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LMV331: Vout and sink current

na na78
Guru 16770 points
Part Number: LMV331


Hi

I don't get the relationship between Io(sinking) and Figure 3.

1.

At VCC=5V Ta=25C, figure 3 shows 45mA sink current when Vout=550mV.

Does it mean RCE is ~12.2ohm?

2.

Could you explain about Io (output current sinking) from electrical char at VCC=5V?

According to datasheet, Io is 10mA(min), 84mA(typ) when Vo<=1.5V.

Does it mean we have to select Rpullup to keep sink current at least 10mA when output is low?

BestRegards

  • 0
    TI__Guru 63416 points
    Hello Na Na,

    #1: Yes. 550mV/45mA=12.3 ohms equivalent. You could model the output sinking as resistive as long as you are in the linear portion of the curve.

    #2 There is no "required" pull-up current value.

    Higher value pull-up resistors use less current and allow the output to swing closer to GND, but at the expense of output rise time.

    Lower value resistors draw more current when low, but improve the output rise-time at the expense of minimum negative output swing.

    We recommend a pullup current between 100uA to 1mA for best power/speed trade off.

    The 1.5V output value comes from the production test that is testing the output current limit. 1.5V is really an impractical output low value for most applications. It is saying that it is typically 84mA when Vout is 1.5V, but is guaranteed to be at least 10mA .
  • 0 in reply to Paul Grohe
    Guru 16770 points
    Hi Paul

    Thank you for your information!

    Bestregards
  • 0 in reply to Paul Grohe
    Prodigy 10 points

    Hello,

    The datasheet (Section 6.7) shows the Output Sink Current is 10mA in the MAX column, not MIN.

    Is the "10" in the wrong column?

  • 0 in reply to gene daunis
    TI__Guru 63416 points
    Hello Gene,

    It's a little confusing... The spec says that the output low (VOL) will be <=1.5V at a maximum sink current of 10mA. The "min" is actually in the condition.

    In other words: At a maximum of 10mA sinking, the output will be less than 1.5V. Not really a realistic spec for customer use, but that is how we test for maximum current in production test.

    So if you look at the figure 3 graph "Output Voltage vs. Output Current at 5-V Supply" - there is obviously a lot of room in this spec. Typically the output voltage is about 250mV at 10mA.