Question about LT1464

Question

Hi All, 
 
 The Output Short-Circuit Duration spec of the LT1464 is indefinite. Does it mean that a resistor for the short-circuit proctection is not need? 
 If it's better to put such a protection resistor, I need the maximum short current value to calculate the resistor value. 
 
 Regards, 
 Kazu

GlenBrisebois · Accepted Answer

Yet the word used in the associated note I cited is "indefinitely", which does connote an unlimited amount of time.

GlenBrisebois · Answer

Hi Kazu: 
 In newer data sheets, the "indefinite" usually comes with a note: " A heat sink may be required to keep the junction temperature below the absolute maximum rating when the output is shorted indefiitely. " So basically, indefinite means that there are adequate current limits in place such that the part will not be damaged provided that the Tj is kept below the abs max, which for the LT1464 is 150C. 
 If you consult the simplified schematic, you will see that Q20 and Q21 sense the output current through R18 and R19 (which should have a ‘dot’ to the output). I checked the values, and R18/19 are nominally 20 Ohms each, which means the output current will clamp to approximately Vbe/20, which is 30mA at 25C and a -0.1mA/C tempco. 
 We don't guaranteed the max output current limit, though. And on the LT1464, the minimum output current capability is guaranteed by the Open Loop Gain and Output Voltage Swing specs with 2k load. 
 Glen Brisebois, ADI Applications