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TL3116: truth table

Part Number: TL3116
Other Parts Discussed in Thread: INA301, , INA293

Hello,
customer want to measure a 2A current high side at 110V. He is looking for the INA293 but needs an alert/latch pin like in the INA301. Therefor wants to use the TL3116 which has an latch output. The TL3116 is very limited. Can you share a truth table to understand the exact working of this IC. Is there any any application note?
Also please let me know if you have other current shunt recommendation.

Regards, Holger

  • Holger

    I see what you mean about the TL3116 having limited information in the datasheet.  Unfortunately this is a very old part that does not have any supporting documents to accommodate the datasheet. 

    The input to the comparator is relatively standard.  If IN+ > IN- (excluding input offset voltage), then Q_OUT is logic high and QB_OUT is logic low.  The output logic levels for Q_OUT and QB_OUT are relative to the ground pin (GND) and limits for VOH and VOL are specified in the EC table on page 4 of the datasheet.

    The LATCH_ENABLE pin will latch or hold the comparator outputs in their current state when in a logic high state.  Once the LATCH_ENABLE is asserted, the output of the comparator will no longer track changes on the inputs to the comparator.

    Please help me understand what you are trying to accomplish with the INA and the comparator.  Do you want to use the LATCH_ENABLE pin as a means to sample the output of the comparator at a given time (hold the outputs at their present state), or do you want to use the LATCH feature in such a way that the output of the comparator will remain high whenever an over-current condition occurs. Unfortunately, the TL3116 does not function in this manner.

    If you are looking for a solution where the output of the comparator will self-latch (transition from low to high and remain in that state) whenever an over-current event occurs, I recently released an app note where I use a comparator with a current sense amplifier to accomplish this.  See www.ti.com/.../snoaa21.pdf.  In this circuit, the output of the comparator controls the REF pin of the INA.  If an over-current condition occurs, the comparator output goes high which levels shifts the output of the INA up.  Since the output of the INA was already higher than the reference of the comparator, the over current condition will remain with the comparator output latched at a logic high level.  The only way the latched condition can be cleared is by power cycling the power to the circuit.  The same result could be accomplished with the INA293 if the comparator output controlled the GND pin.

    Chuck

  • Hello Chuck,
    thanks for the details answer.
    Yes, the want to latch the output in case of an overcurrent and read/poll it back later.

    Can you also feedback the output of the TL3116 to the enable pin to latch the overcurrent?

    Regards, Holger

  • Holger

    That is a clever idea.  You could use the output of TL3116 to control the latch enable pin.  The only potential issue with that is that the latch enable pin has some setup time requirements.  You may need to put a small RC filter between the output pin and the latch enable pin to make sure the output is stable for around 10ns before activating the latch enable.  I would at least design with an RC filter on the output of the comparator and if it is not needed the capacitor could be left open and the resistor could be stuffed with 0 ohms.  You just need to make sure that you latch the output condition that you desire.  If the input changes faster than the propagation delay or faster than the latch feature can be enabled, you could latch a non-overcurrent condition but that seems very unlikely.  You could also put a little filter on the input to the comparator to make sure that input glitches do not activate your circuit.  That would probably solve this issue since the input would not change so rapidly.

    Chuck