AD8620B(RevD) 데이터 시트보기 (PDF) - Analog Devices

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AD8620B
(Rev.:RevD)

Precision, Very Low Noise, Low Input Bias Current, Wide Bandwidth JFET Operational Amplifier

Analog Devices 

AD8610/AD8620

Driving Large Capacitive Loads

The AD8610 has excellent capacitive load driving capability and

can safely drive up to 10 nF when operating with ± 5 V supply.

Figures 4 and 5 compare the AD8610/AD8620 against the OPA627

in the noninverting gain configuration driving a 10 kΩ resistor and

10,000 pF capacitor placed in parallel on its output, with a square

wave input set to a frequency of 200 kHz. The AD8610 has much

less ringing than the OPA627 with heavy capacitive loads.

VS = ؎5V

RL = 10k⍀

CL = 10,000pF

+5V

3

7

VIN = 50mV 2

4

–5V

2␮F

2k⍀

2k⍀

Figure 6. Capacitive Load Drive Test Circuit

VS = ؎5V

RL = 10k⍀

CL = 2␮F

TIME – 2␮s/DIV

Figure 4. OPA627 Driving CL = 10,000 pF

VS = ؎5V

RL = 10k⍀

CL = 10,000pF

TIME – 20␮s/DIV

Figure 7. OPA627 Capacitive Load Drive, AV = +2

VS = ؎5V

RL = 10k⍀

CL = 2␮F

TIME – 2␮s/DIV

Figure 5. AD8610/AD8620 Driving CL = 10,000 pF

The AD8610/AD8620 can drive much larger capacitances without

any external compensation. Although the AD8610/AD8620 is stable

with very large capacitive loads, remember that this capacitive

loading will limit the bandwidth of the amplifier. Heavy capacitive

loads will also increase the amount of overshoot and ringing at the

output. Figures 7 and 8 show the AD8610/AD8620 and the OPA627

in a noninverting gain of +2 driving 2 µF of capacitance load. The

ringing on the OPA627 is much larger in magnitude and continues

more than 10 times longer than the AD8610.

TIME – 20␮s/DIV

Figure 8. AD8610/AD8620 Capacitive Load Drive, AV = +2

Slew Rate (Unity Gain Inverting vs. Noninverting)

Amplifiers generally have a faster slew rate in an inverting unity

gain configuration due to the absence of the differential input

capacitance. Figures 9 through 12 show the performance of the

AD8610 configured in a gain of –1 compared to the OPA627.

The AD8610 slew rate is more symmetrical, and both the positive

and negative transitions are much cleaner than in the OPA627.

–10–

REV. D

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