1540 查看數據表（PDF） - Linear Technology

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1540

Nanopower Comparator with Reference

Linear Technology 

LTC1540

TYPICAL APPLICATIONS

3.3V Output Low Dropout Linear Regulator

The LTC1540 can be connected as a micropower (IQ =

5.5µA at VIN = 5V) low dropout linear regulator (Figure 7).

When the output is low, Q1 turns on, allowing current to

charge output capacitor C1. Local feedback formed by R4,

Q1 and Q2 creates a constant-current source from the 5V

input to C1. R4, R1 and Q2’s VBE also provide current

limiting in the case of an output short-circuit to ground. C2

reduces output ripple, while the R2-R3 feedback voltage

divider establishes the output voltage.

Auto Power-Off Source

Figure 8 shows the circuit for a 30mA power supply that

has a timed auto power-off function. The comparator

output is the switched power supply output. With a 10mA

load, it typically provides a voltage of (VBAT – 0.17V). The

whole circuit draws a mere 0.8µA of quiescent current with

VBAT = 5V. The three resistor voltage divider programs

50mV of hysteresis for the comparator, and sets the IN –

voltage at 200mV. This gives an IN + trip threshold of

approximately 150mV

The RC time constant determines the maximum power-on

time of the OUT pin before power down occurs. This period

can be approximated by:

t = 4.6RC (seconds)

The actual time will vary with both the leakage current of

the capacitor and the input current at the IN + pin.

VIN = 5V

3 IN+

4 IN–

7

V + LTC1540

Q2

2N3906

+

R1

OUT 8

47k

–

R4

10Ω

Q1

TP0610L

VOUT

C1 3.3V

10µF

5 HYST

6 REF

C3

GND

V–

1

2

R3

750k

1%

R2

430k

1%

C2

2.2nF

1540 F07

Figure 7. 3.3V Output Low Dropout Linear Regulator

VBAT

7

LTC1540 V +

IN+ 3

+

432k

4

IN –

–

2M

5 HYST

121k

6 REF

OUT 8

MOMENTARY

SWITCH

CR

(VBAT – 0.17V)

10mA

V–

GND

2

1

1540 F08

Figure 8. Auto Power-Off Switch Operates

on 0.8µA Quiescent Current

8

sn1540 1540fas

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