NSC ADC16471

ADC16071/ADC16471
16-Bit Delta-Sigma 192 ks/s Analog-to-Digital Converters
General Description
Key Specifications
The ADC16071/ADC16471 are 16-bit delta-sigma analogto-digital converters using 64 c oversampling at
12.288 MHz. A 5th-order comb filter and a 246 tap FIR decimation filter are used to achieve an output data rate of up to
192 kHz. The combination of oversampling and internal digital filtering greatly reduces the external anti-alias filter requirements to a simple RC low pass filter. The FIR filters
offer linear phase response, 0.005 dB passband ripple, and
t 90 dB stopband rejection. The ADC16071/ADC16471’s
analog fourth-order modulator uses switched capacitor
technology. A built-in fully-differential bandgap voltage reference is also included in the ADC16471. The ADC16071
has no internal reference and requires externally applied
reference voltages.
The ADC16071/ADC16471 use an advanced BiCMOS process for a low power consumption of 500 mW (max) while
operating from a single 5V supply. A power-down mode reduces the power supply current from 100 mA (max) in the
active mode to 1.3 mA (max).
The ADC16071/ADC16471 are ideal analog-to-digital front
ends for signal processing applications. They provide a
complete high resolution signal acquisition system that requires a minimal external anti-aliasing filter, reference, or
interface logic.
The ADC16071/ADC16471’s serial interface is compatible
with the DSP56001, TMS320, and ADSP2100 digital signal
processors.
Y
Y
Y
Y
16 bits
b 94 dB (typ)
b 80 dB (typ)
192 kHz (min)
500 mW (max)
275 mW (max)
6.5 mW (max)
Key Features
Y
Y
Y
Y
Y
Y
Y
Y
Voltage reference (ADC16471 only)
Fourth-order modulator
64 c oversampling with a 12.288 MHz sample rate
Adjustable output data rate from 7 kHz to 192 kHz
Linear-phase digital anti-aliasing filter:
Ð 0.005 dB passband ripple
Ð 90 dB stopband rejection
Single a 5V supply
Power-down mode
Serial data interface compatible with popular
DSP devices
Applications
Y
Y
Y
Y
Y
Y
Connection Diagram
Resolution
Total harmonic distortion
48 kHz output data rate
192 kHz output data rate
Maximum output data rate
Power dissipation
Ð Active
192 kHz output data rate
48 kHz output data rate
Ð Power-down
Medical instrumentation
Process control systems
Test equipment
High sample-rate audio
Digital Signal Processing (DSP) analog front-end
Vibration and noise analysis
Ordering Information
Part No.
Package
NS Package
No.
ADC16471CIN
ADC16471CIWM
ADC16071CIN
ADC16071CIWM
24-Pin Molded DIP
24-Pin SOIC
24-Pin Molded DIP
24-Pin SOIC
N24C
M24B
N24C
M24B
TL/H/11454 – 2
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
C1995 National Semiconductor Corporation
TL/H/11454
RRD-B30M75/Printed in U. S. A.
ADC16071/ADC16471 16-Bit Delta-Sigma 192 ks/s Analog-to-Digital Converters
February 1995
Block Diagram
ADC16471
TL/H/11454 – 1
ADC16071
TL/H/11454 – 22
2
Absolute Maximum Ratings (Notes 1 and 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
ESD Susceptibility (Note 5)
Human Body Model
Machine Model
Supply Voltage (VA a , VD a , and VM a )
See AN-450 ‘‘Surface Mounting Methods and Their Effect
on Product Reliability’’ for other methods of soldering surface mount devices.
Logic Control Inputs
Voltage at Other
Inputs and Outputs
a 6.5V
b 0.3V to VD a a 0.3V
b 0.3V to VA a e VM a a 0.3V
g 25 mA
Input Current at Any Pin (Note 3)
g 100 mA
Package Input Current (Note 3)
Maximum Junction Temperature (Note 4)
150§ C
b 65§ C to a 150§ C
Storage Temperature
Lead Temperature
N Package (Soldering, 10 sec.)
300§ C
WM Package (Infrared, 15 sec.)
