In the literature for the LP2951M, it indicates that it has the feature of current and thermal limiting.
1 - Does this mean that if one shorts the external pins of the LP2951M to ground to simulate a short downstream of this part, it will current limit or cutout due to the thermal limiting feature?
2 - Does that also mean that if there was a short internal to the LP2951M, it would either current limit or thermally cut out? My rationale for thinking that might be the case is that the current limiting and the thermal limiting circuits would be independent of each other?
In the literature for the LM317LM, it indicates that it has the feature of current limit constant with temperature.
3 - Does this mean that if one shorts the external pins of the LM317LM to ground to simulate a short downstream of this part, it will current limit or cutout due to a thermal limiting feature?
4 - Does that also mean that if there was a short internal to the LM317LM, it would either current limit or thermally cut out? My rationale for thinking that might be the case is that the current limiting and the thermal limiting circuits would be independent of each other?
I am interested from a FMECA analysis perspective. Thank you.
Steve Radons
D. E. Hokanson, Inc.
425 882-1689
1) For the National Semi version of the LP2951, for a short circuit between the output pin and ground, the current from the output pin will be limited to 220mA maximum. The current limit threshold is determined by the saturation voltage of the internal pass transistor.
2) This specification does not apply if there is internal damage to the LP2951. For instance, if the internal pass transistor was shorted collector-to-emitter there would be no way to sense or control collector-to-emitter current. The current limit and thermal protection are two separate circuits, both of which ultimately remove the base drive from the internal pass transistor when either one, or both, is/are activated.
3) For the National Semi version of the LM317L, for a short circuit between the output pin and ground, the current from the output pin will be limited to 150mA to 300mA depending on the Vin-Vout voltage differential. The LM317 output current will run at the limit until the junction temperature approaches approximately 155C where the current will be reduced to hold the junction temperature at approximately 155C.
4) This specification does not apply if there is internal damage to the LM317L. For instance, if the internal pass transistor was shorted collector-to-emitter there would be no way to control collector-to-emitter current. The current limit and thermal protection circuits are intertwined.