• No missing codes over full military temperature range
• Edge-triggered, no pipeline delay
• Ideal for both time and frequency-domain applications
GENERAL DESCRIPTION
DATEL's ADS-118 and ADS-118A are 12-bit, 5MHz, sampling
A/D converters packaged in space-saving 24-pin DDIP’s. The
ADS-118 offers an input range of ±1V and has three-state
outputs. The ADS-118A has an input range of ±1.25V and
features direct adjustment of offset error.
These functionally complete low-power devices (1.3 Watts)
contain an internal fast-settling sample/hold amplifier, a 12-bit
subranging A/D converter, a precise voltage reference, timing/
control logic, and error-correction circuitry. All timing and
control logic operates from the rising edge of a single start
convert pulse. Digital input and output levels are TTL. Models
are available for use in either commercial (0 to +70°C) or
military (–55 to +125°C) operating temperature ranges.
Applications include radar, transient signal analysis, process
control, medical/graphic imaging, and FFT spectrum analysis.
+5V Supply (Pins 13, 21)0 to +6Volts
–5V Supply (Pin 20)0 to –6Volts
Digital Input (Pin 16, 17)–0.3 to +V
Analog Input (Pin 19)±5Volts
Lead Temperature (10 seconds)+300°C
Power Dissipation—1.31.5—1.31.5—1.31.5Watts
Power Supply Rejection——±0.1——±0.1——±0.1%FSR/%V
Footnotes:
➀ All power supplies should be on before applying a start convert pulse. All
supplies and the clock (start convert pulses) must be present during warmup
periods. The device must be continuously converting during this time.
➁ Input voltage ranges for ADS-118A is ±1.25V
➂ A 100ns wide start convert pulse is used for all production testing. For
applications requiring less than an 5MHz sampling rate, wider start convert
pulses can be used.
NOTE: The device only requires the rising edge of a start convert pulse to
operate.
➃ Effective bits is equal to:
➄ This is the time required before the A/D output data is valid once the analog input
is back within the specified range.
➅ The minimum supply voltages of +4.9V and –4.9V for ±V
–55°C operation only. The minimum limits are +4.75V and –4.75V when
operating at +125°C
Offset Binary
(SNR + Distortion) – 1.76 + 20 log
Full Scale Amplitude
Actual Input Amplitude
6.02
DD are required for
TECHNICAL NOTES
1. Obtaining fully specified performance from the ADS-118
requires careful attention to pc-card layout and power supply
decoupling. The device’s analog and digital ground systems
are connected to each other internally. For optimal performance, tie all ground pins (14, 18, and 23) directly to a large
analog ground plane beneath the package.
Bypass all power supplies to ground with 4.7µF tantalum
capacitors in parallel with 0.1µF ceramic capacitors. Locate
the bypass capacitors as close to the unit as possible.
2. The ADS-118 achieves its specified accuracies without the
need for external calibration. If required, the device’s small
initial offset and gain errors can be reduced to zero using
the adjustment circuitry shown in Figures 2a and 2b. When
using this circuitry, or any similar offset and gain-calibration
hardware, make adjustments following warmup. To avoid
interaction, always adjust offset before gain.
3. To enable the three-state outputs, connect ENABLE
(pin 17) to a logic "0" (low). To disable, connect pin 17 to
logic "1" (high). The three-state outputs are permanently
enabled in the ADS-118A.
4. Applying a start convert pulse while a conversion is in
progress (EOC = logic "1") will initiate a new and inaccurate
conversion cycle.
3
Page 4
ADS-118/118A
Potentiometer is at 25Ω during the device's factory trim procedure.
–15V (or –5V)
–15V
CALIBRATION PROCEDURE
Any offset and/or gain calibration procedures should not be
implemented until devices are fully warmed up. To avoid
interaction, offset must be adjusted before gain. The ranges of
adjustment for the circuits in Figures 2a and 2b are guaranteed
to compensate for the ADS-118's initial accuracy errors and
may not be able to compensate for additional system errors.