220§ C
WM Package (Vapor Phase, 60 sec.)
215§ C
4000V
250V
Operating Ratings (Notes 1 and 2)
Temperature Range
(Tmin s TA s Tmax)
ADC16471CIN, ADC16071CIN, b40§ C s TA s a 85§ C
ADC16471CIWM, ADC16071CIWM
Supply Voltage
VA a , VD a , VM a
4.75V to 5.25V
Converter Electrical Characteristics
The following specifications apply for VM a e VA a e VD a e 5.0VDC, VMID e VA a /2 e 2.50V, VREF a e VMID a 1.25V,
VREFb e VMID b 1.25V, fCLK e 24.576 MHz, and dynamic tests are performed with an input signal magnitude set at b6 dB
with respect to a full-scale input unless otherwise specified. Boldface limits apply for TA e TJ e Tmin to Tmax; all other
limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Resolution
Limits
(Note 7)
Units
(Limit)
16
Bits
72
dB (min)
fCLK e 24.576 MHz (fs e 192 kHz)
S/(N a D)
Signal-to-Noise a Distortion Ratio
Measurement bandwidth e 0.45fs
fIN e 19 kHz
THD
Total Harmonic Distortion
fIN e 19 kHz
0.010
0.022
% (max)
IMD
Intermodulation Distortion
f1 e 18.5 kHz, f2 e 19.5 kHz
0.010
0.017
% (max)
Converter Noise Floor (Note 8)
Measurement Bandwidth e 0.45fs
b 88
b 77
dBFS (min)
85
80
73
dB (min)
dB (min)
76
fCLK e 6.144 MHz (fs e 48 kHz)
S/(N a D)
Signal-to-Noise a Distortion Ratio
Measurement bandwidth e 0.45fs
fIN e 5 kHz
THD
Total Harmonic Distortion
fIN e 5 kHz
0.002
0.0055
0.008
% (max)
% (max)
IMD
Intermodulation Distortion
f1 e 4 kHz, f2 e 5.5 kHz
0.003
0.009
0.01
% (max)
% (max)
Converter Noise Floor (Note 8)
Measurement Bandwidth e 0.45fs
b 99
b 92
b 89
dBFS (min)
dBFS (min)
g 1.0
%FS (max)
OTHER CONVERTER CHARACTERISTICS
ZIN
Input Impedance (Note 9)
DAV
Gain Error
34
VOS
Input Offset Voltage
IA
Analog Power Supply Current
23
31
mA (max)
IM
Modulator Power Supply Current
fCLK e 24.576 MHz
fCLK e 6.144 MHz
1.6
0.4
2.4
0.8
mA (max)
ID
Digital Power Supply Current
fCLK e 24.576 MHz
fCLK e 6.144 MHz
50
13
65
23
mA (max)
ISPD
Power-Down Supply Current
IA a ID a IM
0.25
1.3
mA
PD
Power Dissipation
0.375
0.5
W
g 0.2
kX
15
VMID
VA a /2
3
mV
V
Digital Filter Characteristics
The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified. Boldface limits apply for
TA e TJ e Tmin to Tmax; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Note 7)
Units
(Limit)
Stopband Rejection
b 90.0
dB
Passband Ripple
g 0.005
dB
3 dB Cutoff Frequency
0.45
fs
Data Latency
3,968
Clock Cycles
Reference Characteristics (ADC16471 Only)
The following specifications apply for VA a e VD a e VM a e 5V, unless otherwise specified. Boldface limits apply for TA
e TJ e Tmin to Tmax; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Note 7)
Units
(Limit)
VREF a
Positive Internal Reference
Output Voltage
VMID a 1.25
VMID a 1.175
VMID a 1.325
V (min)
V (max)
VREFb
Negative Internal Reference
Output Voltage
VMID b 1.25
VMID b 1.325
VMID b 1.175
V (min)
V (max)
D(VREF a –
VREFb)/DT
Internal Reference
Temperature Coefficient
DVREF a /DI
Positive Internal Reference
Load Regulation
Sourcing (0 mA s I s a 10 mA)
Sinking (b1 mA s I s 0 mA)
3.4
6.0
DVREFb/DI
Negative Internal Reference
Load Regulation
Sinking (b1 mA s I s 0 mA)
Sourcing (0 mA s I s 10 mA)
3.2
6.0
Typical
(Note 6)
Limits
(Note 7)
30
ppm/§ C
mV (max)
Input Reference Characteristics (ADC16071 Only)
The following specifications apply for VA a e VD a e VM a e 5V.
