X60008E-41 Datasheet, PDF (7/10 Pages) Intersil Corporation – Precision 4.096V FGA Voltage Reference

X60008E-41
APPLICATIONS INFORMATION
FGA Technology
The X60008 series of voltage references use the float-
ing 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 ver-
sion of the floating gate voltage. The resulting refer-
ence device has excellent characteristics which are
unique in the industry: very low temperature drift, high
initial accuracy, and almost zero supply current. Also,
the reference voltage itself is not limited by voltage
bandgaps or zener settings, so a wide range of refer-
ence voltages can be programmed (standard voltage
settings are provided, 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 transis-
tor circuitry. While providing excellent accuracy, there
are limitations in output noise level and load regulation
due to the MOS device characteristics. These limita-
tions are addressed with circuit techniques discussed
in other sections.
Nanopower Operation
Reference devices achieve their highest accuracy
when powered up continuously, and after initial stabili-
zation has taken place. This drift can be eliminated by
leaving the power on continuously.
The X60008 is the first high precision voltage refer-
ence with ultra low power consumption that makes it
practical to leave power on continuously in battery
operated circuits. The X60008 consumes extremely
low supply current due to the proprietary FGA technol-
ogy. 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, sta-
ble 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
acquisition 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 = 4.5–9V
10µF
0.01µF
V_{IN VOUT}
X60008-41
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
REV 1.3 6/9/04
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