Datasheet ADR1581 (Analog Devices) - 9

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ADR1581
Output turn-on time is modified when an external noise-reduction Attempts to drive a large capacitive load (in excess of 1000 pF) may filter is used. When present, the time constant of the filter dom- result in ringing, as shown in the step response (see Figure 22). This inates the overall settling. is due to the additional poles formed by the load capacitance and the output impedance of the reference. A recommended method
2.4V
of driving capacitive loads of this magnitude is shown in Figure 19.
VIN 0V
A resistor isolates the capacitive load from the output stage, whereas the capacitor provides a single-pole low-pass filter
OUTPUT ERROR 1mV/DIV, 2µs/DIV
and lowers the output noise.
2.0V 1.8V VIN OUTPUT
20
0.5mV/DIV, 2ms/DIV
-0 72 66 0 Figure 20. Turn-On Settling
CL = 0.01µF TRANSIENT RESPONSE
Many ADCs and DACs present transient current loads to the 22 0
10mV/DIV 50µs/DIV
2- reference. Poor reference response can degrade the converter’s 67 06 performance. Figure 22. Transient Response with Capacitive Load Figure 21 displays both the coarse and fine settling characteristics
PRECISION MICROPOWER LOW DROPOUT
of the device to load transients of ±50 μA.
REFERENCE 20mV/DIV 1mV/DIV
The circuit in Figure 23 provides an ideal solution for creating a stable voltage reference with low standby power consumption,
IR = 150µA + 50µA STEP
low input/output dropout capability, and minimum noise output. The amplifier both buffers and optionally scales up the ADR1581
(a)
output voltage. Output voltages as high as 2.1 V can supply 1 mA of load current. A one-pole filter connected between the ADR1581 and the OP193 input can be used to achieve low output noise. The
(b)
nominal quiescent power consumption is 250 μW.
I 3V R = 150µA – 50µA STEP 28.7kΩ
1
205Ω OP193
02
V 20mV/DIV 1mV/DIV 1µs/DIV
2-
OUT = 1.250V
67
OR
06
4.7µF VOUT = 1.250 (1 + R2/R3)
Figure 21. Transient Settling Figure 21a shows the settling characteristics of the device for an increased reverse current of 50 μA. Figure 21b shows the response
ADR1581 R3 R2
23 when the reverse current is decreased by 50 μA. The transients 0 settle to 1 mV in about 3 μs. 06672- Figure 23. Micropower Buffered Reference Rev. 0 | Page 9 of 12 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PIN CONFIGURATION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLYING THE ADR1581 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 ADR1581 WITH 3 V DATA CONVERTERS OUTLINE DIMENSIONS ORDERING GUIDE