Symbol
Parameter
Conditions
Units
VREF a
Positive Reference Voltage
1
VA a
V
V
VREFb
Negative Reference Voltage
0
VA a b 1
V
V
VREF a – VREFb
Total Reference Voltage
1
VA a
V
V
4
DC Electrical Characteristics
The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified. Boldface limits apply for TA
e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Typical
(Note 6)
Conditions
VIH
Logic High Input Voltage
VD a e 5.25V
VIL
Logic Low Input Voltage
VD a e 4.75V
Limits
(Note 7)
Units
(Limit)
VD a
2.3
V (max)
V (min)
0.8
b 0.3
V (max)
V (min)
VOH
Logic High Output Voltage
Logic High Output Current e b400 mA,
VD a e 4.75V
2.4
V (min)
VOL
Logic Low Output Voltage
Logic Low Output Current e 2 mA,
VD a e 5.25V
0.5
V (max)
IIN(1)
Logical ‘‘1’’ Input Current
1.0
5.0
mA (max)
IIN(0)
Logical ‘‘0’’ Input Current
b 1.0
b 5.0
mA (max)
ITSI
SDO TRI-STATEÉ Leakage Current
VIN e 0.4V to 2.4V
1.0
5.0
mA (max)
CIN
Logic Input Capacitance
VIN e 0 to VD a
5
pF
AC Electrical Characteristics for Clock In (CLK), Serial Clock Out (SCO), and
Frame Sync In (FSI)
The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified. Boldface limits apply for TA
e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Note 7)
Units
(Limit)
25
1
MHz (max)
MHz (min)
1000
40
ns (max)
ns (min)
ns (min)
fCLK
CLK Frequency Range
(fCLK e 1/tCLK)
tCLK
CLK Period
(tCLK e 1/fCLK)
tCLKL
CLK Low Pulse Width
16
tCLKH
CLK High Pulse Width
14
ns (min)
tR
CLK Rise Time
10
3
ns (max)
ns (min)
tF
CLK Fall Time
10
3
ns (max)
ns (min)
tFSILOW
Minimum Frame Sync Input
Low Time before Frame Sync
Input Asserted High
2
tCLK (min)
tFSISU
Frame Sync Input Setup Time
10
ns (min)
tFSIH
Frame Sync Input Hold Time
10
ns (min)
tSCOD
Serial Clock Output Delay
Time from Rising Edge
of CLK
20
5
ns (max)
ns (min)
4
tCLK
tSCO
12
Serial Clock Output Period
5
AC Electrical Characteristics for Frame Sync Out (FSO), Serial Clock Out
(SCO), and Serial Data Out (SDO)
The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified. Boldface limits apply for TA
e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Note 7)
Units
(Limit)
tSCOFSOH
Delay from Serial Clock Out to
Frame Sync Output High
2
5
ns (max)
tSCOFSOL
Delay from Serial Clock Out to
Frame Sync Output Low
2
5
ns (max)
tSDOV
Delay from Serial Clock Out to
Serial Data Output Valid
3
8
ns (max)
tFSIFSOL
Delay from Frame Sync Input to
Frame Sync Output Low
8
tCLK (max)
AC Electrical Characteristics for Data Output Enable (DOE)
The following specifications apply for VA a e VD a e VM a e 5V unless otherwise specified. Boldface limits apply for TA
e TJ e TMIN to TMAX; all other limits TA e TJ e 25§ C.
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Note 7)
Units
(Limit)
tDOEE
Data Output Enable Delay Time
20
25
ns (max)
tDOED
Data Output Disable Delay Time
16
20
ns (max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: All voltages are measured with respect to GND, unless otherwise specified.
