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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 Nyquist frequencies 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 frequencydomain (radar, telecommunications, spectrum analysis) applications. Packaged in a 32-pin, metal-sealed, ceramic TDIP, the functionally complete ADS-951 contains a fast-settling sample-hold amplifier, a subranging (two-pass) A/D converter, an internal reference, timing/control logic, and error-correction circuitry. Digital input and output levels are TTL, and the ADS-951 only requires the rising edge of the start convert pulse to operate. Requiring 15V and 5V supplies, the ADS951 typically dissipates 1.45 Watts. The device is offered with a bipolar (5V) analog input range. Models are available for use in either commercial (0 to +70C) or extended (-40 to +110C) operating temperature ranges. A proprietary, auto-calibrating, error-correcting circuit enables the device to achieve specified performance over the full HI-REL temperature range.
PIN INPUT/OUTPUT CONNECTIONS FUNCTION PIN FUNCTION
FEATURES

18-bit resolution 1MHz minimum sampling rate No missing codes over extended temperature range Very low power, 1.45 Watts Small, 32-pin, side-brazed, ceramic TDIP Edge-triggered Excellent performance Ideal for both time and frequency-domain applications Low cost

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
BIT 2 BIT 1 (MSB) ANALOG GROUND ANALOG INPUT +5V REFERENCE OUT GAIN ADJUST COMPENSATION -15V SUPPLY +15V SUPPLY +5V ANALOG SUPPLY -5V ANALOG SUPPLY ANALOG GROUND DIGITAL GROUND +5V DIGITAL SUPPLY EOC START CONVERT
32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17
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)
BLOCK DIAGRAM
2 1 BIT 1 (MSB) BIT 2
BUFFER
ANALOG INPUT 4
32 BIT 3
- S/H +
FLASH ADC 1
DIGITAL CORRECTION LOGIC
31 BIT 4 30 BIT 5 29 BIT 6 28 BIT 7 27 BIT 8 26 BIT 9 25 BIT 10 24 BIT 11 23 BIT 12 22 BIT 13 21 BIT 14 20 BIT 15 19 BIT 16 18 BIT 17 17 BIT 18 (LSB)
GAIN ADJUST 6
GAIN CIRCUIT
REF DAC
+5V REFERENCE OUT 5 COMPENSATION 7
AMP
FLASH ADC 2
START CONVERT 16 EOC 15
TIMING AND CONTROL LOGIC
10 +5V ANALOG SUPPLY
11 -5V ANALOG SUPPLY
3, 12 ANALOG GROUND
14 +5V DIGITAL SUPPLY
9 +15V SUPPLY
8 -15V SUPPLY
13 DIGITAL GROUND
For full details go to www.murata-ps.com/rohs
Figure 1. ADS-951 Functional Block Diagram
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MDA_ADS-951.B01 Page 1 of 6
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
ABSOLUTE MAXIMUM RATINGS PARAMETERS LIMITS +15V Supply (Pin 9) 0 to +16 -15V Supply (Pin 8) 0 to -16 +5V Supply (Pins 10, 14) 0 to +6 -5V Supply (Pin 11) 0 to -6 Digital Input (Pin 16) -0.3 to +VDD +0.3 Analog Input (Pin 4) 15 Lead Temperature (10 seconds) +300 UNITS Volts Volts Volts Volts Volts Volts C PARAMETERS Operating Temp. Range, Case ADS-951MC ADS-951ME Thermal Impedance Tjc Tca Storage Temperature Range Package Type Weight PHYSICAL/ENVIRONMENTAL MIN. TYP. 0 -40 -- -- MAX. +70 +110 UNITS C C
-- 5 -- C/Watt -- 22 -- C/Watt -65 -- +150 C 32-pin, metal-sealed, ceramic TDIP 0.46 ounces (13 grams)
FUNCTIONAL SPECIFICATIONS
(TA = +25C, VCC = 15V, VDD = 5V, 1MHz sampling rate, and a minimum 1 minute warmup unless otherwise specified.)
