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AD680AN bảng dữ liệu(PDF) 7 Page - Analog Devices |
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AD680AN bảng dữ liệu(HTML) 7 Page - Analog Devices |
7 / 8 page AD680 REV. C –7– One such ADC that the AD680 is well suitcd for is the AD7701. Figure 12a shows the AD680 used as the reference for this converter. The AD7701 is a 16-bit A/D converter with on-chip digital filtering intended for the measurement of wide dynamic range, low frequency signals such as those representing chemical, physical or biological processes. It contains a charge balancing (sigma-delta) ADC, calibration microcontroller with on-chip static RAM, a clock oscillator and a serial communica- tlons port. This entire circuit runs on ±5 V supplies. The power dissipation of the AD7701 is typically 25 mW and, when combined with the power dissipation of the AD680 (1 mW), the entire circuit consumes just 26 mW of power. AD7701 MODE SDATA SC1 DGND CLKOUT CLKIN AGND SCLK SC2 CAL CS BP/UP DV SS AV SS A IN V REF AV DD DV DD SLEEP RANGE SELECT CALIBRATE ANALOG INPUT ANALOG GROUND –5V ANALOG SUPPLY 0.1 µF SERIAL DATA SERIAL CLOCK READ (TRANSMIT) DATA READY 0.1 µF 0.1 µF 0.1 µF 10 µF DRDY AD680 V IN V OUT GND +5V ANALOG SUPPLY 0.1 µF10µF 0.1 µF Figure 12a. Low Power, Low Voltage Supply Reference for the AD7701 16-Bit A/D Converter Figure 12b shows the AD680 connected to the AD773 high speed 8-bit ADC. The low pass filter shown minimizes the AD680’s wideband noise. AD680 2 GND V IN V OUT 4 6 REF IN REF GND 22 Ω 10µF 0.1µF AD773 2 1 Figure 12b. AD680 to AD773 Connection The AD773’s high impedance reference input allows direct con- nection to the AD680. Unlike the resistor ladder requirements of a flash converter the AD773’s single pin, high impedance in- put can be driven from one low cost, low power reference. The high impedance input allows multiple AD773’s to be driven from one AD680 thus minimizing drift errors. +4.5 V REFERENCE FROM A +5 V SUPPLY The AD680 can be used to provide a low power, +4.5 V refer- ence as shown in Figure 13. In addition to the AD680, the cir- cuit uses a low power op amp and a transistor in a feedback configuration that provides a regulated +4.5 V output for a power supply voltage as low as +4.7 V. The high quality tanta- lum 10 µF capacitor (C1) in parallel with the ceramic 0.1 µF capacitor (C2) and the 3.9 Ω resistor (R5) ensure a low output impedance up to around 50 MHz. 3 2 4 6 7 +IN –IN V+ V– OUT OP-90 CF 0.1µF R4 3.57k R5 3.9 C2 0.1µF +C1 10µF R1 2k 1% R2 2.5k 1% CC 3.3µF R3 1k 2N2907A +4.7V TO +15V AD680 VOUT +V IN GND +4.5V 0.1µF Figure 13. +4.5 V Reference Running from a Single +5 V Supply VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT The AD680 is ideal for providing a stable, low cost and low power reference voltage in portable equipment power supplies. Figure 14 shows how the AD680 can be used in a voltage regu- lator that not only has low output noise (as compared to a switchmode design) and low power, but also a very fast recovery after current surges. Some precaution should be taken in the selection of the output capacitors. Too high an ESR (effective series resistance) could endanger the stability of the circuit. A solid tantalum capacitor, 16 V or higher, and an aluminum elec- trolytic capacitor, 10 V or higher, are recommended for C1 and C2, respectively. Also, the path from the ground side of C1 and C2 to the ground side of R1 should be kept as short as possible. 2 3 6 7 2 3 4 4 VIN TEMP GND AD680 402k Ω 1% 402k Ω 1% OP-20 ++ 68µF TANT C1 1000µF ELECT C2 +5V, 1A IRF9530 510k Ω CHARGER INPUT + LEAD-ACID BATTERY 6V VOUT 6 0.1µF R1 R2 R3 Figure 14. Voltage Regulator for Portable Equipment |
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Mô tả tương tự - AD680AN |
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