NSC CLC949ACQ Very low-power, 12-bit, 20msps monolithic a/d convertter Datasheet

N
Comlinear CLC949
Very Low-Power, 12-Bit,
20MSPS Monolithic A/D Convertter
General Description
Features
The Comlinear CLC949 is a 12-bit analog-to-digital converter subsystem including 12-bit quantizer, sample-and-hold amplifier, and
internal reference. The CLC949 has been optimized for low power
operation with high dynamic range. The CLC949 has a unique
feature which allows the user to adjust internal bias levels in the
converter which results in a trade-off between power dissipation
and maximum conversion rate. With bias set for 220mW power
dissipation the converter operates at 20MSPS. Under these
conditions, dynamic performance with a 9.9MHz analog input is
typically 68dB SNR and 72dBc SFDR. When bias is set for only
65mW power dissipation the converter maintains excellent performance at 5MSPS. With a 2.4MHz analog input signal the SNR is
70dB and SFDR is 78dBc. This excellent dynamic performance in
the frequency domain without high power requirements make the
part a strong performer for communications and radar applications.
The low input noise of the CLC949, its 0.5LSB differential linearity
error specification, fast settling, and low power dissipation also
lead to excellent performance in imaging systems. All parts are
thoroughly tested to insure that guaranteed specifications are met.
■
The CLC949 incorporates an input sample-and-hold amplifier
followed by a quantizer which uses a pipelined architecture to minimize comparator count and the associated power dissipation
penalty. An on-board voltage reference is provided. Analog input
signals, conversion clock, and a single supply are all that are
required for CLC949 operation.
■
For applications requiring high temperature operation and very low
distortion with high frequency input signals, use of an external
sample-and-hold amplifier may enhance performance by reducing
the slew rates that the CLC949 sees during its sampling period (just
after the falling edge of CLK).
The CLC949 is fabricated in a 0.9µm CMOS technology. The
CLC949ACQ is specified over the commercial temperature range
of 0°C to +70°C and the CLC949AJQ is specified over the industrial range of -40°C to +85°C. Both are packaged in a 44-pin
Plastic Leaded Chip Carrier (PLCC).
© 1996 National Semiconductor Corporation
Printed in the U.S.A.
■
■
Applications
■
■
■
■
■
■
■
CCD imaging
IR imaging
FLIR processing
Medical imaging
High definition video
Instrumentation
Radar processing
Digital communications
SFDR (dBc)
SNR (dB), SFDR (dBc)
Note that the reason for this degradation is the reduced ability of
the CLC949 to handle high slew rates at high temperatures. In
applications such as CCD imaging systems, where the slew rate at
the A/D sampling instant is very low, this degradation will not be
nearly so pronounced.
■
Power Dissipation vs. Conversion Rate
200
150
Power (mW)
The CLC949 exhibits very stable performance over the commercial
and industrial temperature ranges. Most parameters shift very
little as the ambient temperature changes from -40°C to 85°C. An
exception to this rule is the dynamic performance of the converter.
As the temperature is increased, the distortion increases,
especially at higher input frequencies. This can be seen in the plot
on page 3. For input frequencies below 7MHz, there is relatively
little variation in distortion as the temperature is changed, but at
higher input frequencies, it is apparent that the performance
degrades as the temperature is increased.