ANALOG INPUT MIN. -- Input Voltage Range d Input Resistance -- Input Capacitance -- DIGITAL INPUT Logic Levels Logic "1" +2.0 Logic "0" -- Logic Loading "1" -- Logic Loading "0" -- 20 Start Convert Positive Pulse Width STATIC PERFORMANCE Resolution -- Integral Nonlinearity (fin = 10kHz) -- Differential Nonlinearity (fin = 10kHz) -0.95 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) 18 DYNAMIC PERFORMANCE (500kHz SAMPLING RATE) 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 91 Signal-to-Noise Ratio f (& distortion, -0.5dB) dc to 100kHz 76 DC Noise -- Two-Tone Intermodulation Distortion (fin = 100kHz, 240kHz, fs = 500kHz, -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 A/D Conversion Rate 1 ANALOG OUTPUT Internal Reference Voltage +4.95 Drift -- External Current -- +25C TYP. 5 500 7 MAX. -- -- 15 MIN. -- -- -- 0 TO +70C TYP. 5 500 7 MAX. -- -- 15 MIN. -- -- -- -40 TO +110C TYP. 5 500 7 MAX. -- -- 15 UNITS Volts : pF
-- -- -- -- 500 18 10 0.5 0.1 0.1 0.1 0.1 --
-- +0.8 +20 -20 -- -- -- +1 0.25 0.15 0.2 0.25 --
+2.0 -- -- -- 20 -- -- -0.95 -- -- -- -- 18
-- -- -- -- 500 18 10 0.5 0.25 0.15 0.2 0.25 --
-- +0.8 +20 -20 -- -- -- +1 0.4 0.25 0.3 0.4 --
+2.0 -- -- -- 20 -- -- -0.95 -- -- -- -- 18
-- -- -- -- 500 18 15 0.50 0.4 0.25 0.3 0.4 --
-- +0.8 +20 -20 -- -- -- +1.25 0.8 0.5 0.6 0.9 --
Volts Volts A A ns Bits LSB LSB %FSR %FSR %FSR % Bits
-87 -85 93 84 76 -85 TBD TBD 84 TBD +20 5 260 500 --
-80 -80 -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- 91 76 -- -- -- -- -- -- -- -- -- -- 1
-87 -85 93 84 76 -85 TBD TBD 84 TBD +20 5 260 500 --
-80 -80 -- -- -- -- -- -- -- -- -- -- -- -- --
-- -- -- -- -- -- -- -- -- -- -- -- -- -- 1
-82 -81 92 80 76 -81 TBD TBD 84 TBD +20 5 260 500 --
-- -- -- -- -- -- -- -- -- -- -- -- -- -- --
dB dB dB dB Vrms d MHz MHz dB V/s ns ps rms ns ns MHz
+5.0 30 1
+5.05 -- --
+4.95 -- --
+5.0 30 1
+5.05 -- --
+4.95 -- --
+5.0 30 1
+5.05 -- --
Volts ppm/C mA
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MDA_ADS-951.B01 Page 2 of 6
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
DIGITAL OUTPUTS Logic Levels Logic "1" Logic "0" Logic Loading "1" Logic Loading "0" Output Coding POWER REQUIREMENTS Power Supply Ranges +15V Supply -15V Supply +5V Supply -5V Supply Power Supply Currents +15V Supply -15V Supply +5V Supply -5V Supply Power Dissipation Power Supply Rejection MIN. +2.4 -- -- -- +25C TYP. -- -- -- -- MAX. -- +0.4 -4 +4 MIN. +2.4 -- -- -- 0 TO +70C TYP. MAX. MIN. +2.4 -- -- -- -40 TO +110C TYP. -- -- -- -- MAX. -- +0.4 -4 +4 UNITS Volts Volts mA mA
-- -- -- +0.4 -- -4 -- +4 Complementary Offset Binary
+14.5 -14.5 +4.75 -4.75 -- -- -- -- -- --
+15.0 -15.0 +5.0 -5.0 +29 -15 +104 -54 1.45 --
+15.5 -15.5 +5.25 -5.25 -- -- -- -- 1.65 0.05
+14.5 -14.5 +4.75 -4.75 -- -- -- -- -- --
+15.0 -15.0 +5.0 -5.0 +29 -15 +104 -54 1.45 --
+15.5 -15.5 +5.25 -5.25 -- -- -- -- 1.65 0.05
+14.5 -14.5 +4.75 -4.75 -- -- -- -- -- --
+15.0 -15.0 +5.0 -5.0 +29 -15 +104 -54 1.45 --
+15.5 -15.5 +5.25 -5.25 -- -- -- -- 1.65 0.05
Volts Volts Volts Volts mA mA mA mA Watts %FSR/%V
Footnotes: 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. Contact DATEL for other input voltage ranges. 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.
Effective bits is equal to: (SNR + Distortion) - 1.76 + 20 log 6.02 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
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MDA_ADS-951.B01 Page 3 of 6
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
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 analog and digital ground systems are not connected to each other internally. For optimal performance, tie all ground pins (3, 12 and 13) directly to a large analog ground plane beneath the package. Bypass all power supplies and the +5V REFERENCE OUTPUT (pin 5) to ground with 10F tantalum capacitors in parallel with 0.1F ceramic capacitors. Locate the bypass capacitors as close to the unit as possible. Tie a 47F capacitor between COMPENSATION (pin 7) and ground. 2. The ADS-951 achieves its specified accuracies without the need for external 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 adjustments following warmup. To avoid interaction, always adjust offset before gain. Float pin 6 if not using 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.