Note 3: When the input voltage (VIN) at any pin exceeds the power supply rails (VIN k GND or VIN l (VA a , VM a , or VD a )), the current at that pin should be limited
to 25 mA. The 100 mA maximum package input current rating allows the voltage at any four pins, with an input current of 25 mA each, to simultaneously exceed the
power supply voltages.
Note 4: The maximum power dissipation is a function of the maximum junction temperature (TJ(MAX)), total thermal resistance (iJA), and ambient temperature (TA).
The maximum allowable power dissipation at any ambient temperature is PD(max) e (TJ(max) b TA)/iJA. When board mounted, the ADC16071/ADC16471’s
typical thermal resistance is:
Order Number
iJA
ADC16071CIN, ADC16471CIN
47§ C/W
ADC16071CIWM, ADC16471CIWM
72§ C/W
Note 5: Human body model, 100 pF discharge through a 1.5 kX resistor. The machine model is a 200 pF capacitor discharged directly into each pin.
Note 6: Typicals are at TA e 25§ C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Output Quality Level).
Note 8: The VIN a pin is shorted to the VINb pin.
Note 9: The input impedance between VIN a and VINb due to the effective resistance of the switch capacitor input varies as follows:
1012
ZIN e
fCLK
2.35* (
)
2
6
Typical Performance Characteristics
S/(N a D) vs VIN Amplitude
S/(N a D) vs Output
Data Rate (fs)
S/(N a D) vs Temperature
Spectral Response,
fs e 192 kHz,
fIN e 20 kHz
Spectral Response,
fs e 192 kHz,
fIN e 80 kHz
Spectral Response,
fs e 48 kHz,
fIN e 5 kHz
Analog Supply Current
(IA a IM) vs Temperature
Digital Supply Current
ID vs Temperature
Analog Supply Current
(IA a IM) vs Output
Data Rate (fs)
Digital Supply Current
(ID) vs Output Data
Rate (fs)
Frequency Response of
Digital Filter
TL/H/11454 – 24
7
TL/H/11454 – 8
FIGURE 1. Timing Diagrams for Clock Input (CLK),
Frame Sync Input (FSI), and Serial Clock Output (SCO)
8
9
FIGURE 2. Detailed Timing Diagrams for Frame Sync Input (FSI), Frame Sync Out (FSO), Serial Clock Out (SCO), and Serial Data Out (SDO)
TL/H/11454 – 4
10
FIGURE 3. Timing Diagrams for Frame Sync Out (FSO), Serial Clock Out (SCO), and Serial Data Out (SDO)
TL/H/11454 – 5
11
FIGURE 4. Master/Slave Mode Timing Diagrams
TL/H/11454 – 6
TL/H/11454 – 7
FIGURE 5. Timing Diagrams for Data Output Enable (DOE) and Serial Data Out (SDO)
Pin Description
VM a
VREF a , VREFb These are the ADC16471’s internal differential reference’s bypass pins. Their nominal output voltage is g 1.25V centered
around the voltage at the VMID pin, typically
VA a /2. VREF a , VMID, and VREFb should
be bypassed with a parallel combination of
10 mF and 0.1 mF capacitors. For the
ADC16071, these are the reference voltage
inputs. VREF a and VMID should be bypassed with a parallel combination of 10 mF
and 0.1 mF capacitors.
VMID
This pin is the internal differential reference’s VA a /2 output pin. VMID should be
bypassed with a parallel combination of
10 mF and 0.1 mF capacitors.
VIN a , VINb
These are the ADC’s differential input pins.
Signals applied to these pins can be singleended or differential with respect to the
VMID voltage.
PD
This is the input pin used to activate the
power-down mode. When a logic LOW (0)
is applied to this pin the supply current
drops from 100 mA (max) to 1.3 mA (max).
AGND
This is the connection to system analog
ground. Internally, this ground is connected
to the analog circuitry, including the fourthorder modulator.
DGND
This is the connection to system digital
ground. Internally, this ground is connected
to all digital circuitry except the modulator’s
clock.
