Datasheet AD680 (Analog Devices) - 10

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AD680 4.5 V REFERENCE FROM A 5 V SUPPLY VOLTAGE REGULATOR FOR PORTABLE
The AD680 can be used to provide a low power, 4.5 V reference,
EQUIPMENT
as shown in Figure 19. In addition to the AD680, the circuit The AD680 is ideal for providing a stable, low cost, low power uses a low power op amp and a transistor in a feedback con- reference voltage in portable equipment power supplies. figuration that provides a regulated 4.5 V output for a power Figure 20 shows how the AD680 can be used in a voltage supply voltage as low as 4.7 V. The high quality tantalum 10 μF regulator that not only has low output noise (as compared to a capacitor (C1) in parallel with the ceramic 0.1 μF capacitor (C2) switch mode design) and low power, but it also has a very fast and the 3.9 Ω resistor (R5) ensure a low output impedance up to recovery after current surges. Some caution should be taken in approximately 50 MHz (see Figure 19). the selection of the output capacitors. Too high an ESR (effective series resistance) could endanger the stability of the circuit. A solid
4.7V TO 15V R3 CC
tantalum capacitor, 16 V or higher, and an aluminum electro-
1k
Ω
3.3
μ
F
lytic capacitor, 10 V or higher, are recommended for C1 and C2,
V 2N2907A IN +IN V+
respectively. Also, the path from the ground side of C1 and C2
V 3 7 OUT 0.1
μ
F OUT
to the ground side of R1 should be kept as short as possible.
6 AD680 OP90 –IN + C1 C2 R4 2 4 GND V– 10
μ
F 0.1
μ
F 3.57k
Ω
CHARGER CF INPUT 0.1
μ
F R5 0.1
μ
F 3.9
Ω
R3 2 510k
Ω
R2 R1 6V + V 2.5k
Ω
IN 2k
Ω
LEAD-ACID 1% V 6 – 1% 2 7 BATTERY OUT
00813-019
6 AD680 OP777 IRF9530
Figure 19. 4.5 V Reference Running from a Single 5 V Supply
TEMP 3 3 + 4 GND 4 R2 402k
Ω
1% C1 R1 + C2 + 68
μ
F 1000
μ
F 402k
Ω
1% TANT ELECT
00813-020 Figure 20. Voltage Regulator for Portable Equipment Rev. H | Page 10 of 12 Document Outline FEATURES GENERAL DESCRIPTION CONNECTION DIAGRAMS PRODUCT HIGHLIGHTS SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS OUTPUT PROTECTION ESD CAUTION PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS THEORY OF OPERATION APPLYING THE AD680 NOISE PERFORMANCE TURN-ON TIME DYNAMIC PERFORMANCE LOAD REGULATION TEMPERATURE PERFORMANCE TEMPERATURE OUTPUT PIN DIFFERENTIAL TEMPERATURE TRANSDUCER LOW POWER, LOW VOLTAGE REFERENCE FOR DATA CONVERTERS 4.5 V REFERENCE FROM A 5 V SUPPLY VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT OUTLINE DIMENSIONS ORDERING GUIDE