®
®
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
PRODUCT OVERVIEW
The ADS-951 is an 18-bit, 1MHz sampling A/D
converter. This device accurately samples full-scale
input signals up to 100 kHz with no missing codes.
This feature, combined with excellent signal-to-
noise ratio (SNR) and total harmonic distortion (THD),
makes the ADS-951 the ideal choice for both time-
domain (medical imaging, scanners, process control)
and frequency-domain (radar, telecommunications,
spectrum analysis) applications.
Packaged in a 32-pin, side-brazed, metal-sealed,
ceramic TDIP, the functionally complete ADS-951
contains a fast-settling sample-hold amplifier, an
A/D converter, an internal reference, and timing/
control logic. Digital input and output levels are TTL,
and the ADS-951 only requires the rising edge of the
start convert pulse to operate.
The ADS-951 typically dissipates 400mW. The
device is offered with a bipolar (±5V) analog input
range. Models are available for use in commercial
(0 to +70°C), extended (–40 to +110°C), or HI-REL
(–55 to +125°C) operating temperature ranges.
Contact DATEL for converters with input ranges of
±10V (ADS-951-1) or 0 to +10V (ADS-951-2).
PIN
INPUT/OUTPUT CONNECTIONS
FUNCTION
PIN FUNCTION
FEATURES
18-bit resolution
1MHz minimum sampling rate
missing codes over full HI-REL temperature
No
range
low power, 400mW
Very
Small, 32-pin, side-brazed, ceramic TDIP
Edge-triggered, no pipeline delays
Excellent performance
for both time and frequency-domain
Ideal
applications
cost
Low
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
+4.096V REF OUT
ANALOG GROUND
ANALOG INPUT
ANALOG GROUND
OFFSET ADJUST
GAIN ADJUST
DIGITAL GROUND
BIT 18 (LSB)
BIT 17
BIT 16
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
–VA ANALOG SUPPLY
ANALOG GROUND
+5VA ANALOG SUPPLY
+5VD DIGITAL SUPPLY
DIGITAL GROUND
START CONVERT
EOC
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BLOCK DIAGRAM
OFFSET ADJUST 5
25
24
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14
BIT 15
BIT 16
BIT 17
BIT 18 (LSB)
BUFFER
ANALOG INPUT 3
23
22
–
S/H
+
21
20
19
OUTPUT REGISTER
A/D
GAIN ADJUST 6
18
17
16
15
14
13
12
11
10
9
8
GAIN
CIRCUIT
REF
+4.096V REFERENCE OUT 1
START CONVERT 27
EOC 26
TIMING AND
CONTROL LOGIC
30
+5VA ANALOG
SUPPLY
32
–VA ANALOG
SUPPLY
2, 4, 31
ANALOG
GROUND
29
+5VD DIGITAL
SUPPLY
7, 28
DIGITAL
GROUND
Figure 1. ADS-951 Functional Block Diagram
DATEL
•
11 Cabot Boulevard, Mansfield, MA 02048-1151 USA •
Tel: (508) 339-3000
•
www.datel.com
• e-mail: help@datel.com
26 Feb 2014 MDA_ADS-951.C01
Page 1 of 6
®
®
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
UNITS
Volts
Volts
Volts
Volts
Volts
°C
PARAMETERS
Operating Temp. Range, Case
ADS-951MC, MC-C
ADS-951ME, ME-C
ADS-951MM, MM-C
Thermal Impedance
jc
ca
Storage Temperature Range
Package Type
Weight
PHYSICAL/ENVIRONMENTAL
MIN.
TYP.
0
–40
–55
—
—
—
MAX.
+70
+110
+125
UNITS
°C
°C
°C
ABSOLUTE MAXIMUM RATINGS
PARAMETERS
LIMITS
+5VA Supply (Pin 30)
0 to +6
+5VD Supply (Pin 29)
0 to +6
–VA Supply (Pin 32)
0 to –20
Digital Input (Pin 27)
–0.3 to +5VD +0.3
Analog Input (Pin 3)
±7
Lead Temperature (10 seconds)
+300
—
5
—
°C/Watt
—
22
—
°C/Watt
–65
—
+150
°C
32-pin, side-brazed, metal-sealed, ceramic TDIP
0.46 ounces (13 grams)
FUNCTIONAL SPECIFICATIONS
(T
A
= +25°C, +5VA = +5V, –VA = –5V, +5VD = +5V, 1MHz sampling rate, and a minimum 1 minute warmup
➀
unless otherwise specified.)
