ISL60002_0712 Datasheet, PDF (33/35 Pages) Intersil Corporation – Precision Low Power FGA™ Voltage References

ISL60002
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 Curves. 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 117. 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 117 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 118 is recommended. This network reduces
noise significantly over the full bandwidth. As shown in
Figure 117, noise is reduced to less than 40µV_P-P from 1Hz
to 1MHz using this network with a 0.01µF capacitor and a
2kΩ resistor in series with a 10µF capacitor.
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
100k
FIGURE 117. NOISE REDUCTION
V_IN = 3.0V
0.1µF
10µF
V_IN
V_O
ISL60002-25
VOUT = 2.50V
GND
0.01µF
2kΩ
10µF
FIGURE 118.
Turn-On Time
The ISL60002 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 119. 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.
3.5
3.0
V_IN
2.5
2.0
UNIT 3
1.5
1.0
UNIT 1
UNIT 2
0.5
0
-1
1
3
5
7
TIME (ms)
9
11
3.5
V_IN
3.0
2.5
2.0
UNIT 3
UNIT 1
1.5
1.0
UNIT 2
0.5
0
-1
1
3
5
7
TIME (ms)
9
11
FIGURE 119. TURN-ON TIME
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 measurement
(T_HIGH – T_LOW). The result is divided by the nominal
reference voltage (at T = +25°C) and multiplied by 10⁶ to
yield ppm/°C. This is the “Box” method for specifying
temperature coefficient.
33
FN8082.13
December 17, 2007