MGND
This is the ground pin for the modulator’s
clock. It should be connected to analog
ground through its own connection that is
separate from that used by AGND.
VA a
This pin is the connection to the system analog voltage supply. Best performance is
achieved when this pin is bypassed with a
parallel combination of 10 mF and 0.1 mF
capacitors.
VD a
This is the modulator’s supply pin. VM a should
be connected to the system analog voltage
supply with a circuit board trace or connection
that is separate from that used to supply VA a .
Best performance is achieved when this pin is
bypassed with a parallel combination of 10 mF
and 0.1 mF capacitors.
This pin is the connection to the system digital
voltage supply. Best performance is achieved
when this pin is bypassed with a parallel combination of 10 mF and 0.1 mF capacitors.
SFMT
This is the Serial Format pin. The logic level
applied to the SFMT pin determines whether
conversion data shifted out of the SDO pin is
valid on the rising or falling edge of SCO. It also
controls the format of the Frame Sync Out
(FSO) signal. See the Serial Interface section
for details.
TM0, TM1 Used to enabled test mode during production.
Connect both pins to DGND.
FSI
This is the Frame Sync Input pin. FSI is an
input used to synchronize the ADC16071/
ADC16471’s conversions to an external source.
The state of FSI is sampled on the falling edge
of CLK. See the Serial Interface section for
details.
CLK
This is the clock signal input pin. The signal applied to this pin sets the sample rate of the
ADC16071/ADC16471’s modulator to fCLK/2.
The frequency range can be 1 MHz s fCLK s
25 MHz.
SCO
This is the Serial Clock Output pin. The
ADC16071/ADC16471’s serial data transmission is synchronous with the SCO signal. SCO
has a frequency of fCLK/4. See the Serial Interface section for details.
SDO
This is the Serial Data Output pin. The
ADC16071/ADC16471’s conversion data is
shifted out from this pin synchronous to the
SCO signal. See the Serial Interface section
for details.
12
Pin Description (Continued)
Applications Information
FSO
TYPICAL PERFORMANCE RESULTS
Figure 6 shows a 16k point FFT plot of the baseband output
spectrum during conversion of a 24 kHz input signal.
TSI
DOE
This is the Frame Sync Output pin. FSO is used
to synchronize an external device to the
ADC16071/ADC16471’s 32 SCO cycle data
transmission frame. The format of the signal on
FSO depends on the logic level applied to the
SFMT pin. See the Serial Interface section for
details.
This is the Time Slot Input pin. TSI can be used
to allow two ADC16071/ADC16471’s to share a
single serial data line. The logic level applied to
TSI controls the active state of the ADC16071/
ADC16471’s DOE pin. See the Serial Interface
and the Two Channel Multiplexed Operation
sections for details.
This is the Data Output Enable pin. DOE is used
to control SDO’s TRI-STATE output buffer. The
active state of DOE is controlled by the logic level applied to the TSI pin. See the Serial Interface and the Two Channel Multiplexed Operation sections for details.
CLOCK GENERATION
The ADC16071/ADC16471 requires a sampling-clock signal that is free of ringing (over/undershoot of no more than
100 mVp-p) and has a rise and fall time in the range of 3 ns –
10 ns. We have tested and recommended crystal clock oscillators from Ecliptek (EC1100 series) and SaRonix
(NCH060 and NCH080 series). Both of these families use
HCMOS logic circuitry for very fast rise and fall times.
TL/H/11454 – 13
FIGURE 6. Typical Performance of the ADC16071/ADC16471 at fS e 192 kHz, fIN e 24 kHz
13
Applications Information (Continued)
Due to the data latency of the ADC16071/ADC16471’s digital filters, the first 31 conversions following a frame sync
input signal will represent inaccurate data, unless the frame
syncs are applied at constant 32 SCO cycle intervals. If no
FSI signal is applied (FSI is kept High or Low), the
ADC16071/ADC16471 will internally create a frame sync
every 32 SCO cycles.