■
Very low/programmable power
0.07W @ 5MSPS
0.22W @ 20MSPS
0.40W @ 30MSPS
Single supply operation (+5V)
0.5 LSB differential linearity error
Wide dynamic range
72dBc spurious-free dynamic range
68dB signal-to-noise ratio
No missing codes
Comlinear CLC949
Very Low-Power, 12-Bit, 20MSPS Monolithic Converter
August 1996
100
50
0
0
5
10
15
20
Sample Rate (MSPS)
http://www.national.com
CLC949 Electrical Characteristics (+VDD = + 5V, Medium Bias (200µA): unless specified)
PARAMETERS
Case Temperature
CONDITIONS
DYNAMIC CHARACTERISTICS
overvoltage recovery VIN = 1.5FS
effective aperture delay
aperture jitter
slew rate
settling time
NOISE and DISTORTION (20MSPS)
Signal-to-Noise Ratio (no harmonics)
4.985MHz;
FS
9.663MHz;
FS
Spurious-Free Dynamic Range
4.985MHz;
FS -1dB
9.663MHz;
FS -1dB
Intermodulation Distortion
f1 = 5.58MHz @ FS -7dB; f2 = 5.70MHz @ FS -7dB
3dB bandwidth (full power)
TYP
MIN/MAX RATINGS
+25˚C
0 to 70˚C -40 to 85˚C
UNITS
SYMBOL
15
3.0
7.0
400
12
25
6.2
15
25
6.2
15
25
6.2
15
ns
ns
ps(rms)
V/µS
ns
OR
TA
AJ
SR
ST
68
68
66
66
66
66
66
66
dB
dB
SNR2
SNR3
72
72
63
58
55
dBc
dBc
SFDR2
SFDR3
dBc
MHz
IMD
BW
-70
100
NOISE and DISTORTION (5MSPS, low bias)
Signal-to-Noise Ratio (no harmonics)
2.4MHz;
FS
Spurious-Free Dynamic Range
2.4MHz;
FS -1dB
70
68
68
67
dB
SNR1
78
66
66
64
dBc
SFDR1
NOISE and DISTORTION (25.6MSPS, high bias)
Signal-to-Noise Ratio (no harmonics)
9.894MHz;
FS
Spurious-Free Dynamic Range
9.894MHz;
FS-1dB
67
63
63
63
dB
SNR4
67
59
53
48
dBc
SFDR4
0.5
1.2
60
0
5.0
15
1.0
1.0
3.5
1.0
3.5
1.0
3.5
0
25
0
25
0
25
5.0
5.0
5.0
LSB
LSB
dB
codes
mV
µV/°C
%FS
DNL
INL
CMRR
MC
VIO
DVIO
GE
dB
dB
PSRA
PSRD
3.24-3.26
1.24-1.26
1.98-2.02
V
V
V
VREFP
VREFN
VDIFF
VCM
VDM
IBN
CIN
DC ACCURACY and PERFORMANCE
differential non-linearity
integral non-linearity
common mode rejection ratio
missing codes
mid-scale offset
temperature coefficient
gain error
power supply rejection
Vdda
Vddd
dc; FS
dc; FS
dc
dc
dc
55
50
VOLTAGE REFERENCE CHARACTERISTICS
positive reference voltage (internal)
negative reference voltage (internal)
differential reference voltage (Vrefp - Vrefn)
3.25
1.25
2.0
ANALOG INPUT PERFORMANCE
common mode range
differential range
analog input bias current
analog input capacitance
2-3
±2
±0.1
5.0
±1.0
10
±1.0
10
±1.0
10
V
V
µA
pF
logic LOW
logic HIGH
logic LOW
logic HIGH
±0.1
±0.1
1
4.0
±1.0
±1.0
1
4.0
±1.0
±1.0
1
4.0
±1.0
±1.0
V
V
µA
µA
VIL
VIH
IIL
IIH
logic LOW
logic HIGH
0.25
4.8
0.5
4.5
0.5
4.5
0.5
4.5
V
V
VOL
VOH
30
10
7.0
6.5
30
10
4.5
6.5
30
10
4.5
6.5
30
10
4.5
6.5
MSPS
KSPS
ns
clocks
CR
CRM
THLD
44
220
65
400
60
300
60
300
60
300
mA
mW
mW
mW
IDD
PDM
PDL
PDH
DIGITAL INPUTS
CMOS input voltage
CMOS input current
DIGITAL OUTPUTS
CMOS output voltage
TIMING
maximum conversion rate
minimum conversion rate
data hold time
pipeline delay
POWER REQUIREMENTS
supply current (+Vdd)
power dissipation
power dissipation (low bias)
power dissipation (high bias)
20MSPS
5MSPS
30MSPS
3.24-3.26
1.24-1.26
1.98-2.02
3.24-3.26
1.24-1.26
1.98-2.02
Min/max ratings are based on product characterization and simulation. Individual parameters are tested as noted. Outgoing quality levels
are determined from tested parameters.
