• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 606 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

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.

LMC6772: What can this device sink?

David Cano
Prodigy 50 points
Part Number: LMC6772

The specs for the LMC6772 under "Absolute Maximum Ratings" mentions "Current at Output Pin ±30 mA"  . Does this mean that this is the maximum current sinking ability? Also, why "+/-" ? The device can only sink current, not supply.

Also, under "Short Circuit Sinking" graph shows about 35mA at 12V.  Short what?  If (on state) I were to short the drain to 12V I would expect the drain current to go much higher than 35mA, and the device would probably not survive very long.

It's all a little confusing. Please explain.

Thank you.

  • 0
    TI__Mastermind 49906 points
    Hi David,

    The ±30mA is really the current limit for the ESD clamp diodes, which can be either polarity, hence the "±". Same for the 5mA current on the input pin.

    Notes 4 and 5 state:

    "(4) Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150°C. Output currents in excess of ±30 mA over long term may adversely affect reliability."

    "(5) Do not short circuit output to V+, when V+ is > 12V or reliability will be adversely affected."

    Figure 12 also shows the short circuit action over temperature - and, yes, the current can go over 30mA. It was found that the output stage could break down at high voltages (>12V) when shorted - and the subsequent addition of the notes.

    So what you have proposed violates both of the notes...so don't do that!!!

    The LMC6772 is a micropower device and is not designed for high currents (<10mA). The load current should be limited if the supply voltage is >12V (usually with a resistor).
  • 0 in reply to Paul Grohe
    Prodigy 50 points
    Paul,
    Ohhh. … clamp diodes... got it. Thank you for such a quick reply. I still don’t see what the max drain current is. Does it say 10mA somewhere? And yes, the load will be limited by a resistor.

    Dave
  • 0 in reply to David Cano
    TI__Mastermind 49906 points
    HI Dave,

    The maximum sink current spec would be the minimum short circuit current, since during a short the output stage goes into current limit (goes constant current).

    The LMC6772 does not have a minimum short circuit specification (45mA typ - which agrees with fig 13). So it is possible it can sink over 45mA...or less...

    At that point, power dissipation and junction temperature becomes the limiting factor.

    The production test limits are at 5mA, and it does not look like a production test is done for short circuit current. For non-trimmed and/or untested parameters, you should allow for a ±30% variation across lots.

    BTW: Noticed this blurb in the Apps section:

    "OUTPUT SHORT CIRCUIT CURRENT

    The LMC6772 has short circuit protection of 40 mA. However, it is not designed to withstand continuous short
    circuits, transient voltage or current spikes, or shorts to any voltage beyond the supplies. A resistor is series with
    the output should reduce the effect of shorts. For outputs which send signals off PC boards additional protection
    devices, such as diodes to the supply rails, and varistors may be used."

    So gain..don't do that! And limit the current to <10mA.