LM1117: Question about Peak Current of LM1117

Dear Sukmin,

Thanks a lot for reaching out on e2e about TI's LDOs. 

LM1117 is rated to provide 800mA of load current. So it should be used for max 800mA current system only.

The current limit is a basically an over current protection mechanism internal to the LDO.

There are external fault conditions and scenarios where an LDO might experience an unexpected high current draw. During these events, LDO will internally limit the current flowing through it. This over current protection limit is defined in EC table with-in the range of 800mA - 1500mA. Once the fault is cleared, LDO will return back to regulating the output node. 

In the current limit operation, LDO will not be able to meet Electrical specifications related to the output voltage (such as output accuracy, line regulation, load regulation etc.)/

Apart from the this, overall power dissipated across the LDO will also define the maximum load current supported. 

For e.g. in your case, as VIN-VOUT headroom is 6V. Supporting 0.8A of load current, the overall power dissipation across LDO would be 4.8W.

Depending upon the package used and its thermal performance parameters, the max power dissipated is limited as shown in Table 7.1 of the datasheet.

PD = (TJ(max)–TA)/RθJA

For e.g. as shown in Table 5 of the datasheet, for TO-220 package RθJA is 23.8 C/W. 

So for TA = 25C, max power supported would be PD = (150-25)/23.8 = 5.25W. Which is less than your power requirement.

Here is the snapshot of Table 5

You can read more in details about the same on the app note about LDO basics (specifically Chapter 3 & chapter 5). 

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To drive a motor control with peak current of 1.5A, I would request you to go for LM317 family of device.

Please let me know in case further details are needed.

Regards,
Rohit Phogat