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TLV1701: Max value of pull-up resistor

Part Number: TLV1701
Other Parts Discussed in Thread: TLV3701

Hi Team, 

A customer of mine had the following question concerning the TLV1701. 

The output of the TLV1701 requires a pull-up resistor. He was wondering what the max value of the pull-up resistor might be. The application is low speed (switching 2 times every 10ms) but also very low power.

Can a pull up resistor of a few 100kohm be used?

Or is is it better to use a comparator with push-pull output in this case?

Thanks in advance for the help!

Regards, 

Obi. 

  • Hello Obi,

    The theoretical limit to the pull-up resistor is due to the output high leakage current. The typical is 70nA,  but should be below 1uA across supplies and temp. The difference between the supply voltage and the pull-up voltage will make the biggest difference in the leakage. Leakage will actually be lowest if the supply voltage is higher than the pull-up voltage.

    So at 1uA, that would be 1V across 1Meg.

    What is the supply voltage and pull-up voltage?

    If you are trying to save power, a push-pull output is preferred as you do not have a power-wasting pull-up resistor, but you loose the ability to level-shift or wire-OR the outputs.

  • Hi Paul, 

    Supply and pull-up voltage is 10V. 

    Which pull-up resistor would you recommend for lowest power loss? 

    Can you recommend a push-pull alternative (perhaps from this list)?

    Thanks. 

    Obi.

  • Hello Obinna,

    The selection of the pull-up resistor is a tradeoff between power dissipation and risetime (speed) - and also output low voltage (VOL).

    Since the output is pulled "high" by the resistor, the risetime is a function of the RC time constant of any load capacitance and the pull-up resistor value.

    If the total output trace capacitance is 100pF, a 1Mohm resistor will have a much slower risetime than a 1k resistor.

    Falltime is fixed due to the sinking output transistor, though VOL can be affected by the pull-up resistor value.

    But at 5V, the 1k resistor burns 5mA when the output is low, whereas the 1M resistor would only burn 5uA.

    Since speed does not seem to be much of an issue - and power is the critical spec, then they can probably use a pull-up resistor value in the 50k - 500k  range.

    To save more power, then a micro power push-pull output device can be used. Here the tradeoff is speed and supply current. I would recommend a device with at least 1ms response time.  Pretty much all the nanopower devcies are under 100us - so you could pretty much pick any device in the list with a P-P output, 10V supply and whatever package/channel combination is desired.

    What is their power budget? Probably the TLV3701 /2 /4 is their best bet...36us and 800nA supply current - and no pull-up!