ADC10461,ADC10462,ADC10464
ADC10461/ADC10462/ADC10464 10-Bit 600 ns A/D Converter with Input
Multiplexer and Sample/Hold
Literature Number: SNAS074D
ADC10461/ADC10462/ADC10464
10-Bit 600 ns A/D Converter with Input Multiplexer and
Sample/Hold
General Description
NOTE: The ADC10461 and ADC10462 are obsolete. They
are described here for reference only.
Using an innovative, patented multistep* conversion tech-
nique, these 10-bit CMOS analog-to-digital converters offer
sub-microsecond conversion times yet dissipate a maximum
of only 235 mW. These converters perform 10-bit conversion
in two lower-resolution “flashes”, yielding a fast A/D without
the cost, power consumption, and other problems associ-
ated with true flash approaches. Dynamic performance
(THD, S/N) is guaranteed.
The analog input voltage is sampled and held by an internal
sampling circuit. Input signals at frequencies from DC to over
200 kHz can, therefore, be digitized accurately without the
need for an external sample-and-hold circuit.
The ADC10462 and ADC10464 include a “speed-up” pin.
Connecting an external resistor between this pin and ground
reduces the typical conversion time to as little as 350 ns with
only a small increase in linearity error.
For ease of interface to microprocessors, the ADC10461,
ADC10462, and ADC10464 have been designed to appear
as a memory location or I/O port without the need for exter-
nal interface logic.
Features
nBuilt-in sample-and-hold
nSingle +5V supply
nNo external clock required
nSpeed adjust pin for faster conversions (ADC10462 and
ADC10464)
Key Specifications
nConversion Time 600 ns (typical)
nSampling Rate 800 kHz
nLow Power Consumption 235 mW (max)
nTotal Harmonic Distortion (50 kHz) −60 dB (max)
nNo Missing Codes Over Temperature
Applications
nDigital signal processor front ends
nInstrumentation
nDisk drives
nMobile telecommunications
Note: *U.S. Patent Number 4918449
Simplified Block Diagram
01110809
*ADC10461 Only
**ADC10462 and ADC10464 Only
***ADC10464 Only
April 2006
ADC10461/ADC10462/ADC10464 10-Bit 600 ns A/D Converter with Input Multiplexer and
Sample/Hold
© 2006 National Semiconductor Corporation DS011108 www.national.com
Ordering Information
Industrial Temp Range
(−40˚C ≤T
A
≤+85˚C) Channels Package
ADC10461CIWM * 1 M20B Small Outline
ADC10461CIWMX * 1 M20B Small Outline Tape & Real
ADC10462CIWM * 2 M24B Small Outline
ADC10462CIWMX * 2 M24B Small Outline Tape & Real
ADC10464CIWM 4 M28B Small Outline
ADC10464CIWMX 4 M28B Small Outline Tape & Real
* These devices are obsolete; shown for reference only.
Connection Diagrams
01110810
This device is obsolete; shown for reference only.
Top View 01110811
This device is obsolete; shown for reference only.
Top View 01110812
Top View
NOTE: The ADC10461 and ADC10462 are obsolete; shown for reference only.
ADC10461/ADC10462/ADC10464
www.national.com 2
Pin Descriptions
Pin Function Description
DV
CC
,AV
CC
Digital and analog positive supply voltage inputs. Connect both to the same voltage source, but
bypass separately with a 0.1 µF ceramic capacitor in parallel with a 10 µF tantalum capacitor to
ground at each pin.
INT Active low interrupt output. INT goes low at the end of each conversion, and returns high
following the rising edge of RD.
S/H Sample/Hold control input. When this pin is forced low (and CS is low), the analog input signal is
sampled and a new conversion is initiated.
RD Active low read control input. When this RD and CS are low, any data present in the output
registers will be placed onto the data bus.
CS Active low Chip Select control input. When low, this pin enables the RD and S/H pins.
S0, S1 On the multiple-input devices (ADC10462 and ADC10464), these pins select the analog input
that will be connected to the A/D during the conversion. The input is selected based on the state
of S0 and S1 when S/H makes its High-to-Low transition (See the Timing Diagrams). The
ADC10464 includes both S0 and S1. The ADC10462 includes just S0, and the ADC10461 has
neither.
