LP2951-N_15_15 Datasheet, PDF (26/50 Pages) Texas Instruments – LP295x-N Series of Adjustable Micropower Voltage Regulators

LP2950-N, LP2951-N
SNVS764O – JANUARY 2000 – REVISED DECEMBER 2014
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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: V_OUT of regulator 1 is programmed one diode drop above 5 V. Its error flag becomes active when
V_IN ≤ 5.7 V. When V_IN drops below 5.3 V, the error flag of regulator 2 becomes active and via Q1 latches the
main output off. When V_IN 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 V_OUT option, the error flag pin keep output high, which will turn off PNP bipolar
and pull SD pin to low, then the LP2951 keeps output regulated voltage.
When output drop to less than 95% of V_OUT option, it will trigger error flag output a low voltage, which will turn on
PNP bipolar and pull SD pin to high, then chip enter shutdown mode and turn off output voltage. During
shutdown sequence, error pin will continue output low and the LP2951 latched in shutdown mode.
Figure 49. Latch Off When Error Flag Occurs
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