LM293: Short-circuit breakdown between PIN-8(VCC) and PIN-4(GND)

Hello Dice-K,

The LMx39 family is built on an older high voltage junction-isolated process. This means there is essentially a reversed-diode to the GND pin under every internal circuit node. If the supply voltage is reversed, these diodes start to conduct and currents start flowing where they should not.

The LMx39 family is older and does not have the supply clamping circuits that "modern" devices have. So there is no defined path that the reverse current will flow through, so damage can occur if the reverse currents are unlimited.

Across the supply pins, the device will look like a soft, leaky diode when the supplies are reversed. Like a PN diode, currents will start flowing at -450mV and can rise to several hundred mA when over -800mV. There is no current limiting - until something finally "blows" and damage occurs. There is no specification for this condition.

Similarly for a "latch" condition, where a supply "glitch" causes an SCR type latch-up across the supplies (or inputs), the latch current is also not limited and can also reach several hundred mA (depending on where in the circuit the "latch" occurred). This condition usually results in destruction if there is enough current available in the supplies.

For "normal" supply operation, the output current is limited to about 16mA should the output get shorted to V+ (up to 30V). At that point, the thermal dissipation (heating) can cause damage.