V
REF−
,V
REF+
Reference voltage inputs. They may be placed at any voltage between GND and V
CC
, but V
REF+
must be greater than V
REF−
. An input voltage equal to V
REF−
produces an output code of 0, and
an input voltage equal to (V
REF+
− 1 LSB) produces an output code of 1023.
V
IN
,V
IN0
,V
IN1
,
V
IN2
,V
IN3
Analog input pins. The ADC10461 has one input (V
IN
), the ADC10462 has two inputs (V
IN0
and
V
IN1
), and the ADC10464 has four inputs (V
IN0
,V
IN1
,V
IN2
and V
IN3
). The impedance of the input
source should be less than 500Ωfor best accuracy and conversion speed. For accurate
conversions, no input pin (even one that is not selected) should be driven more than 50 mV
above V
CC
or 50 mV below ground.
GND, AGND,
DGND
Power supply ground pins. The ADC10461 has a single ground pin (GND), and the ADC10462
and ADC10464 have separate analog and digital ground pins (AGND and DGND) for separate
bypassing of the analog and digital supplies. The ground pins should be connected to a stable,
noise-free system ground. For the devices with two ground pins, both pins should be returned to
the same potential.
DB0–DB9 TRI-STATE®data output pins.
SPEED ADJ (ADC10462 and ADC10464 only). This pin is normally left unconnected, but by connecting a
resistor between this pin and ground, the conversion time can be reduced. See the Typical
Performance Curves and the table of Electrical Characteristics.
ADC10461/ADC10462/ADC10464
www.national.com3
Absolute Maximum Ratings
(Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
+
=AV
CC
=DV
CC
) −0.3V to +6V
Voltage at Any Input or Output −0.3V to V
+
+ 0.3V
Input Current at Any Pin (Note 3) 5 mA
Package Input Current (Note 3) 20 mA
Power Consumption (Note 4) 875 mW
ESD Susceptibility (Note 5) 2000V
Soldering Information (Note 6)
N Package (10 Sec) 260˚C
SO Package:
Vapor Phase (60 Sec) 215˚C
Infrared (15 Sec) 220˚C
Storage Temperature Range −65˚C to +150˚C
Junction Temperature 150˚C
Operating Ratings (Notes 1, 2)
Temperature Range T
MIN
≤T
A
≤T
MAX
=
−40˚C ≤T
A
≤+85˚C
Supply Voltage Range +4.5V to +5.5V
Package Thermal Resistance
Device θ
JA
(˚C/W)
ADC10461CIWM 85
ADC10462CIWM 82
ADC10464CIWM 78
Converter Characteristics
The following specifications apply for V
+
= +5V, V
REF(+)
= +5V, V
REF(−)
= GND, and Speed Adjust pin unconnected unless oth-
erwise specified. Boldface limits apply for T
A
=T
J
=T
Min
to T
Max
;all other limits T
A
=T
J
= +25˚C.
