ADC121S051EVAL [NSC]
Single Channel, 200 to 500ksps, 12-Bit A/D Converter; 单通道， 200〜 500KSPS ， 12位A / D转换器
| 型号： | ADC121S051EVAL |
| 厂家： | 
National Semiconductor |
| 描述： | Single Channel, 200 to 500ksps, 12-Bit A/D Converter |
| 文件： | 总16页 (文件大小：725K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 2006
ADC121S051
Single Channel, 200 to 500 ksps, 12-Bit A/D Converter
General Description
Features
n Specified over a range of sample rates.
n 6-lead LLP and SOT-23 packages
n Variable power management
The ADC121S051 is a low-power, single channel CMOS
12-bit analog-to-digital converter with a high-speed serial
interface. Unlike the conventional practice of specifying per-
formance at a single sample rate only, the ADC121S051 is
fully specified over a sample rate range of 200 ksps to
500 ksps. The converter is based upon a successive-
approximation register architecture with an internal track-
and-hold circuit.
n Single power supply with 2.7V - 5.25V range
™
™
n SPI /QSPI /MICROWIRE/DSP compatible
Key Specifications
n DNL
n INL
n SNR
+0.5/-0.25 LSB (typ)
+0.45/-0.40 LSB (typ)
72.0 dB (typ)
The output serial data is straight binary, and is compatible
with several standards, such as SPI
MICROWIRE, and many common DSP serial interfaces.
™
™
,
QSPI
,
n Power Consumption
— 3.6V Supply
— 5.25V Supply
The ADC121S051 operates with a single supply that can
range from +2.7V to +5.25V. Normal power consumption
using a +3.6V or +5.25V supply is 1.7 mW and 8.7 mW,
respectively. The power-down feature reduces the power
consumption to as low as 2.6 µW using a +5.25V supply.
1.7 mW (typ)
8.7 mW (typ)
Applications
n Portable Systems
n Remote Data Acquisition
The ADC121S051 is packaged in 6-lead LLP and SOT-23
packages. Operation over the industrial temperature range
of −40˚C to +85˚C is guaranteed.
n Instrumentation and Control Systems
Pin-Compatible Alternatives by Resolution and Speed
All devices are fully pin and function compatible.
Resolution
Specified for Sample Rate Range of:
200 to 500 ksps
50 to 200 ksps
ADC121S021
ADC101S021
ADC081S021
500 ksps to 1 Msps
ADC121S101
12-bit
10-bit
8-bit
ADC121S051
ADC101S051
ADC101S101
ADC081S051
ADC081S101
Connection Diagram
20144605
Ordering Information
Order Code
Temperature Range
Description
Top Mark
ADC121S051CISD
ADC121S051CISDX
ADC121S051CIMF
ADC121S051CIMFX
ADC121S051EVAL
−40˚C to +85˚C
−40˚C to +85˚C
−40˚C to +85˚C
−40˚C to +85˚C
6-Lead LLP Package
X4C
X4C
6-Lead LLP Package, Tape and Reel
6-Lead SOT-23 Package
X13C
X13C
6-Lead SOT-23 Package, Tape & Reel
SOT-23 Evaluation Board
TRI-STATE® is a trademark of National Semiconductor Corporation
™
™
QSPI and SPI are trademarks of Motorola, Inc.
© 2006 National Semiconductor Corporation
DS201446
www.national.com
Block Diagram
20144607
Pin Descriptions and Equivalent Circuits
Pin No.
Symbol
Description
ANALOG I/O
3
VIN
Analog input. This signal can range from 0V to VA.
DIGITAL I/O
4
SCLK
SDATA
CS
Digital clock input. This clock directly controls the conversion and readout processes.
Digital data output. The output samples are clocked out of this pin on falling edges of
the SCLK pin.
5
6
Chip select. On the falling edge of CS, a conversion process begins.
POWER SUPPLY
Positive supply pin. This pin should be connected to a quiet +2.7V to +5.25V source
and bypassed to GND with a 1 µF capacitor and a 0.1 µF monolithic capacitor located
within 1 cm of the power pin.
1
VA
2
GND
GND
The ground return for the supply and signals.
For package suffix CISD(X) only, it is recommended that the center pad should be
connected to ground.
PAD
www.national.com
2
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.