ANALOG INPUT
Input Voltage Range
Input Resistance
Input Capacitance
DIGITAL INPUT
Logic Levels
Logic "1"
Logic "0"
Logic Loading "1"
Logic Loading "0"
Start Convert Positive Pulse Width
➂
STATIC PERFORMANCE
Resolution
Integral Nonlinearity (fin = 10kHz)
Differential Nonlinearity (fin = 10kHz)
Full Scale Absolute Accuracy
Bipolar Zero Error (Tech Note 2)
Bipolar Offset Error (Tech Note 2)
Gain Error (Tech Note 2)
No Missing Codes (fin = 10kHz)
DYNAMIC PERFORMANCE
Peak Harmonics (–0.5dB)
dc to 100kHz
Total Harmonic Distortion (–0.5dB)
dc to 100kHz
Signal-to-Noise Ratio (w/o distortion, –0.5dB)
dc to 100kHz
Signal-to-Noise Ratio
(& distortion, –0.5dB)
dc to 100kHz
DC Noise
Two-Tone Intermodulation Distortion
(fin = 100kHz, 240kHz, fs = 1MHz, –0.5dB)
Input Bandwidth (–3dB)
Small Signal (–20dB input)
Large Signal (–0.5dB input)
Feedthrough Rejection (fin = 500kHz)
Slew Rate
Aperture Delay Time
Aperture Uncertainty
S/H Acquisition Time ( to ±0.003%FSR, 10V step)
Overvoltage Recovery Time
➄
A/D Conversion Rate
ANALOG OUTPUT
Internal Reference
Voltage
Drift
External Current
MIN.
—
—
—
0 TO +70°C
TYP.
±5
500
7
MAX.
—
—
15
MIN.
—
—
—
–40 TO +110°C
TYP.
±5
500
7
MAX.
—
—
15
MIN.
—
—
—
–55 TO +125°C
TYP.
±5
500
7
MAX.
—
—
15
UNITS
Volts
pF
+2.0
—
—
—
20
—
—
–0.95
—
—
—
—
18
—
—
—
—
500
18
±1.25
±0.3
±0.1
±0.01
±0.1
±0.1
—
—
+0.8
+20
–20
—
—
—
+0.95
±0.4
±0.1
±0.4
±0.4
—
+2.0
—
—
—
20
—
—
–0.95
—
—
—
—
18
—
—
—
—
500
18
±1.25
±0.3
±0.2
±0.03
±0.2
±0.2
—
—
+0.8
+20
–20
—
—
—
+0.95
±0.8
±0.1
±0.8
±0.8
—
+2.0
—
—
—
20
—
—
–0.95
—
—
—
—
18
—
—
—
—
500
18
±1.25
±0.3
±0.4
±0.05
±0.3
±0.4
—
—
+0.8
+20
–20
—
—
—
+0.95
±1.9
±0.15
±0.9
±1.9
—
Volts
Volts
μA
μA
ns
Bits
LSB
LSB
%FSR
%FSR
%FSR
%
Bits
—
—
91
87
—
—
—
—
—
—
—
—
—
—
1
–94
–93
94
91
76
–85
10
5
84
44
5
5
260
500
—
–90
–90
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
91
87
—
—
—
—
—
—
—
—
—
—
1
–94
–93
94
91
76
–85
10
5
84
44
5
5
260
500
—
–90
–90
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1
–93
–92
93
90
76
–81
10
5
84
44
5
5
260
500
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
dB
dB
dB
dB
μVrms
d
MHz
MHz
dB
V/μs
ns
ps rms
ns
ns
MHz
+4.05
—
—
+4.096
±30
—
+4.15
—
0.1
+4.05
—
—
+4.096
±30
—
+4.15
—
0.1
+4.05
—
—
+4.096
±30
—
+4.15
—
0.1
Volts
ppm/°C
mA
DATEL
•
11 Cabot Boulevard, Mansfield, MA 02048-1151 USA •
Tel: (508) 339-3000
•
www.datel.com
• e-mail: help@datel.com
26 Feb 2014 MDA_ADS-951.C01
Page 2 of 6
®
®
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
0 TO +70°C
TYP.