Symbol Parameter Conditions Typical
(Note 7)
Limit
(Note 8)
Units
(Limit)
Resolution 10 Bits
Integral Linearity Error R
SA
≥18 kΩ±0.5 LSB
Offset Error ±1.5 LSB (max)
Full-Scale Error ±1LSB (max)
Total Unadjusted Error R
SA
≥18 kΩ±0.5 LSB
Missing Codes 0(max)
Power Supply Sensitivity V
+
=5V±5%, V
REF
= 4.5V ±1/16 LSB
V
+
=5V±10%, V
REF
= 4.5V ±
1
⁄
8
LSB
THD Total Harmonic Distortion
f
IN
= 1 kHz, 4.85 V
P-P
f
IN
= 50 kHz, 4.85 V
P-P
f
IN
= 100 kHz, 4.85 V
P-P
f
IN
= 240 kHz, 4.85 V
P-P
−68
−66
−62
−58
−60
dB
dB (max)
dB
dB
SNR Signal-to-Noise Ratio
f
IN
= 1 kHz, 4.′85 V
P-P
f
IN
= 50 kHz, 4.85 V
P-P
f
IN
= 100 kHz, 4.85 V
P-P
61
60
60
58
dB
dB (min)
dB
ENOB Effective Number of Bits f
IN
= 1 kHz, 4.85 V
P-P
f
IN
= 50 kHz, 4.85 V
P-P
9.6
9.5 9
Bits
Bits (min)
R
REF
Reference Resistance 650 400 Ω(min)
R
REF
Reference Resistance 650 900 Ω(max)
V
REF(+)
V
REF(+)
Input Voltage V
+
+ 0.05 V (max)
V
REF(−)
V
REF(−)
Input Voltage GND − 0.05 V (min)
V
REF(+)
V
REF(+)
Input Voltage V
REF(−)
V (min)
V
REF(−)
V
REF(−)
Input Voltage V
REF(+)
V (max)
V
IN
Input Voltage V
+
+ 0.05 V (max)
V
IN
Input Voltage GND − 0.05 V (min)
OFF Channel Input Leakage Current CS = V
+
,V
IN
=V
+
0.01 3µA (max)
ON Channel Input Leakage Current CS = V
+
,V
IN
=V
+
±1−3 µA (max)
ADC10461/ADC10462/ADC10464
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DC Electrical Characteristics
The following specifications apply for V
+
= +5V, V
REF(+)
=5VV
REF(−)
= GND, and Speed Adjust pin unconnected unless other-
wise specified. Boldface limits apply for T
A
=T
J
=T
MIN
to T
MAX
;all other limits T
A
=T
J
= +25˚C.
Symbol Parameter Conditions Typical
(Note 7)
Limit (Note
8)
Units
(Limits)
V
IN(1)
Logical “1” Input Voltage V
+
= 5.5V 2.0 V (min)
V
IN(0)
Logical “0” Input Voltage V
+
= 4.5V 0.8 V (max)
I
IN(1)
Logical “1” Input Current V
IN(1)
= 5V 0.005 3.0 µA (max)
I
IN(0)
Logical “0” Input Current V
IN(0)
0V −0.005 −3.0 µA (max)
V
OUT(1)
Logical “1” Output Voltage V
+
= 4.5V, I
OUT
= −360 µA 2.4 V (min)
V
+
= 4.5V, I
OUT
= −10 µA 4.25 V (min)
V
OUT(0)
Logical “0” Output Voltage V
+
= 4.5V, I
OUT
= 1.6 mA 0.4 V (max)
I
OUT
TRI-STATE Output Current V
OUT
=5V
V
OUT
=0V
0.1
−0.1
50
−50
µA (max)
µA (max)
DI
CC
DV
CC
Supply Current CS=S/H=RD=0,R
SA
=∞
CS=S/H=RD=0,R
SA
=18kΩ
1.0
1.0
2mA (max)
mA (max)
AI
CC
AV
CC
Supply Current CS=S/H=RD=0,R
SA
=∞
CS=S/H=RD=0,R
SA
=18kΩ
30
30
45 mA (max)
mA (max)
AC Electrical Characteristics
The following specifications apply for V
+
= +5V, t
r
=t
f
= 20 ns, V
REF(+)
= 5V, V
REF(−)
= GND, and Speed Adjust pin uncon-
nected unless otherwise specified. Boldface limits apply for T
A
=T
J
=T
MIN
to T
MAX
;all other limits T
A
=T
J
= +25˚C.
