to 15V. Can we tie Bias pin to output? Because the output has more than 12V, as the DS said, we need to tie this pin to GND. We are not sure how we to design with this device.
  • 0
    TI__Guru 50120 points

    Hello,

    Since your output voltage range regulates up to 15V, it is suggested to tie bias to GND.

    This will result in the internal LDO being supplied from the input.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 3770 points

    Hi Jimmy,

    thanks. But if we tie bias to GND, what will happen?

    And do you have any other suggestion which can be used in this application if LM61495 is not suitable?

  • 0 in reply to Hale Tan
    TI__Guru 50120 points

    Hi,

    Tying bias to GND will valid operation and device will work. There will just not be improved efficiency because the internal LDO needs to be powered from the input supply. If you externally power the bias pin with a lower voltage ie. 5V instead of from the input supply which is 16V or above, the system would have an efficiency improvement by around 1-2% since the internal LDO will have less conduction losses.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 3770 points

    Jimmy,

    So the customer need a new device which can meet his requirement: changing Vout from 1V to 15V without modify circuit. Please help give a suggestion.

  • 0 in reply to Hale Tan
    TI__Guru 50120 points

    Hello,

    What does the customer circuit look like?

    If the customer has already designed in the LM61495, then BIAS should be pulled to GND for this Vout (1V to 15V).

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 3770 points

    Hi Jimmy,

    The customer used DAC to control FB and this is very common in optical module. So they just want a circuit without modify circuit. And as I said, they need to adjust voltage from 1V to 15V.

  • 0 in reply to Hale Tan
    TI__Expert 3770 points

    Hi Jimmy,

    Below is the customer schematic:

    So as the schematic shows, there will be DAC to adjust output voltage. Could you please provide a solution about bias pin? The customer want to tie bias pin to external 3.3V. Do you have any suggestion?

  • 0 in reply to Hale Tan
    TI__Guru 50120 points

    Hello,

    I am not sure what the issue is here. The pin description states to tie BIAS to GND if there is no external supply.

    However from your schematic, it shows there is an external supply on BIAS (VDD3V3). 

    The schematic looks okay and the customer can use the BIAS feature in this configuration.

    It only becomes an issue if there was no external VDD3V3 voltage and customer tied BIAS directly to VOUT (VCC-TEC),which is not the case here.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 3770 points

    Jimmy,

    Jimmy Hua said:
    I am not sure what the issue is here.

    Please find my above description as input. The customer application is to give 1V ~15V voltage by adjust DAC and feedback PIN. The question is: how can we get a circuit with  LM61495 Vout 1V~15V.

    Jimmy Hua said:
    The pin description states to tie BIAS to GND if there is no external supply.

    This description is for above 12V output. If output voltage is below 12V,  DS suggest to tie to external circuit or output voltage. Is that right?

    Jimmy Hua said:
    It only becomes an issue if there was no external VDD3V3 voltage and customer tied BIAS directly to VOUT (VCC-TEC),which is not the case here.

    Just make sure, so this circuit can be used with 1V Vout or 15V Vout. Is that right?

  • 0 in reply to Hale Tan
    TI__Guru 50120 points
    Hale Tan said:
    Please find my above description as input. The customer application is to give 1V ~15V voltage by adjust DAC and feedback PIN. The question is: how can we get a circuit with  LM61495 Vout 1V~15V.

    The circuit customer is using to get 1V to 15V is correct. Injecting current into the FB will control the output voltage. There is no additional circuitry needed here. If you want more details please read app note (https://www.ti.com/lit/an/slva861/slva861.pdf).

    Hale Tan said:
    Just make sure, so this circuit can be used with 1V Vout or 15V Vout. Is that right?

    Yes the way they connect BIA to an external VDD3V3 rail is correct and okay. Again there is no issues with this connection because this is an external supply.