Datasheet AD1580 (Analog Devices) - 8

link to page 8 link to page 8 link to page 8 link to page 8 link to page 8 link to page 8
AD1580 NOISE PERFORMANCE AND REDUCTION
Upon application of power (cold start), the time required for The noise generated by the AD1580 is typically less than the output voltage to reach its final value within a specified 5 µV p-p over the 0.1 Hz to 10 Hz band. Figure 17 shows the error is the turn-on settling time. Two components normally 0.1 Hz to 10 Hz noise of a typical AD1580. Noise in a 10 Hz to associated with this are time for active circuits to settle and time 10 kHz bandwidth is approximately 20 μV rms (see Figure 18a). for thermal gradients on the chip to stabilize. This characteristic If further noise reduction is desired, a 1-pole low-pass filter can is generated from cold start operation and represents the true be added between the output pin and ground. A time constant turn-on waveform after power-up. Figure 21 shows both the of 0.2 ms has a −3 dB point at about 800 Hz and reduces the coarse and fine turn-on settling characteristics of the device; high frequency noise to about 6.5 μV rms (see Figure 18b). the total settling time to within 1.0 mV is about 6 µs, and there A time constant of 960 ms has a −3 dB point at 165 Hz and is no long thermal tail when the horizontal scale is expanded to reduces the high frequency noise to about 2.9 μV rms (see 2 ms/div. Figure 18c).
2.4V V 0V IN 4.5µV p-p CL = 200pF
019
250mV/DIV 5µs/DIV
00700- 017
1µV/DIV 1s/DIV
Figure 19. Turn-On Response Time 00700- Figure 17. 0.1 Hz to 10 Hz Voltage Noise
RS = 11.5kΩ RL + 40µV/DIV 21µV rms VIN VR CL VOUT
020
– (a)
00700- Figure 20. Turn-On, Settling, and Transient Test Circuit
20µV/DIV 6.5µV rms, τ = 0.2ms
Output turn-on time is modified when an external noise reduction filter is used. When present, the time constant
(b)
of the filter dominates overall settling.
2.4V 10µV/DIV 2.90µV rms, τ = 960ms (c) VIN 0V
018
10ms/DIV
00700-
OUTPUT ERROR
Figure 18. Total RMS Noise
1mV/DIV, 2µs/DIV TURN-ON TIME
Many low power instrument manufacturers are becoming increasingly concerned with the turn-on characteristics of components being used in their systems. Fast turn-on compo- nents often enable the end user to keep power off when not
OUTPUT 0.5mV/DIV, 2ms/DIV
021 needed, and yet those components respond quickly when 00700- the power is turned on for operation. Figure 19 displays the Figure 21. Turn-On Settling turn-on characteristic of the AD1580. Rev. F | Page 8 of 12 Document Outline Features Applications General Description Pin Configurations Revision History Specifications Absolute Maximum Ratings ESD Caution Typical Performance Characteristics Theory of Operation Applying the AD1580 Temperature Performance Voltage Output Nonlinearity vs. Temperature Reverse Voltage Hysteresis Output Impedance vs. Frequency Noise Performance and Reduction Turn-On Time Transient Response Precision Micropower Low Dropout Reference Using the AD1580 with 3 V Data Converters Outline Dimensions Ordering Guide Package Branding Information