ISL21070 Datasheet, PDF (8/12 Pages) Intersil Corporation – 25μA Micropower Voltage References

ISL21070
Typical Performance Characteristics Curves V_OUT = 2.5V, V_IN = 3V, I_OUT = 0mA, T_A = +25°C
unless otherwise specified. (Continued)
120
100
80
60
40
20
0
1
NO LOAD
1nF LOAD
10nF LOAD
100nF LOAD
10
100
1k
10k 100k 1M
FREQUENCY (Hz)
FIGURE 14. Z_OUT vs f vs C_L
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
1
1nF LOAD
10nF LOAD
NO LOAD
100nF LOAD
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
FIGURE 15. PSRR vs FREQUENCY
Applications Information
FGA Technology
The ISL21070 series of voltage references use 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 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
reference 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 transistor
circuitry. While providing excellent accuracy, there are
limitations in output noise level and load regulation due
to the MOS device characteristics. These limitations are
addressed with circuit techniques discussed in other
sections.
Handling and Board Mounting
FGA references provide excellent initial accuracy and low
temperature drift at the expense of very little power
drain. There are some precautions to take to insure this
accuracy is not compromised. Excessive heat during
solder reflow can cause excessive initial accuracy drift, so
the recommended +260°C max temperature profile
should not be exceeded. Expect up to 1mV drift from the
solder reflow process.
FGA references are susceptible to excessive
X-radiation like that used in PC board manufacturing.
Initial accuracy can change 10mV or more under
extreme radiation. If an assembled board needs to be
X-rayed, care should be taken to shield the FGA
reference device.
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.
Board Assembly Considerations
FGA references provide high accuracy and low
temperature drift but some PC board assembly
precautions are necessary. Normal Output voltage shifts
of 100µV to 1mV can be expected with Pb-free reflow
profiles or wave solder on multi-layer FR4 PC boards.
Precautions should be taken to avoid excessive heat or
extended exposure to high reflow or wave solder
temperatures, this may reduce device initial accuracy.
Post-assembly x-ray inspection may also lead to
permanent changes in device output voltage and should
be minimized or avoided. If x-ray inspection is required,
it is advisable to monitor the reference output voltage to
verify excessive shift has not occurred. If large amounts
of shift are observed, it is best to add an X-ray shield
consisting of thin zinc (300µm) sheeting to allow clear
imaging, yet block x-ray energy that affects the FGA
reference.
Special Applications Considerations
In addition to post-assembly examination, there are also
other X-ray sources that may affect the FGA reference
long term accuracy. Airport screening machines contain
X-rays and will have a cumulative effect on the voltage
reference output accuracy. Carry-on luggage screening
uses low level X-rays and is not a major source of output
voltage shift, however, if a product is expected to pass
8
FN7599.0
March 19, 2010