ADR1581 Analog Devices, Inc., ADR1581 Datasheet - Page 9

• Manufacturer Part Number: ADR1581
• Description: 1.25 V Micropower, Precision Shunt Voltage Reference
• Manufacturer: Analog Devices, Inc.

Output turn-on time is modified when an external noise-reduction
filter is used. When present, the time constant of the filter dom-
inates the overall settling.
TRANSIENT RESPONSE
Many ADCs and DACs present transient current loads to the
reference. Poor reference response can degrade the converter’s
performance.
Figure 21 displays both the coarse and fine settling characteristics
of the device to load transients of ±50 μA.
Figure 21a shows the settling characteristics of the device for an
increased reverse current of 50 μA. Figure 21b shows the response
when the reverse current is decreased by 50 μA. The transients
settle to 1 mV in about 3 μs.
V
IN
2.4V
20mV/DIV
20mV/DIV
0V
Figure 21. Transient Settling
Figure 20. Turn-On Settling
1mV/DIV
1mV/DIV
I
I
R
R
= 150µA – 50µA STEP
= 150µA + 50µA STEP
OUTPUT ERROR
1mV/DIV, 2µs/DIV
OUTPUT
0.5mV/DIV, 2ms/DIV
1µs/DIV
(a)
(b)
Rev. 0 | Page 9 of 12
Attempts to drive a large capacitive load (in excess of 1000 pF) may
result in ringing, as shown in the step response (see Figure 22). This
is due to the additional poles formed by the load capacitance and
the output impedance of the reference. A recommended method
of driving capacitive loads of this magnitude is shown in
A resistor isolates the capacitive load from the output stage,
whereas the capacitor provides a single-pole low-pass filter
and lowers the output noise.
PRECISION MICROPOWER LOW DROPOUT
REFERENCE
The circuit in Figure 23 provides an ideal solution for creating
a stable voltage reference with low standby power consumption,
low input/output dropout capability, and minimum noise output.
The amplifier both buffers and optionally scales up the ADR1581
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
nominal quiescent power consumption is 250 μW.
3V
ADR1581
28.7kΩ
1.8V
2.0V
Figure 22. Transient Response with Capacitive Load
205Ω
Figure 23. Micropower Buffered Reference
10mV/DIV
4.7µF
R3
R2
V
IN
OP193
50µs/DIV
V
OR
V
C
OUT
OUT
L
= 0.01µF
= 1.250V
= 1.250 (1 + R2/R3)
ADR1581
Figure 19.