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Original question:

TLV3604: About using negative input signal

TLV3604: Problem with wrong output and VEE

Hamid Ali
Prodigy 10 points
Part Number: TLV3604
Other Parts Discussed in Thread: TLV3601

Hello everyone!

Can I give the VEE=-2.5V and VCCi/o=2.5V for generating pulse? When i'm testing this part(with IN-=0) the VEE seemed to be clamped to around -0.6V(with a Converter generating -2.5V)

then i isolated this chip and give it -2.5V&+2.5V directly from DC power supply(still IN-=0),  the OUT+ should be -2.5V but it's around -1.2V, don't know what is the problem, could someone help to analyse?

  • 0
    TI__Mastermind 25990 points

    Hamid

    Thanks for your post and sorry for the confusion.  The logic levels of the LVDS outputs are reference to the VEE pin.  Since LVDS standard has the outputs switching around 1.2V, the output common mode is set to be 1.2V above VEE. So in the case where you make VEE = -2.5V, the outputs will be centered at -1.3V (-2.5V + 1.2V).

    Chuck

  • 0
    Prodigy 10 points

    Chuck Sins!

    Thanks for the reply, there is an other problem, i.e. when i am supplying the VEE and IN+ -2.5V with ltc1144 charge booster IC the voltage at VEE forcefully make it around -0.6V at VEE, I don't understand the reason. 

    Also, if you can provide me an alternative to tlv3604 which can work properly with the following requirements.

    i want to monitor a 20-ns repetitive negative pulse. The comparator should be fast. and convert the negative pulse to positive. 

  • 0 in reply to Hamid Ali
    TI__Mastermind 25990 points

    Hamid

    Thanks for following up.  The TLV3604 inputs are bound by VCC and VEE, so there is nothing that would clamp the input at -0.6V as long as the VEE is at -2.5V.  If you are seeing the input clamp at approximately a diode below ground, that would indicate that your VEE is actually at 0V and not at -2.5V.  The same would be true even for our TLV3601 which could also be used to invert your 20ns pulse.  Choosing between TLV3604 and TLV3601 is determined by your desired output levels.  If your downstream device is LVDS friendly, I would suggest TLV3604 but if it is single ended, I would use our TLV3601 which as a standard push-pull output stage but is still extremely fast.

    Chuck

    Example of using TLV3601.  TLV3604 would be the same on the input and power supplies.  Difference would be the 100ohm differential load between the outputs.