X60008E-50 Datasheet, PDF (9/14 Pages) Intersil Corporation – Precision 5.0V FGA Voltage Reference

X60008E-50
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 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. For example, power-up drift on
a high accuracy reference can reach 20ppm or more
in the first 30 seconds, and generally will settle to a
stable value in 100 hours or so. This drift can be elimi-
nated by leaving the power-on continuously.
The X60008 is the first high precision voltage reference
with ultra low power consumption that makes it possible
to leave power-on continuously in battery operated cir-
cuits. The X60008 consumes extremely low supply cur-
rent 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 refer-
ence 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 = +6-9V
10µF
0.01µF
V_{IN VOUT}
X60008-50
GND
0.001µF-0.01µF
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
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FN8145.0
March 14, 2005