http://www.national.com
2
CLC949 Typical Performance Characteristics (+VDD = + 5V, Med Bias, Fs = 20MSPS: unless specified)
Output Spectrum 9MHz
-20
-20
-20
-40
-60
-80
Output Level (dBFS)
0
-40
-60
-80
-100
-100
0
2
6
4
8
2
8
10
0
SNR
40
20
60
SFDR
SNR
40
20
-20
0
-10
SFDR
SNR
40
20
-40
-20
-30
0
-10
-50
10
Medium Bias
70
SFDR (dBc)
SNR (dB)
High Bias
SNR (dB)
Low Bias
50
40
50
Medium Bias
Low Bias
60
50
Fin = 5MHz
FS = 20MHz
Fin = 5MHz
30
0
40
0.1
100M
1.0
100
10
0.1
1.0
Sample Rate (MSPS)
Input Frequency (MHz)
Two Tone Intermodulation Distortion
100
10
Sample Rate (MSPS)
Integral Non-Linearity
0
10
High Bias
60
60
0
-10
80
SFDR (dBc)
70
10M
-20
-30
SFDR vs. Sample Rate vs. Bias
70
1M
-40
Input Amplitude (dBFS)
SNR vs. Sample Rate vs. Bias
SNR & SFDR vs. Input Frequency
100k
60
Input Amplitude (dBFS)
Input Amplitude (dBFS)
80
10
0
-50
10
8
SNR & SFDR vs. Input Amplitude 9MHz
0
0
6
4
80
SNR (dB) & SFDR (dBc)
SFDR
-30
2
Frequency (MHz)
80
SNR (dB) & SFDR (dBc)
SNR (dB) & SFDR (dBc)
6
4
SNR & SFDR vs. Input Amplitude 5MHz
SNR & SFDR vs. Input Amplitude 1MHz
-40
-80
Frequency (MHz)
80
-50
-60
-120
0
10
Frequency (MHz)
60
-40
-100
-120
-120
SNR (dB), SFDR (dBc)
Output Spectrum 15MHz
0
Output Level (dBFS)
Output Level (dBFS)
Output Spectrum 1MHz
0
Differential Non-Linearity
2.5
1.5
1
1.5
-60
-80
1
DNL (LSBs)
-40
INL (LSBs)
Output Level (dBFS)
2
-20
0.5
0
-0.5
-1
-1.5
-100
0.5
0
-0.5
-1
-2
-2.5
-120
0
2
6
4
8
-1.5
0
10
Frequency (MHz)
1000
2000
3000
4000
0
3000
2000
4000
Output Code
SFDR vs. Input Frequency
Pulse Settling Response
4000
I/O Timing (Convert CLK & Bit Skew)
)
80
76
2000
1000
(
-20°C
300
0°C
72
20°C
200
68
60°C
100
80°C
60
0
50
100
Time (ns)
150
200
Output Data
Convert
40°C
64
0
400
p
3000
SFDR (dBc)
ADC Output Code
1000
Output Code
0
1
10
Input Frequency (MHz)
3
100
0
4
8
12
16
20
Time (ns)
http://www.national.com
Recommended Operating Conditions
supply voltage (VDD)
differential voltage between any two GND’s
analog input voltage range (full scale)
digital input voltage range
operating temperature range
clock pulse-width high (Cpwh)
Absolute Maximum Ratings*
-0.5V to +7V
supply voltage (VDD)
differential voltage between any two GND’s
200mV
analog input voltage range
-0.5V to +VDD
digital input voltage range
-0.5V to +VDD
output short circuit duration (one pin to gnd)
infinite
junction temperature
+175°C
storage temperature range
-65°C to +150°C
lead solder duration (+300°C)
10 sec
+5V ± 5%
<10mV
1.25 – 3.25V
0 to VDD
0°C to 70°C
> 25ns
*NOTE: Absolute maximum ratings are limiting values, to be applied individually, and beyond which the serviceability of the circuit may be impaired.
Functional operability under any of these conditions is not necessarily implied. Exposure to maximum ratings for extended periods may affect device
reliability.
will all be tied together. For more detailed discussion,
please refer to the paragraph on power and grounds in
the applications section of the databook.
BC1
CLK
NC
VDDD
VDDD
VDDD
VDDA
VDDA
VDDA
VREFPO
VREFNO
Pinout & Pin Description and Usage
6 5 4 3 2 1 44 43 42 41 40
VREFMO 7
39 BCO
38 D12(LSB)
TOP VIEW
VREFP 8
VREFN 9
Clock (CLK)
The CLK accepts a CMOS clock input. Samples are
taken on the falling edges of the CLK and data emerges
6 1/2 clock cycles later, on to the rising edge of the CLK.