—
—
—
—
MAX.
—
+0.4
–4
+4
MIN.
+2.4
—
—
—
–40 TO +110°C
TYP.
MAX.
MIN.
+2.4
—
—
—
–55 TO +125°C
TYP.
—
—
—
—
MAX.
—
+0.4
–4
+4
UNITS
Volts
Volts
mA
mA
DIGITAL OUTPUTS
Logic Levels
Logic "1"
Logic "0"
Logic Loading "1"
Logic Loading "0"
Output Coding
POWER REQUIREMENTS
Power Supply Ranges
+5VA, +5VD Supplies
–VA Supply
Power Supply Currents
+5VA, +5VD Supplies (total)
–VA Supply
Power Dissipation
Power Supply Rejection
MIN.
+2.4
—
—
—
—
—
—
+0.4
—
–4
—
+4
Complementary Offset Binary
+4.75
–2.8
—
—
—
—
+5.0
–5.0
+75
–4
400
—
+5.25
–18
+90
–15
500
±0.05
+4.75
–2.8
—
—
—
—
+5.0
–5.0
+75
–4
400
±0.05
+5.25
–18
+90
–15
500
—
+4.75
–2.8
—
—
—
—
+5.0
–5.0
+75
–4
400
±0.05
+5.25
–18
+90
–15
500
—
Volts
Volts
mA
mA
mW
%FSR/%V
Footnotes:
➀
All power supplies should be on before applying a start convert pulse. All supplies
and the clock (START CONVERT) must be present during warmup periods. The
device must be continuously converting during this time.
➁
Contact DATEL for other input voltage ranges.
➂
A 1MHz clock with a 500nsec positive pulse width (50% duty cycle) is used for
all production testing. Any duty cycle may be used as long as a minimum positive
pulse width of 20nsec is maintained. For applications requiring lower sampling
rates, clock frequencies lower than 1MHz may be used.
➃
Effective bits is equal to:
(SNR + Distortion) – 1.76 +
20 log
6.02
➄
This is the time required before the A/D output data is valid once the analog input
is back within the specified range.
Full Scale Amplitude
Actual Input Amplitude
DATEL
•
11 Cabot Boulevard, Mansfield, MA 02048-1151 USA •
Tel: (508) 339-3000
•
www.datel.com
• e-mail: help@datel.com
26 Feb 2014 MDA_ADS-951.C01
Page 3 of 6
®
®
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
THERMAL REQUIREMENTS
All DATEL sampling A/D converters are fully characterized and specified
over operating temperature (case) ranges of 0 to +70°C, –40 to +110°C,
and –55 to +125°C. All room-temperature (TA = +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 specifica-
tion tables.
These devices do not normally require heat sinks, however, standard pre-
cautionary 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.
TECHNICAL NOTES
1. Obtaining fully specified performance from the ADS-951 requires careful
attention to pc-card layout and power supply decoupling. The device's ana-
log and digital ground systems are not connected to each other internally.
For optimal performance, tie all ground pins (2, 4, 7, 28, and 31) directly to
a large
analog
ground plane beneath the package.
Bypass all power supplies to ground with 10μF tantalum capacitors in
parallel with 0.1μF ceramic capacitors. Locate the bypass capacitors as
close to the unit as possible. The +4.096V REFERENCE OUTPUT (pin 1)
should not
be bypassed externally. If needed to drive external circuitry, pin
1 should be buffered close to the unit.
2. The ADS-951 achieves its specified accuracies without the need for exter-
nal calibration. If required, the device's small initial errors can be reduced
to zero using the adjustment circuitry shown in Figure 2. When using this
circuitry, or any similar offset and gain calibration hardware, make adjust-
ments following warmup. To avoid interaction, always adjust offset before
gain. Connect pins 5 and 6 to ground if not using offset and gain adjust
circuits.
3. Applying a start convert pulse while a conversion is in progress (EOC =
logic "1") will initiate a new and probably inaccurate conversion cycle. Data
for the interrupted and subsequent conversions will be invalid.