Symbol Parameter Conditions Typical
(Note 7)
Limit (Note
8)
Units
(Limits)
t
CONV
Mode 1 Conversion Time from Rising
Edge of S /H to Falling Edge of INT
CIN, CIWM Suffixes
R
SA
= 18k
600
375
750/900 ns (max)
ns
t
CRD
Mode 2 Conversion Time CIN, CIWM Suffixes
Mode 2, R
SA
= 18k
850
530
1400 ns (max)
ns
t
ACC1
Access Time (Delay from Falling
Edge of RD to Output Valid) Mode 1; C
L
= 100 pF 30 60 ns (max)
t
ACC2
Access Time (Delay from Falling
Edge of RD to Output Valid) Mode 2; C
L
= 100 pF 900 t
CRD
+50 ns (max)
t
SH
Minimum Sample Time (Figure 1) ; (Note 9) 250 ns (max)
t
1H
,t
0H
TRI-STATE Control (Delay from
Rising Edge of RD to High-Z State) R
L
= 1k, C
L
=10pF 30 60 ns (max)
t
INTH
Delay from Rising Edge of RD to
Rising Edge of INT C
L
= 100 pF 25 50 ns (max)
t
P
Delay from End of Conversion to
Next Conversion 50 ns (max)
t
MS
Multiplexer Control Setup Time 10 75 ns (max)
t
MH
Multiplexer Hold Time 10 40 ns (max)
C
VIN
Analog Input Capacitance 35 pF (max)
C
OUT
Logic Output Capacitance 5 pF (max)
C
IN
Logic Input Capacitance 5 pF (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. These ratings do not guarantee specific performance limits, however. For guaranteed specifications and test conditions, see the Electrical Characteristics.
The guaranteed specifications apply only 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 <GND or VIN >V+) the absolute value of current at that pin should be limited
to 5 mA or less. The 20 mA package input current limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four.
Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,θJA and the ambient temperature, TA. The maximum
allowable power dissipation at any temperature is PD=(T
JMAX −T
A)/θJA or the number given in the Absolute Maximum Ratings, whichever is lower. In most cases,
the maximum derated power dissipation will be reached only during fault conditions. For these devices, TJMAX for a board-mounted device can be in from the
Package Thermal Tables.
Note 5: Human body model, 100 pF discharged through a 1.5 kΩresistor.
ADC10461/ADC10462/ADC10464
www.national.com5
AC Electrical Characteristics (Continued)
Note 6: See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National
Semiconductor Linear Data Book for other methods of soldering surface mount devices.
Note 7: Typical figures represent most likely parametric norm.
Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 9: Accuracy may degrade if tSH is shorter than the value specified. See curves of Accuracy vs. tSH.
TRI-STATE Test Circuits and Waveforms
01110803
01110804
01110805
01110806
ADC10461/ADC10462/ADC10464
www.national.com 6
Timing Diagrams
01110807
FIGURE 1. Mode 1. The conversion time (t
CONV
) is set by the internal timer.
01110808
FIGURE 2. Mode 2 (RD Mode). The conversion time (t
CRD
) includes the
sampling time and is determined by the internal timer.
ADC10461/ADC10462/ADC10464
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Typical Performance Characteristics
Zero (Offset) Error
vs. Reference Voltage
Linearity Error
vs. Reference Voltage
01110815 01110816
Analog Supply Current
vs. Temperature
Digital Supply Current
vs. Temperature
01110817 01110818
Conversion Time
vs. Temperature
Conversion Time
vs. Temperature
01110819 01110820
ADC10461/ADC10462/ADC10464
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Typical Performance Characteristics (Continued)
Conversion Time
vs. Speed-Up Resistor
(ADC10462 and ADC10464 Only)
Conversion Time
vs. Speed-Up Resistor
(ADC10462 and ADC10464 Only)
01110821 01110822
Spectral Response with
100 kHz Sine Wave Input
Spectral Response with
100 kHz Sine Wave Input
01110823 01110824
Signal-to-Noise + THD Ratio
vs. Signal Frequency
Linearity Change
vs. Speed-Up Resistor
(ADC10462 and ADC10464 Only)
01110825 01110826
ADC10461/ADC10462/ADC10464
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Typical Performance Characteristics (Continued)
Linearity Change
vs. Speed-Up Resistor
(ADC10462 and ADC10464 Only)
Linearity Error Change
vs. Sample Time
01110827 01110828
ADC10461/ADC10462/ADC10464
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Functional Description
The ADC10461 and the ADC10462 are obsolete and dis-
cussed here for reference only.
