# Estimate the necessary input if desired output voltage

#### Kelvin Lee

Joined Oct 22, 2018
111

Not sure whether here is the correct forum I should post my question here.

Refer to datasheet https://nvhs.files.wordpress.com/2013/02/datasheet-l9110.pdf

From the above test table, the input voltage is 9V but the output is 7.5 ~ 7.7V, may I assume there is about 1.3 ~ 1.5V is being consumed by the module L9110? If I expect the final output is 3V, then should I provide the input voltage at around the range 4.3 ~ 4.5V? Is it the same if my desired output is at 5V and I simply add 1.5V more as the input voltage? If not, how do I estimate the input voltage I should provide?

Best regards,

Kelvin.

#### Papabravo

Joined Feb 24, 2006
17,614
That's a real fine A#1 datasheet you got there -- real informative.

You should not assume anything. The chip is a motor controller. Just because the outputs do not go all the way to the power supply rails you CANNOT assume that power is being consumed. It may be but it is not a requirement. The only way to know is to build the circuit and measure power in and power out. That way you will know and you won't have to assume.

The input voltage should meet the stated specifications for logic "0" (0-0.7 VDC) and logic "1 (2.5 - 9 VDC) The inputs should neither sink, nor source very much current. Nothing produced by a random Chinese company would surprise me however.

Q: Do you know what the meaning of "road input pin" and "road output pin" might be? Wonderful translators they have.

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#### ronsimpson

Joined Oct 7, 2019
1,752
I disagree with your idea. Mr. Lee,
A input is "low" if it is anywhere from 0 to 0.7. It will not effect the output if the input is changed from 0.1 to 0.6. (no change)
The same applies for "high".
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The output voltage pulls up or down depending on if the input is low or high.
If the output is low (or high), the voltage is more a function of output current. If there is no motor the voltage will be very low or very high. The voltages in the data sheet is with a motor (or load) of 750mA.