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tlc551: CONT pin; 1V operation of part

Pongo
Intellectual 270 points
Part Number: TLC551
Other Parts Discussed in Thread: TLV1702

Hello,

Does the part tlc551 truly function down to 1V or am I missing something? For example, do the propagation delays from input to output become really slow?

Also, I'm trying to find out more about the CONT pin on part tlc551. The datasheet says that the CONT provides direct access to the 2/3 point on the voltage divider, and that BOTH the threshold voltage AND the trigger voltage are adjustable from the control pin. So the questions are:

1.) How close to Vdd can the CONT pin be(but still less than Vdd) while still maintaining functionality of the THRESH and TRIG pins? Likewise, how close to GND can the CONT pin be? Are we talking 50mV or so here?

2.) Relating to question 2: I'm assuming that more overdrive on the comparators implies faster overall switching. So then, would the comparator become very slow if CONT was brought close to either Vdd or GND?

3.) If, hypothetically, the CONT were tied to Vdd, then would the threshold value then become 1/2 Vdd since this would effectively short out the top resistor?

Thanks

  • 0
    TI__Genius 15410 points

    Hello Pongo,

    Yes the device functions down to 1V. The minimum supply voltage stated in the datasheet is 1V.

    As the supply voltage decreases the propogation delay and the Discharge switch on-state resistance increases. Please see figures 1 and 2 in the datasheet for more information.

    1. If a voltage is applied to CONT pin it is recommended to use a voltage between 10% and 80% of the supply voltage. Please see the last sentence in the application section of the datasheet.

    The maximum voltage that can be applied to the CONT pin is VDD. However, applying VDD to the CONT pin for extended periods may effect device reliability. Please see the absolute maximum rating in the datasheet.

    2. More overdrive on the comparator does not necessarily mean faster overall switching. Take for example the TLV1702, in general the more overdrive voltage the slower the propogation delay. But as you can see in the TLV1702 datasheet (figure 8) the curve is not linear so I cannot say for sure how the TLC551 will perform with different overdrive voltages. Additionally this information is not provided in the TLC551 datasheet.

    3. If CONT is tied to VDD the threshold (THRES) must be greater than CONT (VDD) for the comparitor to go high. The TRIG voltage would become 1/2 VDD if CONT is tied to VDD. I do not recommend using the device in this configuration.

    Thank you,

    Tim Claycomb