X60003B-41_06 Datasheet, PDF (7/11 Pages) Intersil Corporation – Precision 4.096V SOT-23 FGA™ Voltage References

X60003B-41, X60003C-41, X60003D-41
APPLICATIONS INFORMATION
FGA Technology
The X60003x-41 voltage reference uses the floating
gate technology to create references with very low drift
and supply current. Essentially the charge stored on a
floating gate cell is set precisely in manufacturing. The
reference voltage output itself is a buffered version of
the floating gate voltage. The resulting reference device
has excellent characteristics which are unique in the
industry: very low temperature drift, high initial accu-
racy, and almost zero supply current. Also, the refer-
ence voltage itself is not limited by voltage bandgaps or
zener settings, so a wide range of reference voltages
can be programmed (standard voltage settings are pro-
vided, but customer-specific voltages are available).
The process used for these reference devices is a
floating gate CMOS process, and the amplifier circuitry
uses CMOS transistors for amplifier and output tran-
sistor circuitry. While providing excellent accuracy,
there are limitations in output noise level and load reg-
ulation due to the MOS device characteristics. These
limitations are addressed with circuit techniques dis-
cussed in other sections.
Nanopower Operation
Reference devices achieve their highest accuracy
when powered up continuously, and after initial stabili-
zation has taken place.
The X60003x-41 is the first high precision voltage ref-
erence with ultra low power consumption that makes it
practical to leave power-on continuously in battery
operated circuits. The X60003x-41 consumes
extremely low supply current due to the proprietary
FGA technology. Supply current at room temperature
is typically 500nA 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 dis-
abled when not in use can remain powered up
between conversions as shown in figure 1. Data acqui-
sition circuits providing 12 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 cur-
rents 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 set-
tle to its final value, or, may not actually settle to a final
value as power-on time may be short.
Figure 1.
V_IN = 4.5V - 9V
10µF
0.01µF
V_{IN VOUT}
X60003x-41
GND
0.001µF
Serial
Bus
REF IN
Enable
SCK
SDAT
12 to 24-bit
A/D Converter
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.
Noise Performance and Reduction:
The output noise voltage in a 0.1Hz to 10Hz
bandwidth is typically 30µVp-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
.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 400µVp-p with no capacitance on the
output, as shown in Fig. 2 below. 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 2 also shows the noise in the
10KHz to 1MHz band can be reduced to about 50µVp-
p using a .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
7
FN8138.1
May 2, 2006