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ADS-941
TECHNICAL NOTES
1. Rated performance requires using good high-frequency
circuit board layout techniques. The analog and digital
grounds are not connected to each other internally. Avoid
ground-related problems by connecting the digital and
analog grounds to one point, the ground plane beneath the
converter. Due to the inductance and resistance of the
power supply return paths, return the analog and digital
ground separately to the power supplies.
2. Bypass the analog and digital supplies and the +10V REF.
OUT (pin 1) to ground with a 4.7µF, 25V tantalum electro-
lytic capacitor in parallel with a 0.1µF ceramic capacitor.
3. CODING SELECT (pin 8) is compatible with CMOS/TTL
logic levels for those users desiring logic control of this
function. The device has an internal pull-up resistor on this
pin, allowing pin 8 to be connected to +5V or left open when
a logic 1 is needed. See the Calibration Procedure for
selecting an output coding.
4. To enable the three-state outputs, connect ENABLE (pin 9)
to a logic "0" (low). To disable, connect pin 9 to a logic "1"
(high).
tied low for straight binary/offset binary or between 00 0000
0000 0000 and 00 0000 0000 0001 with pin 8 tied high for
complementary binary/complementary offset binary.
Two's complement coding requires using pin 31. With pin 8
tied low, adjust the gain trimpot until the output code flickers
equally between 01 1111 1111 1110 and 01 1111 1111 1111.
4. To confirm proper operation of the device, vary the precision
reference voltage source to obtain the output coding listed
in Table 3.
Table 1. Input Connections
INPUT RANGE
0 +10V
±5V
INPUT PIN
Pin 3
Pin 3
TIE TOGETHER
Pins 2 and 4
Pins 1 and 2
Table 2. Zero and Gain Adjustments
Input
Range
0 to +10V
±5V
Zero Adjust
+1/2 LSB
+305µV
+305µV
Gain Adjust
FS – 1 1/2 LSB
+9.999085V
+4.999085V
CALIBRATION PROCEDURE
1. Connect the converter per Figure 3 and Table 1 for the
appropriate input range. Apply a pulse of 50 nanoseconds
minimum to START CONVERT (pin 32) at a rate of 200kHz.
This rate is chosen to reduce flicker if LED's are used on
the outputs for calibration purposes.
2.
Zero Adjustments
Apply a precision voltage reference source between
ANALOG INPUT (pin 3) and SIGNAL GROUND (pin 4),
then adjust the reference source output per Table 2.
For unipolar operation, adjust the zero trimpot so that the
output code flickers equally between 00 0000 0000 0000
and 00 0000 0000 0001 with CODING SELECT (pin 8) tied
low (straight binary) or between 11 1111 1111 1111 and 11
1111 1111 1110 with pin 8 tied high (complementary binary).
For bipolar operation, adjust the trimpot until the code
flickers equally between 10 0000 0000 0000 and 10 0000
0000 0001 with pin 8 tied low (offset binary) or between 01
1111 1111 1111 and 01 1111 1111 1110 with pin 8 tied high
(complementary offset binary).
Two's complement coding requires using BIT 1 OUT (MSB)
(pin 31). With pin 8 tied low, adjust the trimpot until the
code flickers between 00 0000 0000 0000 and 00 0000
0000 0001.
3.
Full-Scale Adjustment
Set the output of the voltage reference used in step 2 to the
value shown in Table 2.
Adjust the gain trimpot until the output code flickers equally
between 11 1111 1111 1110 and 11 1111 1111 1111 with pin 8
THERMAL REQUIREMENTS
All DATEL sampling A/D converters are fully characterized and
specified over operating temperature (case) ranges of 0 to
+70°C and –55 to +125°C. All room-temperature (T
A
= +25°C)
production testing is performed without the use of heat sinks or
forced-air cooling. Thermal impedance figures for each device
are listed in their respective specification tables.
These devices do not normally require heat sinks, however,
standard precautionary design and layout procedures should
be used to ensure devices do not overheat. The ground and
power planes beneath the package, as well as all pcb signal
runs to and from the device, should be as heavy as possible to
help conduct heat away from the package. Electrically-
insulating, thermally-conductive "pads" may be installed
underneath the package. Devices should be soldered to
boards rather than "socketed", and of course, minimal air flow
over the surface can greatly help reduce the package
temperature.
In more severe ambient conditions, the package/junction
temperature of a given device can be reduced dramatically
(typically 35%) by using one of DATEL's HS Series heat sinks.
See Ordering Information for the assigned part number. See
page 1-183 of the DATEL Data Acquisition Components
Catalog for more information on the HS Series. Request
DATEL Application Note AN-8, "Heat Sinks for DIP Data
Converters", or contact DATEL directly, for additional
information.
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