The Data Output Enable pin (DOE), is used to enable and
disable the output of data on SDO. When DOE is deactivated, SDO stops driving the serial data line by entering a high
impedance TRI-STATE. DOE’s active state matches the
logic level applied to the Time Slot Input pin (TSI). If a logic
Low is applied to TSI, the ADC16071/ADC16471’s SDO pin
will shift out data when DOE is Low, and be in a high impedance TRI-STATE when DOE is High. If a logic High is applied to TSI, SDO will shift out data when DOE is High, and
be in a high impedance TRI-STATE when DOE is Low.
Overshoot and ringing can be reduced by adding a series
damping resistor between the crystal oscillator’s output (pin
8) and the ADC16071/ADC16471’s CLK (pin 12), as shown
in Figure 7. The actual resistor value is dependent on the
board layout and trace length that connects the oscillator or
CLK source to the ADC. A typical starting value is 50X with
a range of 27X to 150X.
TL/H/11454–23
FIGURE 7. Damping Resistor Reduces
Clock Signal Overshoot
SERIAL INTERFACE
The ADC16071 and the ADC16471 have three serial interface output pins: Serial Data Output (SDO), Frame Sync
Output (FSO), and Serial Clock Output (SCO). SCO has a
frequency of fCLK/4. Each of the ADC16071/ADC16471’s
16-bit conversions is transmitted within the first half of the
data transmission frame. A data transmission frame is 32
SCO cycles in duration. Two’s complement data shifts out
on the SDO pin beginning with bit 15 (MSB) and ending with
bit 0 (LSB), taking 16 SCO cycles. SDO then shifts out
zeroes for the next 16 SCO cycles to maintain compatibility
with two channel multiplexed operation.
The serial data that is shifted out of the SDO pin is synchronous with SCO. Depending on the logic level applied to the
Serial Format pin (SFMT), the data on the SDO pin is valid
on either the falling or rising edge of SCO. If a logic Low is
applied to SFMT, then the data on SDO is valid on the falling edge of SCO. If a logic High is applied to SFMT, then
the data on SDO is valid on the rising edge of SCO. See
Figure 2 .
The FSO signal is used to synchronize other devices to the
ADC16071/ADC16471’s data transmission frame. Depending on the logic level applied to SFMT, the signal on FSO is
either a short pulse (approximately one SCO cycle in duration) ending just before the transmission of bit 15 on SDO,
or a square wave with a period of 32 SCO cycles going low
just before the transmission of bit 15 and going high just
after the transmission of bit 0. If a logic Low is applied to
SFMT, FSO will be high for approximately one SCO cycle
and fall low just before the transmission of bit 15 and stay
low for the remainder of the transmission frame. If a logic
High is applied to SFMT, FSO will be low during the transmission of bits 15 –0 and high during the next 16 SCO cycles. See Figure 3 .
The Frame Sync Input (FSI), is used to synchronize the
ADC16071/ADC16471’s conversions to an external source.
The logic state of FSI is captured by the ADC16071/
ADC16471 on the falling edge of CLK. If an FSI low to high
transition is sensed between adjacent CLK falling edges,
the ADC16071/ADC16471 will interrupt its current data
transmission frame and begin a new one. See Figure 4 .
TWO CHANNEL MULTIPLEXED OPERATION
Two ADC16071/ADC16471’s can easily be configured to
share a single serial data line and operate in a ‘‘stereo’’, or
two channel multiplexed mode. They share the serial data
bus by alternating transmission of conversion data on their
respective SDO pins. One of the ADC16071/ADC16471’s,
the Master, shifts its conversion data out of SDO during the
first 16 SCO cycles of the data transmission frame. The
other ADC16071/ADC16471, the Slave, shifts its data out
during the second 16 SCO cycles of the data transmission
frame.
The Slave is selected by applying a logic High to its TSI pin
and a logic High to its SFMT pin. The Master is chosen by
applying a logic Low to its TSI pin and a logic High to its
SFMT pin. As shown in Figure 8 , the Master’s FSO is used
to control the DOE of both the Master and the Slave as well
as to synchronize the two ADC16071/ADC16471’s by driving the Slave’s Frame Sync Input pin, FSI. As the Master
finishes transmitting its 16 bits of conversion data, its FSO
goes High. This triggers the Slave’s FSI, causing the Slave
to begin transmitting its 16 bits of conversion data.