THERMAL REQUIREMENTS
All DATEL sampling A/D converters are fully characterized and specified over operating temperature (case) ranges of 0 to +70C and -40 to +110C. All room-temperature (TA = +25C) 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. Electricallyinsulating, 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.
CALIBRATION PROCEDURE
Connect the converter per Table 1 for the appropriate input voltage range. 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 1/2LSB (-19V). See Table 2 for the proper bipolar output coding. Gain adjusting is accomplished when the analog input is at nominal full scale minus 11/2LSB's (-4.999943V). Zero/Offset Adjust Procedure 1. Apply a train of pulses to the START CONVERT input (pin 16) so that the converter is continuously converting. 2. For bipolar zero/offset adjust, apply -19V to the ANALOG INPUT (pin 4). 3. Adjust the offset potentiometer until the output code flickers equally between 01 1111 1111 1111 1111 and 10 0000 0000 0000 0000.
Gain Adjust Procedure 1. Apply -4.999943V to the ANALOG INPUT (pin 4). 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 applied input voltage to obtain the output coding listed in Table 2.
INPUT VOLTAGE RANGE 5V ZERO ADJUST (-1/2 LSB) -19V GAIN ADJUST (-FS +11/2 LSB) -4.999943
Table 1. Input Connections
COMPLEMENTARY OFFSET BINARY OUTPUT CODING INPUT RANGE 5V MSB LSB +4.999962 00 0000 0000 0000 0000 +3.750000 00 0111 1111 1111 1111 +2.500000 00 1111 1111 1111 1111 +0.000000 01 1111 1111 1111 1111 -2.500000 10 1111 1111 1111 1111 -3.750000 11 0111 1111 1111 1111 -4.999962 11 1111 1111 1111 1110 -5.000000 11 1111 1111 1111 1111
BIPOLAR SCALE +FS -1 LSB +3/4 FS +1/2 FS 0 -1/2 FS -3/4 FS -FS +1 LSB -FS
Table 2. Output Coding
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MDA_ADS-951.B01 Page 4 of 6
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
Pin 5 (ADS-951)
10k
6 GAIN ADJUST
15 EOC 2 BIT 1 (MSB) 1 BIT 2 32 BIT 3 31 30 29 28 27 26 25 24 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)
+5V DIGITAL 10F 0.1F
14
13 DIGITAL GROUND 8
-15V
+
10F
0.1F
12 ANALOG GROUND 9
+15V
10F
0.1F
+
ADS-951
+5V ANALOG 10F
10 + 0.1F + 3 ANALOG GROUND 11 5 +5V REF. OUT ANALOG INPUT 0.1F 10F START CONVERT COMPENSATION 16 7 4
23 22 21 20 19 18 17
-5V ANALOG
10F
0.1F
47F +
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-2 Valid
Invalid Data Data N-1 Valid 980ns typ.
20ns N
Scale is approximately 50ns per division.
Figure 3. ADS-951 Timing Diagram
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MDA_ADS-951.B01 Page 5 of 6
ADS-951
18-Bit, 1MHz, Low-Power Sampling A/D Converters
MECHANICAL DIMENSIONS INCHES (mm)
1.72 MAX. (43.69)
32
17
Dimension Tolerances (unless otherwise indicated): 2 place decimal (.XX) 0.010 (0.254) 3 place decimal (.XXX) 0.005 (0.127) Lead Material: Kovar alloy
1.11 MAX. (28.19)
Lead Finish: 50 microinches (minimum) gold plating over 100 microinches (nominal) nickel plating
1
16
0.235 MAX. (5.969)
0.100 TYP. (2.540) 1.500 (38.100) 0.200 MAX. (5.080)
0.010 -0.001 (0.254) 0.190 MAX. (4.826) 0.018 0.002 (0.457) 0.100 (2.540) 0.040 (1.016) SEATING PLANE 0.025 (0.635)
+0.002
0.900 0.010 (22.860)
0.100 (2.540)
ORDERING INFORMATION MODEL NUMBER ADS-951MC ADS-951ME OPERATING TEMP. RANGE 0 to +70C -40 to +110C 32-PIN PACKAGE TDIP TDIP ADS-B951 ACCESSORIES Evaluation Board (without ADS-951)
Receptacles for PC mounting can be ordered through AMP Inc., Part # 3-331272-8 (Component Lead Socket), 32 required. For availability of MIL-STD-883 product, contact DATEL.
Murata Power Solutions, Inc. 11 Cabot Boulevard, Mansfield, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
Murata Power Solutions, Inc. 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. (c) 2009 Murata Power Solutions, Inc.
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