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LF398-N: Differential Logic Voltage

Amr Wael
Intellectual 340 points

Part Number: LF398-N

Hello,

I am planning to use LF398-N sample and hold amplifier with a microcontroller with the following logic levels.

It's written in the data sheet of LF398-N that it's differential logic threshold is 0.8 min 1.4 typical and 2.4 max

Does the threshold mean VOH differentially between pins 8 and 7 ? Will it be in this case compatible with my MCU or do I need some kind of level shifting?

Thank you very much in advance.

BR

Amr

  • 0
    Guru 322000 points

    Yes, pin 7 must be connected tio the logic ground, and pin 8 is measured relative to that.

    The input leakage current is at most 10 µA, so the actual VOH will be near VDD. I guess your VDD is above 2.4 V?

  • 0
    TI__Guru* 93105 points

    Hi Amr,

    Please refer to Clemens' response about the LF398-N logic input and reference levels.

    Regarding you question "Will it be in this case compatible with my MCU or do I need some kind of level shifting?" LF398-N datasheet Section 7, Parameter Measurement Information, provides information about the sample/hold threshold for (Section 7.1) TTL and CMOS 3 V ≤ VLOGIC (Hi State) ≤ 7 V, (Section 7.2) CMOS 7 V ≤ VLOGIC (Hi State) ≤ 15 V and (Section 7.3) Operational Amplifier Drive. It appears that Section 7.1 would be applicable to your microcontroller application. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 340 points

    in section 7.1 it's written Threshold = 1.4V 

    My Logic reference is 3.3V and pin 7 is connected to GND So does this mean that at 1.4V the signal will appear at the output and below it the signal will be held?

  • 0 in reply to Clemens Ladisch
    Intellectual 340 points

    yes the Vreference for logic is 3.3V and pin 7 is connected to ground.

    my MCU VOH is minimum 2.4V I think it's enough for driving the LF398-N to sample but my VOL max is 1.3V so if the LF398-N would sample starting form 1.4v Wouldn't that be very close to the VOL of my MCU?

  • 0 in reply to Amr Wael
    Guru 322000 points

    That VOL is measured with a load current of 20 mA. The actual load current is at most 10 µA, so the actual VOL will be at most 0.00065 V.