isl21060 Intersil Corporation, isl21060 Datasheet - Page 18

• Manufacturer Part Number: isl21060
• Description: Precision Reference With Disable
• Manufacturer: Intersil Corporation

FGA Technology
The ISL21060 voltage reference floating gate references
passes very low drift and supply current. 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 and
include 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 drive. This circuitry
provides excellent accuracy with a trade-off in output noise
level and load regulation due to the MOS device
characteristics. These limitations are addressed with circuit
techniques discussed in other sections.
Micropower Supply Current and Output Enable
The ISL21060 consumes extremely low supply current due
to the proprietary FGA technology. Low noise performance is
achieved using optimized biasing techniques. Supply current
is typically 16µA and noise is 10µV
low noise portable applications, such as handheld meters
and instruments.
The ISL21060 devices have the EN pin, which is used to
Enable/Disable the output of the device. When disabled, the
reference circuitry itself remains biased at a highly accurate
and reliable state. When enabled, the output is driven to the
reference voltage in a relatively short time (about 300µs).
This feature allows multiple references to be connected and
one of them selected. Another application is to disable any
loads that draw significant current, saving power in standby
or shutdown modes.
Board Mounting Considerations
For applications requiring the highest accuracy, board
mounting location should be reviewed. The device uses a
plastic SOIC package, which will subject the die to mild
stresses when the PC board is heated and cooled and
slightly changes shape. Placing the device in areas subject
to slight twisting can cause degradation of the accuracy of
the reference voltage due to these 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. Mounting the device in a cutout also minimizes flex.
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 10µV
P-P
. The noise measurement is made with a
18
P-P
, benefitting precision,
ISL21060
bandpass filter made of a 1-pole high-pass filter with a corner
frequency at 0.1Hz 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
100µV
measurement is 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 10x the center frequency. Load capacitance up
to 1µF can be added to improve transient response.
Turn-On Time
The ISL21060 devices have low supply current and thus the
time to bias-up internal circuitry to final values will be longer
than with higher power references. Normal turn-on time is
typically 300µs. Circuit design must take this into account
when looking at power-up delays or sequencing.
Temperature Coefficient
The limits stated for temperature coefficient (tempco) are
governed by the method of measurement. The overwhelming
standard for specifying the temperature drift of a reference is to
measure the reference voltage at two temperatures take the
total variation, (V
extremes of measurement (T
divided by the nominal reference voltage (at T = +25°C) and
multiplied by 10
specifying temperature coefficient.
VOUT Kelvin Sensing
The voltage output for the ISL21060 has both a force and a
sense output. This enables remote kevin sensing for highly
accurate voltage setting with long traces and higher current
loads. The VOUTF (force) can be routed to the load with the
shortest, widest trace possible. The VOUTS (sense) is routed
with a narrower trace to the point of the actual load where it is
connected to the VOUTF trace.
The VOUTF and VOUTS traces must always be connected.
If there is only a short trace to the load or even a very light
load, then they can be connected at or near the ISL21060
device.
P-P
with no capacitance on the output. This noise
6
HIGH
to yield ppm/°C. This is the “Box” method for
– V
LOW
HIGH
), and divide by the temperature
– T
LOW
). The result is
December 16, 2008
FN6706.3