The ADC10461, ADC10462 and ADC10464 digitize an ana-
log input signal to 10 bits accuracy by performing two lower-
resolution “flash” conversions. The first flash conversion pro-
vides the six most significant bits (MSBs) of data, and the
second flash conversion provides the four least significant
bits LSBs).
Figure 3 is a simplified block diagram of the converter. Near
the center of the diagram is a string of resistors. At the
bottom of the string of resistors are 16 resistors, each of
which has a value 1/1024 the resistance of the whole resistor
string. These lower 16 resistors (the LSB Ladder ) therefore
have a voltage drop of 16/1024, or 1/64 of the total reference
voltage (V
REF+
−V
REF−
) across them. The remainder of the
resistor string is made up of eight groups of eight resistors
connected in series. These comprise the MSB Ladder .
Each section of the MSB Ladder has
1
⁄
8
of the total reference
voltage across it, and each of the LSB resistors has 1/64 of
the total reference voltage across it. Tap points across these
resistors can be connected, in groups of sixteen, to the
sixteen comparators at the right of the diagram.
On the left side of the diagram is a string of seven resistors
connected between V
REF+
and V
REF−
. Six comparators com-
pare the input voltage with the tap voltages on this resistor
string to provide a low-resolution “estimate” of the input
voltage. This estimate is then used to control the multiplexer
that connects the MSB Ladder to the sixteen comparators on
the right. Note that the comparators on the left needn’t be
very accurate; they simply provide an estimate of the input
voltage. Only the sixteen comparators on the right and the
six on the left are necessary to perform the initial six-bit flash
conversion, instead of the 64 comparators that would be
required using conventional half-flash methods.
To perform a conversion, the estimator compares the input
voltage with the tap voltages on the seven resistors on the
left. The estimator decoder then determines which MSB
Ladder tap points will be connected to the sixteen compara-
tors on the right. For example, assume that the estimator
determines that V
IN
is between 11/16 and 13/16 of V
REF
. The
estimator decoder will instruct the comparator MUX to con-
nect the 16 comparators to the taps on the MSB ladder
between 10/16 and 14/16 of V
REF
. The 16 comparators will
then perform the first flash conversion. Note that since the
comparators are connected to ladder voltages that extend
beyond the range indicated by the estimator circuit, errors in
the estimator as large as 1/16 of the reference voltage
(64 LSBs) will be corrected. This first flash conversion pro-
duces the six most significant bits of data — four bits in the
flash itself, and 2 bits in the estimator.
The remaining four LSBs are now determined using the
same sixteen comparators that were used for the first flash
conversion. The MSB Ladder tap voltage just below the input
voltage (as determined by the first flash) is subtracted from
the input voltage and compared with the tap points on the
sixteen LSB Ladder resistors. The result of this second,
four-bit flash conversion is then decoded, and the full 10-bit
result is latched.
Note that the sixteen comparators used in the first flash
conversion are reused for the second flash. Thus, the multi-
step conversion technique used in the ADC10461,
ADC10462, and ADC10464 needs only a small fraction of
the number of comparators that would be required for a
traditional flash converter, and far fewer than would be used
in a conventional half-flash approach. This allows the
ADC10461, ADC10462, and ADC10464 to perform high-
speed conversions without excessive power drain.
ADC10461/ADC10462/ADC10464
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Functional Description (Continued)
SIMILAR PRODUCT DIFFERENCES
The ADC1046x, ADC1046x and ADC1066x (where "x" indi-
cates the number of multiplexer inputs) are similar devices
with different specification limits. The differences in these
device families are summarized below.
Device
Family
ILE, TUE,
PSS
THD, SNR,
ENOB
Max.
Conversion
Time
ADC1046x Guaranteed - 900ns
ADC1046x - Guaranteed 900ns
ADC1066x - Guaranteed 466ns
Applications Information
1.0 MODES OF OPERATION
The ADC10461, ADC10462, and ADC10464 have two basic
digital interface modes. Figure 1 and Figure 2 are timing
diagrams for the two modes. The ADC10462 and ADC10464
have input multiplexers that are controlled by the logic levels
on pins S
0
and S
1
when S/H goes low. Tables 1, 2 are truth
tables showing how the input channels are assigned.