37 D11
36 D10
VREFPC 10
VREFNC 11
35 D9
44-Pin PLCC
NC 12
34 D8
BIASC 13
33 D7
32 D6
GNDA 14
VINP 15
Output Data (D1-D12, MSBINV, OE\)
The data emerges from the CLC949 as CMOS level
digital data on D1(MSB) through D12(LSB). The
outputs can be put into a high impedance state by
bringing OE\ high. There is an internal pulldown
resistor so that if this input is left open, the output data is
enabled. MSBINV will invert the MSB of the output data.
With MSBINV in the high state, the output data is two’s
complement, when low, the output data format is offset
binary. An internal pulldown resistor makes the output
default to offset binary if MSBINV is left open.
31 D5
30 D4
VINN 16
GNDA 17
29 D3
D2
D1(MSB)
OE\
MSBINV
GNDD
GNDD
GNDD
GNDA
GNDA
GNDA
GNDA
18 19 20 21 22 23 24 25 26 27 28
References (VREFN, VREFP, VREFNO, VREFPO, VREFNC,
VREFPC, VREFMO)
To use the internal references, connect VREFPO to VREFP
and VREFNO to VREFN. The nominal value for VREFPO is
3.25V and for VREFNO is 1.25V. VREFPC and VREFNC are
internal reference points which should be bypassed to
GND with a 0.1µF capacitor.
VREFMO is an output
voltage that is equal to the mid point of the reference
range and can be used to apply the appropriate offset to
the analog inputs. For a more detailed discussion on
references, see the paragraph on references in the
applications section of this datasheet.
Bias Control (BCO, BC1, BIASC)
The DC bias current of the CLC949 is controlled by three
pins: BCO, BC1, and BIASC. BC0 and BC1 are digital
CMOS inputs and set the bias current in accordance with
the truth table below:
Analog Input (VINP, VINN)
The analog input to the CLC949 is a differential signal
applied to VINP and VINN. For more detail on driving the
inputs, see the paragraphs in the applications section of
this datasheet.
Power Supplies and Grounds (VDDA, VDDD, GNDA, GNDD)
The power and ground pins of the CLC949 are split into
those that supply the analog portions of the integrated
circuit (VDDA, GNDA) and the digital portions of the chip
(VDDD, GNDD). If your system uses separate power and
ground planes, then performance can be improved by
making use of the appropriate pins. In many systems,
the power pins will all be tied together and the GND pins
http://www.national.com
BC0
BC1
Bias Current
PD@10MSPS
0
0
Default: Med Bias (200µA)
200mW
1
0
Analog Mode
Variable
0
1
High Bias (400µA)
350mW
1
1
Low Bias (50µA)
75mW
In the analog mode, the user provides a bias current
through the BIASC pin of the CLC949. As the bias
current is increased, the power dissipation of the CLC949
is increased and the part becomes capable of increased
conversion rates.
NC
No connection - leave these pins open.
4
CLC949 OPERATION
Application
In a high speed data acquisition system, the overall
performance is often determined by the A/D converter
and its surrounding circuitry. You should pay special
attention to the data converter and its support circuitry if
you want to obtain the best possible performance. The
information on these pages is intended to help you
design the circuitry surrounding the CLC949 in such
a way as to achieve superior results. Additional
information is available in the form of Comlinear
applications notes. Especially useful are AD-01 and
AD-02.
Sinusoisal
Clock Input
1k
Sample
-3 Valid
Sample
-2 Valid
Sample
-1 Valid
10k
50Ω
4
2.2k
1
0.1µF
5
To CLC949
Clock
74AC04
10k
0.1µF
Driving the Differential Input
The CLC949 has a differential input with a common
mode voltage of 2.25V. Since not all applications have a
signal preconditioned in this manner there is often a need
to do a single-ended-to-differential conversion and to add
offset. In systems which do not need to be DC coupled,
the best method for doing this is with an RF transformer
such as the Minicircuits TMO1-1T. This is an RF
transformer with a center tapped secondary which will
operate over a frequency range of 50kHz to 200MHz.
You can offset the input and split the phases simply by
connecting the center tap to the mid scale reference
output (VREFMO) as shown in Figure 3.
