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LM3492: Interface Spec 4 MCU control signals

Siegmund Schlechter
Prodigy 20 points
Part Number: LM3492

I'd like to connect some LM3492 signals to an MCU.

The datasheet 7.1 Absolute Ratings shows Output Voltage values for COMM, DIM1, DIM2 only,

but what about Max Input voltage? Is it the same?

And what about VEN max?

There are also no input current values for COMM and IDIMn pins.

Which current can those pins drive?

Thanks a lot for your help!

Sigi

  • 0
    TI__Mastermind 20905 points

    Hello Siegmund,

    I am sorry the "EN" pin wasn't called out on the abs max table.  I would be conservative and assume that it is like COM, DIM1, etc and their abs max is 6V. 

    The max input voltage is labeled, so I am a bit confused about what you wrote previously.  

    The DIM pins are inputs so they are high input impedance.  The input currents will be very small.  

    COM is an open drain pin, The max resistance of the internal N-FET is 0.7V (VCOLL-LOW) divided by 5mA, which is 140 ohms max.  The pullup resistor on that line will set the max current.  Worst case would be abs max voltage 6V divided by 140 ohms, which is ~43mA.  

  • 0 in reply to fhoude
    TI__Mastermind 20905 points

    Can you elaborate on what hasn't been resolved?

  • 0 in reply to fhoude
    Prodigy 20 points

    It's my bad being not clear enough.

    So, what is the max INPUT VOLTAGE for EN, COMM, DIMn?
    VDIM-HIGH is labeled as 1.17V Min, but Max is missing. 

    The specification is a min of the logic high for that function.  The max is just the max operating or abs max of the pin.  This is the same for COMM, and DIMx pins, where the abs max is 6V.  This is in the datasheet.  

    VEN rising shows 1,71V max, but IEN-OPER shows 2V for test condition, I assume applying less than 5.5V would be fine? Yes, that is above VEN rising.

    The Electrical Characteristics do not show any input voltage value for COMM. This is a open drain signal.  The high voltage is set by the pullup resistor and to what supply that is connected to.  You need to make sure that is less than abs max of 6V.  We have it connected to our Vcc in our datasheet.

    Since EN, COMM, DIMn could be used for MCU control, I assume applying 3.3V or even 5V will be fine? Yes, that should be fine.

    Best regards!

    Sigi