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LM3463 EN and DIMn pin questions

Kazuya Nakai59
Guru 20805 points
Other Parts Discussed in Thread: LM3463, SN74LVC1G07, SN74AUP1G17

 Hello guys,

 Our customer has the following questions about LM3463. I checked LM3463 datasheet but I couldn't find the answers. If these questions are solved, they will start to evaluate this device.

 1. What voltage is the internal pull-up of EN pin connected to? Is it VCC voltage?

If so, I think EN pin is charged up to  6.76V. Is my understanding correct?

 2. What is the pull-up resistance of the EN pin?

 3. Is there any block diagram or equivalent circuit of EN pin portion?

 4. Is there any open drain CMOS logic IC which can drive the EN pin directly?

     I checked SN74LVC1G07 (Single Buffer/Driver With Open-Drain Output) datasheet

and I found the recommended maximum voltage of open drain output is 5.5V.

So the logic device can 't be used for EN pin driving. 

 5. Is there any CMOS buffer logic IC which can drive the DIM01/DIM23 pin directly?

    I checked SN74AUP1G17(LOW-POWER SINGLE SCHMITT-TRIGGER BUFFER) datasheet

and I think the logic IC can drive DM01/DM23 directly at 3.3V because LM3463 DM01/DM23 pin

input high level voltage threshold is 1.75V as the maximum.

 6. Is the power supply of the DIM01/DIM23 input buffer VCC?

 7. If the answer for No.6 question is yes, I think a few current leaking from VCC at DIM01DIM23

input buffer when 3.3V is applied to DIM01/23 because the input voltage is not VCC and is not full

swing. Then is VIN shut down current increased?

 8. Is there any block diagram or equivalent circuit of DM01/DIM23 pin portion?

 Your reply would be appreciated,

Best regards,

Kazuya Nakai.

  • 0
    Guru 20805 points
    Hi guys,

    Our customer wants to use LM3463 if the questions are cleared.

    Could you please give me your answers ASAP?

    Thank you and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Expert 3910 points

    Hi Nakai-san,

    I am sorry that your questions are not answered promptly.

    1. EN pull-up: it’s an internal current source (small current at range of uA) pull-up to a voltage higher than VCC, yet, the pin has been clamped at around 5V internally;

    2. EN pull-up resistance: it’s a current source pull-up so the impedance is high, however, we did not measure such impedance so we don’t have data;

    3. EN pin simple block diagram:

    4. We suggest EN pin being driven by an external MOSFET for pull-down shut-off. If external driven is necessary, please make sure the driving voltage is below 5V (absolutely below 5.5V at all conditions).

    5. As long as a driver that has higher than 1.75V (max) for “1” and lower than 1.1 V (min) for “0”, this driver can be used to drive DIM01/DIM23 signals.

    6. The signals DIM01/DIM23 are connected into a hysteresis comparator. The comparators are driven by internal digital rail voltage, not VCC.

    7. There should have no current flowing from either VCC or internal digital voltage as the signals are connected to the high-impedance input of the comparators.

    8. DIM01/DIM23 simple block diagram:

    I hope the above answered your questions.

    Thank you very much!

  • 0 in reply to Issac Hsu
    Guru 20805 points
    Hi Issac,
    Thank you very much for your prompt reply.
    I could understand well about LM3463 EN and DIMn pin because of your perfect answers.

    I will explain our customer about EN and DIMn pin base on your answers.

    Thank you again and best regards,
    Kazuya Nakai.