Datasheet LTC1540 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | Nanopower Comparator with Reference |
| Páginas / Página | 14 / 9 — TYPICAL APPLICATIONS 3.3V Output Low Dropout Linear Regulator. Auto … |
| Formato / tamaño de archivo | PDF / 209 Kb |
| Idioma del documento | Inglés |
TYPICAL APPLICATIONS 3.3V Output Low Dropout Linear Regulator. Auto Power-Off Source
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LTC1540
TYPICAL APPLICATIONS 3.3V Output Low Dropout Linear Regulator
is the switched power supply output. With a 10mA load, it The LTC1540 can be connected as a micropower (I typically provides a voltage of (VBAT – 0.17V). The whole Q = 5.5µA at V circuit draws a mere 0.8µA of quiescent current with VBAT IN = 5V) low dropout linear regulator (Figure 7). When the output is low, Q1 turns on, allowing current to = 5V. The three resistor voltage divider programs 50mV of charge output capacitor C1. Local feedback formed by hysteresis for the comparator, and sets the IN– voltage at R4, Q1 and Q2 creates a constant-current source from the 200mV. This gives an IN+ trip threshold of approximately 5V input to C1. R4, R1 and Q2’s V 150mV BE also provide current limiting in the case of an output short-circuit to ground. C2 The RC time constant determines the maximum power-on reduces output ripple, while the R2-R3 feedback voltage time of the OUT pin before power down occurs. This period divider establishes the output voltage. can be approximated by:
Auto Power-Off Source
t = 4.6RC (seconds) Figure 8 shows the circuit for a 30mA power supply that The actual time will vary with both the leakage current of has a timed auto power-off function. The comparator output the capacitor and the input current at the IN+ pin. V V BAT IN = 5V R4 10Ω 7 MOMENTARY 7 Q2 2N3906 V+ SWITCH LTC1540 V+ Q1 LTC1540 IN+ 3 3 IN+ TP0610L R1 + C R OUT 8 47k VOUT 4 IN– 3.3V + – C1 10µF OUT 8 (V 432k BAT – 0.17V) 10mA 4 IN– 5 HYST – R3 C2 2M 750k 2.2nF 5 HYST 6 REF 1% 121k C3 R2 430k 6 REF GND V– 1% 1 2 V– GND 2 1 1540 F07
Figure 7. 3.3V Output Low Dropout Linear Regulator
1540 F08
Figure 8. Auto Power-Off Switch Operates on 0.8µA Quiescent Current
1540fb For more information www.linear.com/LTC1540 9
TYPICAL APPLICATIONS 3.3V Output Low Dropout Linear Regulator
is the switched power supply output. With a 10mA load, it The LTC1540 can be connected as a micropower (I typically provides a voltage of (VBAT – 0.17V). The whole Q = 5.5µA at V circuit draws a mere 0.8µA of quiescent current with VBAT IN = 5V) low dropout linear regulator (Figure 7). When the output is low, Q1 turns on, allowing current to = 5V. The three resistor voltage divider programs 50mV of charge output capacitor C1. Local feedback formed by hysteresis for the comparator, and sets the IN– voltage at R4, Q1 and Q2 creates a constant-current source from the 200mV. This gives an IN+ trip threshold of approximately 5V input to C1. R4, R1 and Q2’s V 150mV BE also provide current limiting in the case of an output short-circuit to ground. C2 The RC time constant determines the maximum power-on reduces output ripple, while the R2-R3 feedback voltage time of the OUT pin before power down occurs. This period divider establishes the output voltage. can be approximated by:
Auto Power-Off Source
t = 4.6RC (seconds) Figure 8 shows the circuit for a 30mA power supply that The actual time will vary with both the leakage current of has a timed auto power-off function. The comparator output the capacitor and the input current at the IN+ pin. V V BAT IN = 5V R4 10Ω 7 MOMENTARY 7 Q2 2N3906 V+ SWITCH LTC1540 V+ Q1 LTC1540 IN+ 3 3 IN+ TP0610L R1 + C R OUT 8 47k VOUT 4 IN– 3.3V + – C1 10µF OUT 8 (V 432k BAT – 0.17V) 10mA 4 IN– 5 HYST – R3 C2 2M 750k 2.2nF 5 HYST 6 REF 1% 121k C3 R2 430k 6 REF GND V– 1% 1 2 V– GND 2 1 1540 F07
Figure 7. 3.3V Output Low Dropout Linear Regulator
1540 F08
Figure 8. Auto Power-Off Switch Operates on 0.8µA Quiescent Current
1540fb For more information www.linear.com/LTC1540 9