ISL21080_14 Datasheet, PDF (15/20 Pages) Intersil Corporation – 300nA NanoPower Voltage References

ISL21080
not a major source of output voltage shift, however, if a product is
expected to pass 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.
Nanopower Operation
Reference devices achieve their highest accuracy when powered
up continuously, and after initial stabilization has taken place.
This drift can be eliminated by leaving the power on continuously.
The ISL21080 is the first high precision voltage reference with ultra low
power consumption that makes it possible to leave power on
continuously in battery operated circuits. The ISL21080 consumes
extremely low supply current due to the proprietary FGA technology.
Supply current at room temperature is typically 350nA, which is 1 to 2
orders of magnitude lower than competitive devices. Application
circuits using battery power will benefit greatly from having an accurate,
stable reference, which essentially presents no load to the battery.
In particular, battery powered data converter circuits that would
normally require the entire circuit to be disabled when not in use
can remain powered up between conversions as shown in
Figure 37. Data acquisition circuits providing 12 bits to 24 bits of
accuracy can operate with the reference device continuously
biased with no power penalty, providing the highest accuracy and
lowest possible long term drift.
Other reference devices consuming higher supply currents will need to
be disabled in between conversions to conserve battery capacity.
Absolute accuracy will suffer as the device is biased and requires time
to settle to its final value, or, may not actually settle to a final value as
power on time may be short. Table 1 shows an example of battery life in
years for ISL21080 in various power on condition with 1.5µA maximum
current consumption.
TABLE 1. EXAMPLE OF BATTERY LIFE IN YEARS FOR ISL21080 IN
VARIOUS POWER ON CONDITIONS WITH 1.5µA MAX
CURRENT
BATTERY RATING
(mAH)
CONTINUOUS
50% DUTY
CYCLE
10% DUTY
CYCLE
40
3
6
30*
225
16.3*
32.6*
163*
NOTE: *Typical Li-ion battery has a shelf life of up to 10 years.
V_IN = +3.0V
10µF
V_{IN VOUT}
ISL21080
GND
0.001µF TO 0.01µF
SERIAL
BUS
0.01µF
REF IN
ENABLE
SCK
SDAT
12 TO 24-BIT
A/D CONVERTER
FIGURE 37. REFERENCE INPUT FOR ADC CONVERTER
ISL21080 Used as a Low Cost Precision
Current Source
Using an N-JET and a Nanopower voltage reference, ISL21080, 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.
Board Mounting Considerations
For applications requiring the highest accuracy, board mounting
location should be reviewed. Placing the device in areas subject to
slight twisting can cause degradation of the accuracy of the
reference voltage due to die stresses. It is normally best to place the
device near the edge of a board, or the shortest side, as the axis of
bending is most limited at that location. Obviously, mounting the
device on flexprint or extremely thin PC material will likewise cause
loss of reference accuracy.
+8V TO 28V
I_SET
=
V_OUT
R_SET
I_L = I_{SET +} IR_SET
0.01µF
V_{IN VOUT}
ISL21080-1.5
V_OUT = 1.5V
Z_OUT > 100M
GND
R_SET
10kΩ
0.1%
10ppm/°C
I_SY ~ 0.31µA
I_SET
IL AT 0.1% ACCURACY
~150.3µA
FIGURE 38. ISL21080 USED AS A LOW COST PRECISION CURRENT
SOURCE
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June 23, 2014