The Master’s DOE is active Low and the Slave’s DOE is
active High. Since the same signal, the Master’s FSO, is
connected to both of the converters’ DOE pins, one converter will shift out data on its SDO pin while the other is in
TRI-STATE, allowing the two ADC16071/ADC16471’s to
share the same serial data transmission line.
POWER SUPPLY AND GROUNDING
The ADC16071/ADC16471 has on-chip 50 pF bypass capacitors between the supply-pin bonding pads and their corresponding grounds. There are 24 of these capacitors, 6 for
the analog section and 18 for the digital, resulting in a total
value of 1200 pF. They help control ringing on the on-chip
power supply busses, especially in the digital section. Further, they help enhance the baseband noise performance of
the analog modulator.
14
Applications Information (Continued)
TL/H/11454 – 14
FIGURE 8. Two Channel Multiplexed Operation Connection Diagram
Best converter performance is achieved when these internal bypass capacitors are supplemented with additional external power-supply decoupling capacitors. This ensures the
lowest ac-bypass impedance path for the ADC16071/
ADC16471’s dynamic current requirements. Each of the
ADC16071/ADC16471’s four supply pins should be individually bypassed, using a parallel combination of 10 mF (tantalum) and 0.1 mF (monolithic ceramic), to its corresponding
ground pin:
VA a (Pin 21) x AGND (Pin 4)
VM a (Pin 20) x MGND (Pin 5)
VD a (Pin 19) x DGND (Pin 6)
VD a (Pin 18) x DGND (Pin 7)
Short lead lengths are mandatory. Therefore, surface mount
capacitors are strongly recommended.
ANALOG INPUT
The ADC16071 and the ADC16471 generate a two’s complement output determined by the following equation:
(VIN a b VINb) (32768)
(VREF a b VREFb)
Round off to the nearest integer value between b32768
and 32767.
The signals applied to VIN a and VINb must be between
VA a and analog ground. For accurate conversions, the absolute difference between VIN a and VINb should be less
than the difference between VREF a and VREFb. Best harmonic performance will result when a differential voltage is
applied to VIN a and VINb that has a common mode voltage
at or below VMID.
Due to overloading in the ADC16071/ADC16471’s DR modulator, performance degrades considerably as the input amplitude approaches full scale. With an input that peaks at
b 2 dB from full scale, S/(N a D) is about 2 dB worse than
with a b6 dB input. With a b1 dB input, S/(N a D) can be
10 dB worse than with a b6 dB input.
Output Code e
POWER SUPPLY VOLTAGES FOR BEST
PERFORMANCE
While adequate performance will be achieved by operating
the ADC16071/ADC16471 with a 5V connected to VA a ,
VM a and VD a , dynamic performance, as measured by
S/(N a D), can be further enhanced by slightly raising the
analog supply voltage and lowering the digital supply voltage.
15
Applications Information (Continued)
ANALOG SIGNAL CONDITIONING
The ADC16071/ADC16471’s digital comb and FIR filter
combine to create the band-limiting anti-aliasing filter, generating a steep cutoff at the upper range of the sampled
baseband. Additional external filtering is needed to ensure
that the best conversion performance is maintained. The
external filtering uses a simple R-C lowpass filter. A suggested circuit is shown in Figure 9. The values of R1, R2, C1,
C2, and C3 are found using the following equation:
1
f c ( b 3 dB) e
6qRC
where R e R1 e R2 and C e C1 e C2 e C3.
The effects of the external filter are minimized by choosing
a minimum cutoff frequency equal to fCLK/32. As an example, for fCLK equal to 6.144 MHz, set R1 e R2 e 82.5X and
C1 e C2 e C3 e 3300 pF. This sets the input network’s
cutoff frequency at 194 kHz. For fCLK equal to 24.576 MHz,
set R1 e R2 e 20X and C1 e C2 e C3 e 3300 pF. This
sets the input network’s cutoff frequency at 803 kHz.
have film dielectrics. Of these, polypropylene and polystyrene are the best. These are followed by polycarbonate and
mylar. If ceramic capacitors are chosen, use only capacitors
with NPO dielectrics.
