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LM1117IMP-3.3/NOPB LDO Reverse current Protection

Sugumar Krishnasamy
Intellectual 420 points
Other Parts Discussed in Thread: LM1117, SM74611

We are using LDO: LM1117IMP-3.3/NOPB (SOT-223 package) for +5V input to +3.3V output voltage.

We have also has the +3.3V battery backup at the output of LDO (LDO output pin and battery +ve pins are shorted).

Whenever Input signal is not available to LDO, the batter will supply power to our circuit.

Now our question is, Whether the LDO can withstand a battery voltage at LDO output pin while the LDO input is left open circuit.


I have seen the datasheet of Linear Technology LDO: LT1764 datasheet at page No: 14, They have clearly mentioned in 7th paragraph and given the LDO sink current in Figure 5. The LT1764-3.3 can sink 0.7mA reverse O/P current at battery O/P voltage at +3.3V.


But we are unable to find these Reverse current Protection of above LDO in the datasheet.

So kindly conform the Reverse current protection capability of  LDO : LM1117IMP-3.3/NOPB


Regards,

Sugumar K

India

  • 0
    TI__Expert 3920 points

    Hi,

    Please see Protection Diodes section of the datasheet. It explains how much reverse current the internal diode can handle inside the LM1117.

    If the input is truly open, then I do not see any issues since no current will be flowing from output to input. If you have an input capacitor, then a quick transient at the output can cause a reverse surge current which may potentially damage the internal diode if large enough. You may place a protection doide between the output and input pins to divert current from the internal diode in case this happens.

    Have you also taken a look at ORing the two supplies? SM74611 might be a good fit here, acting as a very low drop diode (~26mV).

    Tim