A/D converters are calibrated by positioning their digital
outputs exactly on the transition point between two adjacent
digital output codes. This can be accomplished by connecting
LED’s to the digital outputs and adjusting until certain LED's
"flicker" equally between on and off. Other approaches employ
digital comparators or microcontrollers to detect when the
outputs change from one code to the next.
For the ADS-118, offset adjusting is normally accomplished at
the point where the MSB is a 1 and all other output bits are 0’s
and the LSB just changes from a 0 to a 1. This digital output
transition ideally occurs when the applied analog input is
+½LSB (+244µV for ADS-118; +305µV for ADS-118A).
Gain adjusting is accomplished when all bits are 1’s and the
LSB just changes from a 1 to a 0. This transition ideally occurs
when the analog input is at +full scale minus 1½ LSB's
(+0.99927V for ADS-118; +1.249085V for ADS-118A).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input
(pin 16) so the converter is continuously converting.
2. Apply +244µV (ADS-118) or +305µV (ADS-118A) to the
ANALOG INPUT (pin 19).
®®
3. Adjust the offset potentiometer until the output bits are
1000 0000 00000 and the LSB flickers between 0 and 1.
Gain Adjust Procedure
1. Apply +0.99927V (ADS-118) or +1.249085V (ADS-118A) to
the ANALOG INPUT (pin 19).
2. Adjust the gain potentiometer until all output bits are 1's
and the LSB flickers between 1 and 0.
3. To confirm proper operation of the device, vary the input
signal to obtain the output coding listed in Table 1.
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
A = +25°C) production testing is performed without the use
(T
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.
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
0 250 500 750 1 1.25 1.5 1.75 2 2.25 2.5
kHz kHz kHz MHz MHz MHz MHz MHz MHz MHz
®®
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 AN8, "Heat Sinks for DIP Data Converters",
or contact DATEL directly, for additional information.
Frequency
Figure 5. FFT Analysis of ADS-118
+0.67
0
–0.47
0
Digital Output Code
0
4096
4096
Figure 6. ADS-118 Histogram and Differential Nonlinearity
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Lead Material: Kovar alloy
Lead Finish:
over 100 microinches (nominal) nickel plating
0.600 ±0.010
(unless otherwise indicated):
50 microinches (minimum) gold plating
+0.002
0.010
–0.001
(0.254)
0.100
(15.240)
(2.540)
®®
1.31 MAX.
(33.02)
24-Pin
Surface Mount
Versions
0.190 MAX.
(4.826)
24
PIN 1
INDEX
0.100 TYP.
0.020 TYP.
(0.508)
0.040
13
0.80 MAX.
(20.32)
121
0.100
(2.540)
Dimension Tolerances
2 place decimal (.XX) ±0.010 (±0.254)
3 place decimal (.XXX) ±0.005 (±0.127)
Lead Material: Kovar alloy
Lead Finish: 50 microinches (minimum) gold plating
over 100 microinches (nominal) nickel plating
0.060 TYP.
(1.524)
0.130 TYP.
(3.302)
0.020
(0.508)
MAX. radius
0.010 TYP.
0.015
(0.381)
for any pin
(0.254)
ORDERING INFORMATION
MODEL NUMBER TEMP. RANGEPACKAGE
OPERATING24-PIN
ADS-118MC0 to +70°CDDIP
ADS-118MM–55 to +125°CDDIP
ADS-118AMC0 to +70°CSMT
ADS-118AMM–55 to +125°CSMT
Receptacles for PC board mounting can be ordered through AMP, Inc., Part # 3-331272-8 (Component Lead
Socket), 24 required. For MIL-STD-883 product, or surface mount packaging, contact DATEL.
DATEL makes no representation that the use of its products in the circuits described herein, or the use of other technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein
do not imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.
ISO 9001
DS-0231D 10/96
Loading...
+ hidden pages
You need points to download manuals.
1 point = 1 manual.
You can buy points or you can get point for every manual you upload.