INTERNAL DIFFERENTIAL BANDGAP REFERENCE
A fully differential bandgap reference generates local feedback voltages, VREF a and VREFb, for the analog modulator. The outputs of this reference are trimmed to be equal to
VMID plus or minus 1.25V. This gives a differential reference
voltage of 2.5V which results in a g 2.5V differential input
range. The ADC16071 does not have the internal differential bandgap reference, allowing the user the flexibility to
determine the full scale range by using an external voltage
reference.
EXTERNAL VOLTAGE REFERENCE FOR THE
ADC16071
Figure 10 shows the suggested connection diagram for the
ADC16071. The LM4041-ADJ is set to 2.0V and is applied
to the ADC16071’s VREF a input.
The reference voltage must be free of noise. This is accomplished using the same capacitor combination used with the
ADC16471’s reference pins with the exception of VREFb,
which is connected to analog ground.
Figures 11 and 12 show the suggested circuits for ac-coupled applications.
RELATION BETWEEN CAPACITOR DIELECTRIC AND
SIGNAL DISTORTION
For any capacitors connected to the ADC16071/
ADC16471’s analog inputs, the dielectric plays an important
role in determining the amount of distortion generated in the
input signal. The capacitors used must have low dielectric
absorption. This requirement is fulfilled using capacitors that
Suggested values:
R1 e R2 e 20X, 5%, metal film
C1 e C2 e C3 e 3300 pF, 5%,
polypropylene
TL/H/11454 – 15
*Parallel combination of 10 mF tantalum and a 0.1 mF monolithic ceramic capacitors.
FIGURE 9. Typical Connection Diagram for the ADC16471
16
Applications Information (Continued)
Suggested values:
R1 e R2 e 20X, 5%, metal film
C1 e C2 e C3 e 3300 pF, 5%,
polypropylene
*Parallel combination of 10 mF tantalum and a 0.1 mF monolithic ceramic capacitors.
TL/H/11454 – 16
FIGURE 10. Typical Connection Diagram for the ADC16071
Suggested values:
R1 e R2 e 20X, 5%, metal film
C1 e C2 e C3 e 3300 pF, 5%,
polypropylene
*Parallel combination of 10 mF tantalum and a 0.1 mF monolithic ceramic capacitors.
TL/H/11454 – 17
FIGURE 11. Typical Connection Diagram for the ADC16471 with AC-Coupled Inputs
Suggested values:
R1 e R2 e 20X, 5%, metal film
C1 e C2 e C3 e 3300 pF, 5%,
polypropylene
*Parallel combination of 10 mF tantalum and a 0.1 mF monolithic ceramic capacitors.
TL/H/11454 – 18
FIGURE 12. Typical Connection Diagram for the ADC16071 with AC-Coupled Inputs
17
Applications Information (Continued)
DSP INTERFACES
The ADC16071/ADC16471 was designed to connect to popular DSPs without intervening ‘‘glue logic’’. Figures 13, 14, and 15
show suggested connection schematics for the DSP56001, TMS320C3x, and the ADSP-2101 families.
TL/H/11454 – 19
FIGURE 13. Interface Connections between the ADC16071/ADC16471 and the Motorola DSP56001
TL/H/11454 – 20
FIGURE 14. Interface Connections between the ADC16071/ADC16471 and the Texas Instruments TMS320C3x
TL/H/11454 – 21
FIGURE 15. Interface Connections between the ADC16071/ADC16471 and the Analog Devices ADSP-2101
18
Physical Dimensions inches (millimeters)
24-Lead (0.300× Wide) Molded Small Outline Package, JEDEC
Order Number ADC16071CIWM or ADC16471CIWM
NS Package Number M24B
19
ADC16071/ADC16471 16-Bit Delta-Sigma 192 ks/s Analog-to-Digital Converters
Physical Dimensions inches (millimeters) (Continued)
24-Lead (0.300× Wide) Molded Dual-In-Line Package
Order Number ADC16071CIN or ADC16471CIN
NS Package Number N24C
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