Sample 5
CLK
Output
Data
8
In addition to the circuitry generating the clock, the
layout of the clock distribution network can affect the
overall performance of the converter. To obtain the best
possible performance, a clock driver with very low output
impedance and fast edge rates such as the 74AC04,
should be placed as close as possible to the CLC949
clock input pin. Additional length in the circuit trace for
the clock will cause an increase in the jitter seen by the
converter. On the CLC949 evaluation board, the
E949PCASM, there is less than 1/16th of an inch
between the 74AC04 that is driving the clock input and
the input to the CLC949. If the system has several
CLC949s, and jitter is liable to generate problems, then
use a separate clock driver for each CLC949. Each
driver should be placed as close to the converter that it is
driving as is practicable.
Sample 7
Sample 3
3
Here the CLC006 cable driver is used as a comparator to
generate a high speed clock. The CLC006 has less than
2ps of jitter and has rise and fall times less than 1ns. The
CLC006 output is then buffered by a 74AC04 which
maintains fast edge rates and provides CMOS levels for
the CLC949. If there is excessive jitter in the CLK, then
the digitized signal will exhibit an excessive amount of
noise, especially for high frequency inputs. For a more
detailed description of this phenomenon, please read the
Comlinear Application Note AD-03.
Sample 6
Sample 1
6
50Ω
+
Figure 2: Clock Generation
Effective Aperture Delay
Sample 2 Sample 4
9
10k
CLC006
1k
Timing and CLK Generation
The falling edge of the CLK pulse causes the input sample-and-hold amplifier to transition into the hold mode.
The sample is taken approximately 3ns after this falling
edge. The digitized data is presented to the output latches 6 1/2 clock cycles later and is held until after the next
rising edge of CLK. This timing is shown in the timing
diagram, Figure 1.
Sample 0
0.1µF
+5V
Circuit Description
The CLC949 ADC consists of an input Sample-and-Hold
Amplifier (SHA) followed by a pipelined quantizer.
Internal reference sources and output data latches
complete the major functions required of an A/D
converter. Digital error correction in the quantizer helps
to provide accurate conversions of high speed dynamic
signals. The speed of the analog circuitry is determined
in part by the internal bias currents applied. The CLC949
allows you to make this important tradeoff between
power and performance through settings on two digital
control pins and for fine adjustments through the use of
an external resistor.
Analog
Input
+5V
+5V
2.2k
Sample
0 Valid
Output Hold Time
Figure 1: Timing Diagram
The CLC949 is designed to operate with a CMOS clock
signal. To obtain the lowest possible noise when
digitizing a high frequency input, more care must be
taken in the generation of this clock than is usually
accorded to CMOS Clocks. To minimize aperture jitter
induced errors, the CLK needs to have as low a
jitter as possible and as fast an edge rate as possible. To
obtain a very low jitter clock from a sinusoidal source, the
circuit shown in Figure 2 is recommended.
This set up can be realized on the CLC949 evaluation
board by enabling option 1. See E949PCASM data
sheet for details. A transformer coupled input will allow
the CLC949 to exhibit the best possible distortion
performance for high frequency input signals.
5
http://www.national.com
VIN
Reference Generation
The CLC949 has internally generated reference
voltages. To use these references, you must externally
connect the reference inputs by shorting VREFPO to
VREFP and VREFNO to VREFN. During the conversion
cycle, the impedance on these four pins varies
dynamically. To maintain stable biases on these pins you
must bypass them with 0.1µF to GND. If you want to provide an external reference, then you have to be careful
to provide low output impedance drivers to the VREFP and
VREFN pins. Bypass capacitors on all reference pins are
recommended for best performance.
VINP
15pF
CLC949
VREFMO
50Ω
VINN
TM01-1T
15pF
Figure 3: Transformer Coupled Input
Since the transformer response does not extend to DC it
is not an effective solution for applications which require
DC coupled inputs.
To drive the input of the CLC949, and retain DC
information, an amplifier configuration is required.
Comlinear suggests the use of the circuit shown in Figure 4.
This circuit is used on the E949PCASM.
Bias Control
One of the unique features of the CLC949 is that it allows
you to set the internal bias current of the device. When
designing an A/D converter a tradeoff is made between
the amount of power dissipated and the
performance. The CLC949 allows you to make this
tradeoff yourself. The bias current is controlled by the
pins BC0 and BC1. These two pins are digital input pins
from which one of three discrete bias points may be
selected (see truth table on page 4 of this datasheet) or
an external bias may be provided through the analog bias
control pin BIASC. If BC0 and BC1 are left open, they
will drift low and provide the default bias condition which
results in 220mW of dissipation at 20MHz sampling rate.
