ISL21070 Datasheet, PDF (9/12 Pages) Intersil Corporation – 25μA Micropower Voltage References

ISL21070
through that type of screening over 100 times, it may
need to consider shielding with copper or aluminum.
Checked luggage X-rays are higher intensity and can
cause output voltage shift in much fewer passes, thus
devices expected to go through those machines should
definitely consider shielding. Note that just two layers of
1/2 ounce copper planes will reduce the received dose by
over 90%. The leadframe for the device which is on the
bottom also provides similar shielding.
If a device is expected to pass through luggage X-ray
machines numerous times, it is advised to mount a
2-layer (minimum) PC board on the top, and along with a
ground plane underneath will effectively shield it from 50
to 100 passes through the machine. Since these
machines vary in X-ray dose delivered, it is difficult to
produce an accurate maximum pass recommendation.
Noise Performance and Reduction
The output noise voltage in a 0.1Hz to 10Hz bandwidth is
typically 30µV_P-P. 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. Wideband noise is reduced by adding
capacitor to the output, but the value should be limited
to 1nF or less to insure stability.
Temperature Drift
The limits stated for output accuracy over-temperature
are governed by the method of measurement. For the
-40°C to 85°C temperature range, measurements are
made at +25°C and the two extremes. This
measurement method combined with the fact that FGA
references have a fairly linear temperature drift
characteristic insures that the limits stated will not be
exceeded over the temperature range.
Typical Application Circuits
ISL21070 Used as a Low Cost Precision
Current Source
Using an N-JET and the ISL21070, a precision, low cost,
high impedance current source can be created. The
precision of the current source is largely dependent on
the tempco and accuracy of the reference. The current
setting resistor contributes less than 20% of the error.
+8V TO 28V
I_SET
=
V_OUT
R_SET
I_L = I_{SET +} IR_SET
0.01µF
V_{IN VOUT}
ISL21070-2.5
V_OUT = 2.5V ^{ZOUT > 100MΩ}
GND
R_SET
1kΩ
0.1%
10ppm/°C
I_SY ~ 11µA
I_SET
IL AT 0.1% ACCURACY
~2.5011mA
FIGURE 16. ISL21070 USED AS A LOW COST
PRECISION CURRENT SOURCE
V_IN = 3.0V
R = 200Ω
2N2905
V_IN
ISL21070V^OUT
GND
2.5V/50mA
0.001µF
FIGURE 17. PRECISION 2.5V 50mA REFERENCE
9
FN7599.0
March 19, 2010