Datasheet AD1580 (Analog Devices) - 9

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AD1580 TRANSIENT RESPONSE PRECISION MICROPOWER LOW DROPOUT
Many ADC and DAC converters present transient current
REFERENCE
loads to the reference. Poor reference response can degrade The circuit in Figure 24 provides an ideal solution for making the converter’s performance. a stable voltage reference with low standby power consumption, Figure 22 displays both the coarse and fine settling characteristics low input/output dropout capability, and minimum noise output. of the device to load transients of ±50 μA. The amplifier both buffers and optionally scales up the AD1580 output voltage, VR. Output voltages as high as 2.1 V can supply
20mV/DIV 1mV/DIV
1 mA of load current. A one-pole filter connected between the AD1580 and the OP193 input can be used to achieve low output
I
noise. The nominal quiescent power consumption is 200 µW.
R = 100µA + 50µA STEP 3V (a) 34.8kΩ 205Ω OP193 VOUT = +1.225V OR 4.7µF VOUT = +1.225 (1 + R2/R3) (b) IR = 100µA – 50µA STEP AD1580 R3 R2
022
20mV/DIV 1mV/DIV 1µs/DIV
024 00700- Figure 22. Transient Settling 00700- Figure 24. Micropower Buffered Reference Figure 22a shows the settling characteristics of the device for an increased reverse current of 50 μA. Figure 22b shows the
USING THE AD1580 WITH 3 V DATA CONVERTERS
response when the reverse current is decreased by 50 µA. The AD1580 low output drift (50 ppm/°C) and compact submi- The transients settle to 1 mV in about 3 µs. niature SOT-23 package make it ideally suited for today’s high Attempts to drive a large capacitive load (in excess of 1000 pF) may performance converters in space critical applications. result in ringing, as shown in the step response (see Figure 23). One family of ADCs for which the AD1580 is wel suited is the This is due to the additional poles formed by the load capacit- AD7714-3 and AD7715-3. The AD7714/AD7715 are charge- ance and the output impedance of the reference. A recommended balancing ( ∑-∆) ADCs with on-chip digital filtering intended for method of driving capacitive loads of this magnitude is shown the measurement of wide dynamic range, low frequency signals in Figure 20. A resistor isolates the capacitive load from the such as those representing chemical, physical, or biological output stage, while the capacitor provides a single-pole low-pass processes. Figure 25 shows the AD1580 connected to the filter and lowers the output noise. AD7714-3/AD7715-3 for 3 V operation.
3V 2.0V 34.8kΩ AD7714-3 AND AD7715–3 1.8V VIN REFIN(+) RSW 5kΩ (TYP) HIGH AD1580 IMPEDANCE REFIN(–) >1GΩ CREF (3pF TO 8pF) SWITCHING FREQUENCY DEPENDS
025
ON fCLKIN C
00700-
L = 0.01µF
Figure 25. Reference Circuit for the AD7714-3 and AD7715-3 023
10mV/DIV 50µs/DIV
00700- Figure 23. Transient Response with Capacitive Load Rev. F | Page 9 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