The actual power dissipated by the device is a function
of both the bias condition and the sample rate. The
relationship between power and speed is shown for the
three discrete bias points in Figure 5.
1k
CLC428
+
U5A
1.25k
1k
+5V
CLC428
+
U5B
500Ω
500Ω
500Ω
VIN
R29
400Ω
+5V
R3
400Ω
CLC409
R30
+
50Ω
R7
400Ω
R10
50Ω
+5V
U7
R8
50Ω
+
R2
400Ω
CLC409
-
U6
VREFMO
R27
50Ω
VINP
15pF
CLC949
R26
50Ω
Power Dissipation vs. Sample Rate
VINN
15pF
Power Dissipation (mW)
400Ω
Figure 4: Amplifier Coupled Input
In this circuit U7 buffers the analog input with a gain of
+1, and U6 buffers the input with a gain of -1. The
circuit has been designed so that U6 and U7 have the
same loop gain, thereby offering the best possible match
of their AC characteristics. U5 is used to generate the
required offset voltages which are summed into the input
signal via U6 and U7. The CLC409 was selected for U6
and U7 due to its current feedback topology which allows
for very low distortion even at high frequencies, and its
excellent phase linearity. Phase match between U6 and
U7 is critical for good pulse response. To generate the
D.C. offsets, the CLC428 dual Op-amp was selected.
The CLC428 is a voltage-feedback op amp with very
good DC characteristics, and the large bandwidth makes
the output impedance low over a wide range of frequencies, allowing good AC performance.
High Bias
300
200
Medium Bias
100
Low Bias
0
100k
1M
10M
40M
Sample Rate (Hz)
Figure 5: Power Dissipation vs. Sample Rate
As the bias is turned up, the ability of the CLC949 to
handle high frequency inputs and the power dissipation
of the CLC949 increases. To use the BIASC pin, attach
a resistor from the pin to VDDA. The current drawn by this
resistor is mirrored in the device to set the internal bias
currents. A smaller value resistor will result in higher bias
currents and higher performance.Beyond a certain
point, additional improvement is not seen, although
power continues to increase. For this reason, it is
recommended that bias setting resistors of less than
10K not be used. To generate the graph in Figure 6 a
CLC949 was set to sample a signal 1dB below full scale
Regardless of how the input is driven, a small capacitor
(15pF) should be added from the VINP and VINN
terminals to GND. This will help to reduce the current
transients that are generated by the CLC949 inputs
during sampling.
http://www.national.com
400
6
with a frequency of 1/2 the sample rate. The bias current
was then turned up until the SNR was better than 65dB
and the SFDR exceeded 72dB. The axis on the left
shows the power that was dissipated by the device as a
function of speed, whereas the other curve uses the axis
on the right to show the resistor value required to obtain
this bias.
the McKenzie #PLCC-44P-T-SMT socket which has low
parasitic impedances. The traces from the clock source
to the CLC949 should be as short as possible, if forced
to put the clock driver more than a couple of
centimeters away from the CLC949, then add a buffer for
the clock right next to the CLC949.
There is an evaluation board available for the CLC949
(E949PCASM) This board can be used to quickly
evaluate the performance of the CLC949 data converter.
Use of this evaluation board as a model for your PCB layout is recommended. The schematic for this evaluation
board is shown in Figure 8 on the following page. The
board layout for the E949PCASM is shown in the
E949PCASM datasheet.
Power Dissipation & Programming
Resistor vs. Sample Rate
200
50
40
Resistor
100
30
Rp (kΩ)
Power (mW)
150
Power
50
Power Supplies, Grounding and Bypassing
To obtain the best possible performance from high speed
devices, you must pay close attention to power supplies,
bypassing and grounding. This applies not only to the
A/D converter itself but to the entire system.
20
0
0
0
5
15
10
20
Sample Rate (MSPS)
The recommended supply decoupling scheme for the
CLC949 includes:
Figure 6: Power Dissipation & Programming
Resistor vs. Sample Rate
• One 0.01 to 0.033µF capacitor between each
power pin and GND.
