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LMH6703: disable function - operation with assymetrical split supply

pinhas rosenfelder
Prodigy 50 points

Part Number: LMH6703

Tool/software:

I have an LMH6703 working from +9V and neg3V split supplies.  in the data sheet there is a phrase about "For 5-V supplies only, the LMH6703 has a TTL logic compatible disable function"

does that mean the disable function cannot operate in my configuration?  or it just means that different voltage levels are required to disable?

there is also reference to low being <0.8V, and also "to prevent the shutdown pin voltage from going more than 0.8 V below the midpoint of the supply voltages.

SO I understand in my case- where midpoint is +3V, I would need a voltage between 2.2V and 3.8V to disable?

and a voltage above +5V as a logic high - to what maximum?  and would 4.9V work?

ALSO - WHEN DISABLED - WILL THE OUTPUT GO LOW RAIL?  TO MIDPOINT?  OR?

also - I see a typ 10ns time for enable and disable - is there a maximum time?

thanks

Pinhas

  • 0
    TI__Mastermind 20470 points

    HI Pinhas,

    This is a typo, I do not see why this function would not work in your supply configuration. The wording is a little confusing, but you are correct. At a mid-supply of 3V, that sentence states that 0.8V below mid-supply could result in damage. So, setting a voltage of 2.2V or below could damage the device. 0.8V from mid-supply so 3.8V should disable and 2V above mid-supply should enable the device. As long as you don't go below 2.2V, you should be ok. For the max voltage, this isn't specified but we highlight 3V above mid-supply in our datasheet so I would say to stay below 2V from the rail. We state 2V above mid-supply (3V in this case) so I would not be certain 4.9V would work. As it is shutdown, the output stage will be high impedance, and I believe the output voltage would just get pulled to whatever voltage your load is biased to. As for the maximum time, as this is an AC spec, we don't test these parameters at final test which means we do not guarantee a maximum value. Specs in the EC table with a maximum indicates it's a tested specification and we can guarantee its max value.  

    Best Regards,

    Ignacio