Mode 1
In this mode, the S/H pin controls the start of conversion. S/H
is pulled low for a minimum of 250 ns. This causes the
comparators in the “coarse” flash converter to become ac-
tive. When S/H goes high, the result of the coarse conver-
sion is latched and the “fine” conversion begins. After 600 ns
(typical), INT goes low, indicating that the conversion results
are latched and can be read by pulling RD low. Note that CS
must be low to enable S/H or RD. CS is internally “ANDed”
with S/H and RD; the input voltage is sampled when CS and
S/H are low, and data is read when CS and RD are low. INT
is reset high on the rising edge of RD.
TABLE 1. Input Multiplexer Programming
ADC10464
S
1
S
0
Channel
00 V
IN0
01 V
IN1
10 V
IN2
11 V
IN3
TABLE 2. Input Multiplexer Programming
ADC10462
S
0
Channel
0V
IN0
1V
IN1
Mode 2
In Mode 2, also called “RD mode”, the S/H and RD pins are
tied together. A conversion is initiated by pulling both pins
low. The A/D converter samples the input voltage and
causes the coarse comparators to become active. An inter-
nal timer then terminates the coarse conversion and begins
the fine conversion. 850 ns (typical) after S/H and RD are
pull low, INT goes low, indicating that the conversion is
01110813
FIGURE 3. Block Diagram of the Multistep Converter Architecture
ADC10461/ADC10462/ADC10464
www.national.com 12
Applications Information (Continued)
completed. Approximately 20 ns later the data appearing on
the TRI-STATE output pins will be valid. Note that data will
appear on these pins throughout the conversion, but until
INT goes low the data at the output pins will be the result of
the previous conversion.
2.0 REFERENCE CONSIDERATIONS
The ADC10461, ADC10462, and ADC10464 each have two
reference inputs. These inputs, V
REF+
and V
REF−
, are fully
differential and define the zero to full-scale range of the input
signal. The reference inputs can be connected to span the
entire supply voltage range (V
REF−
=0V,V
REF+
=V
CC
) for
ratiometric applications, or they can be connected to differ-
ent voltages (as long as they are between ground and V
CC
)
when other input spans are required.
Reducing the overall V
REF
span to less than 5V increases
the sensitivity of the converter (e.g., if V
REF
= 2V, then 1 LSB
= 1.953 mV). Note, however, that linearity and offset errors
become larger when lower reference voltages are used. See
the Typical Performance Curves for more information. For
this reason, reference voltages less than 2V are not recom-
mended.
In most applications, V
REF−
will simply be connected to
ground, but it is often useful to have an input span that is
offset from ground. This situation is easily accommodated by
the reference configuration used in the ADC10461,
ADC10462, and ADC10464. V
REF−
can be connected to a
voltage other than ground as long as the voltage source
connected to this pin is capable of sinking the converter’s
reference current (12.5 mA Max @V
REF
= 5V). If V
REF−
is
connected to a voltage other than ground, bypass it with
multiple capacitors.
Since the resistance between the two reference inputs can
be as low as 400Ω, the voltage source driving the reference
inputs should have low output impedance. Any noise on
either reference input is a potential cause of conversion
errors, so each of these pins must be supplied with a clean,
low noise voltage source. Each reference pin should be
bypassed with a 10 µF tantalum and a 0.1 µF ceramic.
3.0 THE ANALOG INPUT
The ADC10461, ADC10462, and ADC10464 sample the
analog input voltage once every conversion cycle. When this
happens, the input is briefly connected to an impedance
approximately equal to 600Ωin series with 35 pF. Short-
duration current spikes can be observed at the analog input
during normal operation. These spikes are normal and do
not degrade the converter’s performance.
Large source impedances can slow the charging of the
sampling capacitors and degrade conversion accuracy.
Therefore, only signal sources with output impedances less
than 500Ωshould be used if rated accuracy is to be
achieved at the minimum sample time (250 ns maximum). If
the sampling time is increased, the source impedance can
be larger. If a signal source has a high output impedance, its
output should be buffered with an operational amplifier. The
operational amplifier’s output should be well-behaved when
driving a switched 35 pF/600Ωload. Any ringing or voltage
shifts at the op amp’s output during the sampling period can
result in conversion errors.
