LP2950-N, LP2951-N
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SNVS764Q –JANUARY 2000–REVISED DECEMBER 2017
9.2.6 Regulator with Early Warning and Auxiliary Output
The LP2951 can be used to build a Regulator with early warning and auxiliary output as Figure 48 shows. it has
below features:
•
•
•
•
Early warning flag on low input voltage
Main output latches off at lower input voltages
Battery backup on auxiliary output
Operation: VOUT of regulator 1 is programmed one diode drop above 5 V. Its error flag becomes active when
VIN ≤ 5.7 V. When VIN drops below 5.3 V, the error flag of regulator 2 becomes active and via Q1 latches the
main output off. When VIN again exceeds 5.7 V regulator 1 is back in regulation and the early warning signal
rises, unlatching regulator 2 via D3.
Figure 48. Regulator With Early Warning and Auxiliary Output
9.2.7 Latch Off When Error Flag Occurs
As Figure 49 presents, a latch off when error flag occurs circuit works in below two mode:
When output is within ±95% of VOUT option, the error flag pin keep output high, which turns off PNP bipolar and
pulls SD pin to low, then the LP2951 keeps output regulated voltage.
When output drop to less than 95% of VOUT option, it triggers error flag output a low voltage, which turns on PNP
bipolar and pulls SD pin to high, then the device enters shutdown mode and turns off output voltage. During a
shutdown sequence, the ERROR pin continues output low, and the LP2951 device latches in shutdown mode.
Figure 49. Latch Off When Error Flag Occurs
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