CALIBRATION PROCEDURE
Any offset/gain calibration procedures should not be implemented until the
device is fully warmed up. To avoid interaction, adjust offset before gain.
The ranges of adjustment for the circuits in Figure 2 are guaranteed to
compensate for the ADS-951'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 is
accomplished by connecting LED's to the digital outputs and performing
adjustments 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-951, offset adjusting is normally accomplished when the
analog input is 0 minus ½LSB (–19μV). See Table 2 for the proper bipolar
output coding.
Gain adjusting is accomplished when the analog input is at nominal full
scale minus 1½LSB's (–4.999943V).
Zero/Offset Adjust Procedure
1. Apply a train of pulses to the START CONVERT input (pin 27) so that the
converter is continuously converting.
2. For bipolar zero/offset adjust, apply –19μV to the ANALOG INPUT (pin 3).
3. Adjust the offset potentiometer until the output code flickers equally be-
tween 01 1111 1111 1111 1111 and 10 0000 0000 0000 0000.
Gain Adjust Procedure
1. Apply –4.999943V to the ANALOG INPUT (pin 3).
2. Adjust the gain potentiometer until all output bits are 1's and the LSB flick-
ers between 1 and 0.
3. To confirm proper operation of the device, vary the applied input voltage to
obtain the output coding listed in Table 2.
INPUT VOLTAGE
RANGE
±5V
ZERO ADJUST
(–½ LSB)
–19μV
GAIN ADJUST
(–FS +1½ LSB)
–4.999943
Table 1. Input Connections
COMPLEMENTARY OFFSET BINARY
OUTPUT CODING
BIPOLAR
INPUT RANGE
SCALE
±5V
MSB
LSB
+FS –1 LSB
+4.999962
00 0000 0000 0000 0000
+3/4 FS
+3.750000
00 0111 1111 1111 1111
+1/2 FS
+2.500000
00 1111 1111 1111 1111
0
+0.000000
01 1111 1111 1111 1111
–1/2 FS
–2.500000
10 1111 1111 1111 1111
–3/4 FS
–3.750000
11 0111 1111 1111 1111
–FS +1 LSB
–4.999962
11 1111 1111 1111 1110
–FS
–5.000000
11 1111 1111 1111 1111
Table 2. Output Coding
DATEL
•
11 Cabot Boulevard, Mansfield, MA 02048-1151 USA •
Tel: (508) 339-3000
•
www.datel.com
• e-mail: help@datel.com
26 Feb 2014 MDA_ADS-951.C01
Page 4 of 6
®
®
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
+5VA
ANALOG
+5VA ANALOG
10k
–VA
ANALOG
10k
6
5
26
EOC
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
BIT 1 (MSB)
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
BIT 8
BIT 9
BIT 10
BIT 11
BIT 12
BIT 13
BIT 14
BIT 15
BIT 16
BIT 17
BIT 18 (LSB)
–VA ANALOG
+5VD DIGITAL
10μF
0.1μF
29
GAIN
OFFSET
ADJUST ADJUST
28 DIGITAL
GROUND
7
ADS-951
+5VA ANALOG
10μF
30
+
0.1μF
+
31 ANALOG
GROUND
32
2
4
1 +4.096V
REF. OUT
START CONVERT
27
–VA ANALOG
10μF
0.1μF
ANALOG INPUT
3
Figure 2. Typical ADS-951 Connection Diagram
N
START
CONVERT
500ns typ.
N+1
5ns typ.
INTERNAL S/H
740ns typ.
Hold
Acquisition Time
260ns typ.
65ns typ.
EOC
Conversion Time
730ns typ.
20ns typ.
OUTPUT
DATA
Data N-1 Valid
Invalid Data
Data N Valid
980ns typ.
20ns
N+1
Scale is approximately 50ns per division.
Figure 3. ADS-951 Timing Diagram
DATEL
•
11 Cabot Boulevard, Mansfield, MA 02048-1151 USA •
Tel: (508) 339-3000
•
www.datel.com
• e-mail: help@datel.com
26 Feb 2014 MDA_ADS-951.C01
Page 5 of 6
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