Correct conversion results will be obtained for input voltages
greater than GND − 50 mV and less than V
+
+ 50 mV. Do not
allow the signal source to drive the analog input pin beyond
the Absolute Maximum Rating. If an analog input pin is
forced beyond these voltages, the current flowing through
the pin should be limited to 5 mA or less to avoid permanent
damage to the IC. The sum of all the overdrive currents into
all pins must be less than the Absolute Maximum Rating for
Package Input Current. When the input signal is expected to
extend beyond this limit, an input protection scheme should
be used. A simple input protection network using diodes and
resistors is shown in Figure 4. Note the multiple bypass
capacitors on the reference and power supply pins. If V
REF−
is not grounded, it should also be bypassed to analog ground
using multiple capacitors (see 5.0 “Power Supply Consider-
ations”). AGND and DGND should be at the same potential.
V
IN0
is shown with an input protection network. Pin 17 is
normally left open, but optional “speedup” resistor R
SA
can
be used to reduce the conversion time.
01110814
FIGURE 4. Typical Connection
ADC10461/ADC10462/ADC10464
www.national.com13
Applications Information (Continued)
4.0 INHERENT SAMPLE-AND-HOLD
Because the ADC10461, ADC10462, and ADC10464
sample the input signal once during each conversion, they
are capable of measuring relatively fast input signals without
the help of an external sample-hold. In a non-sampling
successive-approximation A/D converter, regardless of
speed, the input signal must be stable to better than ±1/2
LSB during each conversion cycle or significant errors will
result. Consequently, even for many relatively slow input
signals, the signals must be externally sampled and held
constant during each conversion if a SAR with no internal
sample-and-hold is used.
Because they incorporate a direct sample/hold control input,
the ADC10461, ADC10462, and ADC10464 are suitable for
use in DSP-based systems. The S/H input allows synchro-
nization of the A/D converter to the DSP system’s sampling
rate and to other ADC10461s, ADC10462s, and
ADC10464s.
5.0 POWER SUPPLY CONSIDERATIONS
The ADC10461, ADC10462, and ADC10464 are designed to
operate from a +5V (nominal) power supply. There are two
supply pins, AV
CC
and DV
CC
. These pins allow separate
external bypass capacitors for the analog and digital portions
of the circuit. To guarantee accurate conversions, the two
supply pins should be connected to the same voltage
source, and each should be bypassed with a 0.1 µF ceramic
capacitor in parallel with a 10 µF tantalum capacitor. De-
pending upon the circuit board layout and other system
considerations, more bypassing may be necessary.
The ADC10461 has a single ground pin, and the ADC10462
and ADC10464 each have separate analog and digital
ground pins for separate bypassing of the analog and digital
supplies. The devices with separate analog and digital
ground pins should have their ground pins connected to the
same potential, and all grounds should be “clean” and free of
noise.
In systems with multiple power supplies, careful attention to
power supply sequencing may be necessary to avoid over-
driving inputs. The A/D converter’s power supply pins should
be at the proper voltage before digital or analog signals are
applied to any of the other pins.
6.0 LAYOUT AND GROUNDING
In order to ensure fast, accurate conversions from the
ADC10461, ADC10462, and ADC10464, it is necessary to
use appropriate circuit board layout techniques. The analog
ground return path should be low-impedance and free of
noise from other parts of the system. Noise from digital
circuitry can be especially troublesome.
All bypass capacitors should be located as close to the
converter as possible and should connect to the converter
and to ground with short traces. The analog input should be
isolated from noisy signal traces to avoid having spurious
signals couple to the input. Any external component (e.g., a
filter capacitor) connected across the converter’s input
should be connected to a very clean ground return point.
Grounding the component at the wrong point will result in
reduced conversion accuracy.
