Part Number: LM339B
Other Parts Discussed in Thread: LM339
Hi Amplifiers team, I have an engineer asking about the current limit of the LM339BIPWR hwne the voltage at the IN- pin is greatere tan the V+ pin (V- = GND)?
The existing design uses 150k current limiter resistor (-V).
The datasheet shows -50mA Max.
Thanks.
Hello Vincent,
The -50mA is the limit for the body diode if the output is pulled below ground.
When the -IN is greater than +IN, the output is low and is "sinking" current (output connected to GND pin).
The "output sink current" 25mA line is the abs max current for the output sinking.
However, the output will limit the current at about 18-20mA, so you should not see 25mA.
The output is mostly resistive, and the actual output voltage will depend on how much current is sunk.
Everything you need to know is in the "Output Low Voltage vs. Output Sinking Current" graphs Figs 6-19 thru 6-22.
This is the voltage on the output when "low" (sinking). The more current, the higher the voltage (VOL).
The sharp inflection after 10mA is the current limit. The current limit is generally in the 16-18mA range.
For example, if you were sinking 1mA (5k pull-up resistor at 5V), then the output would be about 40mV.
At 150k, even at 36V, that would be 240uA, which from the graph would be about 15mV.
For more information on the output, please see section 7 of the LM339 family application note:
Application Design Guidelines for LM339, LM393, TL331 Family Comparators
