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AD688BQ 数据表(PDF) 8 Page - Analog Devices |
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AD688BQ 数据表(HTML) 8 Page - Analog Devices |
8 / 16 page AD688 Rev. B | Page 8 of 16 NOISE PERFORMANCE AND REDUCTION The noise generated by the AD688 is typically less than 6 µV p-p over the 0.1 Hz to 10 Hz band. Noise in a 1 MHz bandwidth is approximately 840 µV p-p. The dominant source of this noise is the buried Zener which contributes approximately 140 nV/√Hz. In comparison, the op amp’s contribution is negligible. Figure 6 shows the 0.1 Hz to 10 Hz noise of a typical AD688. 1 µV 1mV 5s 100 90 10 0% Figure 6. 0.1 Hz to 10 Hz Noise If further noise reduction is desired, an optional capacitor can be added between the noise reduction pin and ground as shown in Figure 5. This will form a low-pass filter with the 5 kΩ RB on the output of the Zener cell. A 1 µF capacitor will have a 3 dB point at 32 Hz and will reduce the high frequency noise (to 1 MHz) to about 250 µV p-p. Figure 7 shows the 1 MHz noise of a typical AD688 both with and without a 1 µF capacitor. 200 µV 50 µs CN = 1µF NO CN Figure 7. Effect of 1 µF Noise Reduction Capacitor on Broadband Noise TURN ON TIME Upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error is the turn on settling time. Two components normally associated with this are: time for active circuits to settle and time for thermal gradients on the chip to stabilize. Figure 8 and Figure 9 show the turn on characteristics of the AD688. They show the settling time to be about 600 µs. Note the absence of any thermal tails when the horizontal scale is expanded to 2 ms/cm in Figure 9. 100 90 10 0% +VS –VS +VOUT 10V 1mV 100 µs 10V Figure 8. Turn On Characteristics: Electrical Turn On 100 90 10 0% +VS –VS +VOUT 10V 1mV 2ms 10V Figure 9. Turn On Characteristics: Extended Time Scale Output turn on time is modified when an external noise reduction capacitor is used. When present, this capacitor presents an additional load to the internal Zener diode’s current source, resulting in a somewhat longer turn on time. In the case of a 1 µF capacitor, the initial turn on time is approximately 100 ms (Figure 10). When the noise reduction feature is used, a 20 kΩ resistor between Pin 6 and Pin 2 is required for proper startup. 100 90 10 0% +VS –VS +VOUT 10V 1mV 20ms 10V Figure 10. Turn On With 1 µF CN |
类似零件编号 - AD688BQ |
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类似说明 - AD688BQ |
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