ISL21080_14 Datasheet, PDF (16/20 Pages) Intersil Corporation – 300nA NanoPower Voltage References

ISL21080
Noise Performance and Reduction
The output noise voltage in a 0.1Hz to 10Hz bandwidth is
typically 30µV_P-P. This is shown in the plot in the “Typical
Performance Characteristics Curves” which begin on page 10.
The noise measurement is made with a bandpass filter made of
a 1-pole high-pass filter with a corner frequency at 0.1Hz and a
2-pole low-pass filter with a corner frequency at 12.6Hz to create
a filter with a 9.9Hz bandwidth. Noise in the 10kHz to 1MHz
bandwidth is approximately 400µV_P-P with no capacitance on
the output, as shown in Figure 39. These noise measurements
are made with a 2 decade bandpass filter made of a 1-pole
high-pass filter with a corner frequency at 1/10 of the center
frequency and 1-pole low-pass filter with a corner frequency at
10 times the center frequency. Figure 39 also shows the noise in
the 10kHz to 1MHz band can be reduced to about 50µV_P-P using
a 0.001µF capacitor on the output. Noise in the 1kHz to 100kHz
band can be further reduced using a 0.1µF capacitor on the
output, but noise in the 1Hz to 100Hz band increases due to
instability of the very low power amplifier with a 0.1µF
capacitance load. For load capacitances above 0.001µF, the
noise reduction network shown in Figure 40 is recommended.
This network reduces noise significantly over the full bandwidth.
As shown in Figure 39, noise is reduced to less than 40µV_P-P
from 1Hz to 1MHz using this network with a 0.01µF capacitor
and a 2k resistor in series with a 10µF capacitor.
Turn-On Time
The ISL21080 devices have ultra-low supply current and thus, the
time to bias-up internal circuitry to final values will be longer than
with higher power references. Normal turn-on time is typically
7ms. This is shown in Figure 38. Since devices can vary in supply
current down to >300nA, turn-on time can last up to about 12ms.
Care should be taken in system design to include this delay
before measurements or conversions are started.
Temperature Coefficient
The limits stated for temperature coefficient (tempco) are governed
by the method of measurement. The overwhelming standard for
specifying the temperature drift of a reference, is to measure the
reference voltage at two temperatures, take the total variation,
(V_HIGH - V_LOW), and divide by the temperature extremes of
mrefeearseunrceemveonltta(gTe_{H(IGatHT–=T+LO2W5°).CT)haenrdesmuultltisipdliievdidbeyd1b0y6}thtoe
nominal
yield
ppm/°C. This is the “Box” method for specifying temperature
coefficient.
400
350
300
250
200
150
100
50
0
1
CL = 0
CL = 0.001µF
CL = 0.1µF
CL = 0.01µF AND 10µF + 2kΩ
10
100
1k
10k
FIGURE 39. NOISE REDUCTION
100k
V_IN = 3.0V
0.1µF
10µF
V_IN
ISL21080^VO
GND
0.01µF
FIGURE 40. NOISE REDUCTION NETWORK
2kΩ
10µF
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June 23, 2014