If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

# TLV3401: Pull up resistor

Part Number: TLV3401
Other Parts Discussed in Thread: TLV7031, , TLV7041

Hi Team,

The recommended pull up resistor is 1MΩ, we want the circuit to have higher output current, so the pull up resistor is changed to 10kΩ, but the simulated result shows that the output low voltage can only reach 0.58V rather than 0V.

The TINA shows there is sink current in the output, could you please help tell why the output voltage cannot reach 0V and explain the output sink current? Thanks!

Best Regards!

Hao

• Hao,

As you sink more and more current using a smaller resistor pullup, the voltage across the Rdson of the comparator increases and raises the ground floor of the device output.

Generally with low power parts, you want to use a large pullup resistor to avoid this case. While a smaller pull up resistor will give you faster speeds, the amount of power a 10k pullup burns will be much more significant than a 1M resistor and will also raise your ground floor.

Have you tried simulating your circuit with pullup resistors in the range of 100kohms? Do you have a required speed you would like to achieve from the output?

Regards,

Jonny

• Hi Jonny,

100kohms resistor is much better and the voltage goes almost to 0V.

The internal mosfet seems to have very large Rdson, it can be calculated from the TINA simulation the Rson is (581.44mV/271.86uA=)2.1kΩ. May I may why Rdson is so large? Because the most of the mosfet has less than 10Ω Rdson.

Thanks and Best Regards!

Hao

• Hao,

The Rdson is large because it was the way the part was designed to work. For these older comparator parts that are nanopowered, you can see in the datasheet curves that the Vol levels can be quite high when you are sourcing as much current as you want using a 10k resistor.

I noticed that your supply and pullup are the same value. Is there a reason why you are using an open drain part? You could use a push-pull output comparator that could drive higher speeds and not have the issue of raising the ground floor too high.

I would suggest taking a look at the TLV7031. It is our low voltage, nanopower push pull comparator available in leaded and space saving leadless options. If you were to use the open drain version of the part (TLV7041) and you wanted to source 0.33mA of current, your ground floor will be only 40mV at a 1.8V supply for example. This gives already a 10x improvement in comparison to the TLV3401.

Regards,

Jonny

• Hi Jonny,

Thanks for the detailed explanation. 100kohms resistor meet our requirements. We will consider using push-pull output comparator if more current is needed.

Best Regards!

Hao