7.0 DYNAMIC PERFORMANCE
Many applications require the A/D converter to digitize AC
signals, but conventional DC integral and differential nonlin-
earity specifications don’t accurately predict the A/D convert-
er’s performance with AC input signals. The important speci-
fications for AC applications reflect the converter’s ability to
digitize AC signals without significant spectral errors and
without adding noise to the digitized signal. Dynamic char-
acteristics such as signal-to-noise ratio (SNR) and total har-
monic distortion (THD), are quantitative measures of this
capability.
An A/D converter’s AC performance can be measured using
Fast Fourier Transform (FFT) methods. A sinusoidal wave-
form is applied to the A/D converter’s input, and the trans-
form is then performed on the digitized waveform. The re-
sulting spectral plot might look like the ones shown in the
typical performance curves. The large peak is the fundamen-
tal frequency, and the noise and distortion components (if
any are present) are visible above and below the fundamen-
tal frequency. Harmonic distortion components appear at
whole multiples of the input frequency. Their amplitudes are
combined as the square root of the sum of the squares and
compared to the fundamental amplitude to yield the THD
specification. Guaranteed limits for THD are given in the
table of Electrical Characteristics.
Signal-to-noise ratio is the ratio of the amplitude at the
fundamental frequency to the rms value at all other frequen-
cies, excluding any harmonic distortion components. Guar-
anteed limits are given in the Electrical Characteristics table.
An alternative definition of signal-to-noise ratio includes the
distortion components along with the random noise to yield a
signal-to-noise-plus-distortion ration, or S/(N + D).
The THD and noise performance of the A/D converter will
change with the frequency of the input signal, with more
distortion and noise occurring at higher signal frequencies.
One way of describing the A/D’s performance as a function
of signal frequency is to make a plot of “effective bits” versus
frequency. An ideal A/D converter with no linearity errors or
self-generated noise will have a signal-to-noise ratio equal to
(6.02n + 1.76) dB, where n is the resolution in bits of the A/D
converter. A real A/D converter will have some amount of
noise and distortion, and the effective bits can be found by:
where S/(N + D) is the ratio of signal to noise and distortion,
which can vary with frequency.
As an example, an ADC10461 with a 4.85 V
P-P
, 100 kHz
sine wave input signal will typically have a signal-to-noise-
plus-distortion ratio of 59.2 dB, which is equivalent to 9.54
effective bits. As the input frequency increases, noise and
distortion gradually increase, yielding a plot of effective bits
or S/(N + D) as shown in the typical performance curves.
8.0 SPEED ADJUST
In applications that require faster conversion times, the
Speed Adjust pin (pin 14 on the ADC10462, pin 17 on the
ADC10464) can significantly reduce the conversion time.
The speed adjust pin is connected to an on-chip current
source that determines the converter’s internal timing. By
connecting a resistor between the speed adjust pin and
ground as shown in Figure 4, the internal programming
current is increased, which reduces the conversion time. As
an example, an 18k resistor reduces the conversion time of
a typical part from 600 ns to 350 ns with no significant effect
on linearity. Using smaller resistors to further decrease the
conversion time is possible as well, although the linearity will
begin to degrade somewhat (see curves). Note that the
ADC10461/ADC10462/ADC10464
www.national.com 14
Applications Information (Continued)
resistor value needed to obtain a given conversion time will
vary from part to part, so this technique will generally require
some “tweaking” to obtain satisfactory results.
For applications that require guaranteed performance using
the speed adjust pin, the ADC10662 and ADC10664 are
tested and guaranteed for static and dynamic performance
with a fixed value of speed-up resistor.
ADC10461/ADC10462/ADC10464
www.national.com15
Physical Dimensions inches (millimeters) unless otherwise noted
Order Number ADC10461CIWM
NS Package Number M20B
Order Number ADC10462CIWM
NS Package Number M24B
ADC10461/ADC10462/ADC10464
www.national.com 16
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Order Number ADC10464CIWM
NS Package Number M28B
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.
For the most current product information visit us at www.national.com.
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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 AND GENERAL COUNSEL 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.
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Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
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www.national.com
ADC10461/ADC10462/ADC10464 10-Bit 600 ns A/D Converter with Input Multiplexer and
Sample/Hold
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