Dynamic Power Down
In systems where you do not use the A/D converter continually, and low power consumption is a key requirement, the power to the CLC949 can be turned down while
it is not being used. This is done through the use of the
BIASC pin, and a programming resistor to the power
supply. When the potential on this resistor is brought low,
the part goes into a sleep mode which saves power. This
can be accomplished by connecting the bias setting
resistor to a CMOS gate as shown in Figure 7. In sleep
mode the CLC949 will draw approximately 8mA, or
40mW on a 5V supply.
• One 6.8 to 10µF capacitor per board, placed no
more than a few inches from the A/D connected
between VDD and GND.
• One 0.1µF capacitor from each of the reference
inputs (VREFP, VREFN, VREFPC, VREFNC) to GND.
• If the board has supplies that include excessive
digital switching noise, then ferrite beads in series
with the power feed to the A/D should also be
included.
• Proper bypassing of all other integrated circuits
on the board, especially digital logic I.C.s.
Package Thermal Resistance
CLC949
Package
BIASC BC0 BC1
44-pin PLCC
Sleep
Rp* 10k
CMOS Inverter
qJC
qJA
10°C/W
35°C/W
Ordering Information
VDD
*See Figure 6 above.
Model
CLC949ACQ
CLC949AJQ
Figure 7: Dynamic Power Savings
PCB Layout
The keys to a successful CLC949 layout are
a substantial low-impedance ground plane, short
connections in and out of the data converter, and proper
power supply decoupling. The use of a socket for the
final design is not recommended but if one must be used
during debug or prototyping, then Comlinear recommends
Temperature Range
Description
0˚C to +70˚C
-40˚C to +85˚C
44-pin PLCC
44-pin PLCC
Power Requirements
Vcc = +5V, 5MSPS, Low Bias
Vcc = +5V, 20MSPS, Med Bias
Vcc = +5V, 30MSPS, High Bias
7
Typ
Units
65
220
400
mW
mW
mW
http://www.national.com
Figure 8: CLC949 Evaluation Board
VDDD
VDDD
VDDA
VDDA
VDDA
VREFNO
VREFPO
BCO
D12(LSB)
D9
GNDA
VREFNC
GNDA
D10
GNDD
VREFPC
GNDD
D11
GNDD
VREFN
VREFMO
VREFP
NC
OE\
CLK
CLC949 Eval Board
VDDD
MSBINV
BC1
8
GNDA
VINN
VINP
D3
D4
D5
D6
D8
D7
GNDA
GNDA
NC
D1(MSB)
BIASC
GNDA
D2
http://www.national.com
Data Ready
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
This page intentionally left blank.
9
http://www.national.com
This page intentionally left blank.
http://www.national.com
10
This page intentionally left blank.
11
http://www.national.com
Comlinear CLC949
Very Low-Power, 12-Bit, 20MSPS Monolithic Converter
Customer Design Applications Support
National Semiconductor is committed to design excellence. For sales, literature and technical support, call the
National Semiconductor Customer Response Group at 1-800-272-9959 or fax 1-800-737-7018.
Life Support Policy
National’s products are not authorized for use as critical components in life support devices or systems without the express written approval
of the president of National Semiconductor Corporation. As used herein:
1. Life support devices or systems are devices or systems which, a) are intended for surgical implant into the body, or b) support or
sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to
cause the failure of the life support device or system, or to affect its safety or effectiveness.
N
National Semiconductor
Corporation
National Semiconductor
Europe
National Semiconductor
Hong Kong Ltd.
National Semiconductor
Japan Ltd.
1111 West Bardin Road
Arlington, TX 76017
Tel: 1(800) 272-9959
Fax: 1(800) 737-7018
Fax: (+49) 0-180-530 85 86
E-mail: europe.support.nsc.com
Deutsch Tel: (+49) 0-180-530 85 85
English Tel: (+49) 0-180-532 78 32
Francais Tel: (+49) 0-180-532 93 58
Italiano Tel: (+49) 0-180-534 16 80
13th Floor, Straight Block
Ocean Centre, 5 Canton Road
Tsimshatsui, Kowloon
Hong Kong
Tel: (852) 2737-1600
Fax: (852) 2736-9960
Tel: 81-043-299-2309
Fax: 81-043-299-2408
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said
circuitry and specifications.
http://www.national.com
12
Lit #150949-004
Similar pages