Operating Ratings (Notes 1, 2)
Operating Temperature Range
−40˚C ≤ TA ≤ +85˚C
VA Supply Voltage
+2.7V to +5.25V
Digital Input Pins Voltage Range
(regardless of supply voltage)
Analog Input Pins Voltage Range
Clock Frequency
−0.3V to +5.25V
Analog Supply Voltage VA
Voltage on Any Digital Pin to GND
Voltage on Any Analog Pin to GND
Input Current at Any Pin (Note 3)
Package Input Current (Note 3)
Power Consumption at TA = 25˚C
ESD Susceptibility (Note 5)
Human Body Model
−0.3V to 6.5V
−0.3V to 6.5V
−0.3V to (VA +0.3V)
10 mA
0V to VA
1 MHz to 10 MHz
up to 500 ksps
Sample Rate
20 mA
See (Note 4)
Package Thermal Resistance
Package
θJA
3500V
300V
6-lead LLP
94˚C / W
265˚C / W
Machine Model
6-lead SOT-23
Junction Temperature
+150˚C
Storage Temperature
−65˚C to +150˚C
Soldering process must comply with National Semiconduc-
tor’s Reflow Temperature Profile specifications. Refer to
www.national.com/packaging. (Note 6)
ADC121S051 Converter Electrical Characteristics (Notes 7, 9)
The following specifications apply for VA = +2.7V to 5.25V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps,
CL = 15 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C.
Limits
(Note 9)
Symbol
Parameter
Conditions
Typical
Units
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes
12
Bits
+0.45
−0.40
+0.75
−0.45
+0.50
−0.25
+0.80
−0.50
−0.18
+1.9
LSB (max)
LSB (min)
LSB (max)
LSB (min)
LSB (max)
LSB (min)
LSB (max)
LSB (min)
VA = +2.7V to +3.6V
1.0
INL
Integral Non-Linearity
VA = +4.75 to +5.25V
VA = +2.7V to +3.6V
VA = +4.75 to +5.25V
+1.0
−0.9
DNL
Differential Non-Linearity
VA = +2.7V to +3.6V
VA = +4.75 to +5.25V
VA = +2.7V to +3.6V
VA = +4.75 to +5.25V
1.2
1.5
VOFF
GE
Offset Error
Gain Error
LSB (max)
LSB (max)
−0.62
−1.50
DYNAMIC CONVERTER CHARACTERISTICS
VA = +2.7V to 5.25V
SINAD
SNR
Signal-to-Noise Plus Distortion Ratio
Signal-to-Noise Ratio
72
72
70
dB (min)
dB (min)
dB
fIN = 100 kHz, −0.02 dBFS
VA = +2.7V to 5.25V
70.8
fIN = 100 kHz, −0.02 dBFS
VA = +2.7V to 5.25V
THD
Total Harmonic Distortion
Spurious-Free Dynamic Range
Effective Number of Bits
−83
84
fIN = 100 kHz, −0.02 dBFS
VA = +2.7V to 5.25V
SFDR
ENOB
dB
fIN = 100 kHz, −0.02 dBFS
VA = +2.7V to 5.25V
11.7
−83
−82
11.3
Bits (min)
dB
fIN = 100 kHz, −0.02 dBFS
VA = +5.25V
Intermodulation Distortion, Second
Order Terms
fa = 103.5 kHz, fb = 113.5 kHz
VA = +5.25V
IMD
Intermodulation Distortion, Third
Order Terms
dB
fa = 103.5 kHz, fb = 113.5 kHz
3
www.national.com
ADC121S051 Converter Electrical Characteristics (Notes 7, 9) (Continued)
The following specifications apply for VA = +2.7V to 5.25V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps,
CL = 15 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C.
Limits
(Note 9)
Symbol
DYNAMIC CONVERTER CHARACTERISTICS
FPBW -3 dB Full Power Bandwidth
ANALOG INPUT CHARACTERISTICS
Parameter
Conditions
Typical
Units
VA = +5V
VA = +3V
11
8
MHz
MHz
VIN
Input Range
0 to VA
V
µA (max)
pF
IDCL
DC Leakage Current
1
Track Mode
Hold Mode
30
4
CINA
Input Capacitance
pF
DIGITAL INPUT CHARACTERISTICS
VA = +5.25V
VA = +3.6V
VA = +5V
2.4
2.1
0.8
0.4
1
V (min)
V (min)
VIH
VIL
Input High Voltage
Input Low Voltage
V (max)
V (max)
µA (max)
pF (max)
VA = +3V
IIN
Input Current
VIN = 0V or VA
0.1
2
CIND
Digital Input Capacitance
4
DIGITAL OUTPUT CHARACTERISTICS
ISOURCE = 200 µA
ISOURCE = 1 mA
ISINK = 200 µA
ISINK = 1 mA
VA − 0.07 VA − 0.2
V (min)
VOH
VOL
Output High Voltage
VA − 0.1
V
V (max)
V
0.03
0.1
0.4
Output Low Voltage
IOZH
IOZL
COUT
,
TRI-STATE® Leakage Current
0.1
2
10
4
µA (max)
pF (max)
TRI-STATE® Output Capacitance
Output Coding
Straight (Natural) Binary
POWER SUPPLY CHARACTERISTICS
2.7
V (min)
VA
Supply Voltage
5.25
V (max)
VA = +5.25V,
1.66
0.46
500
60
3.0
1.3
mA (max)
fSAMPLE = 200 ksps
VA = +3.6V,
Supply Current, Normal Mode
(Operational, CS low)
mA (max)
fSAMPLE = 200 ksps
VA = +5.25V, fSCLK = 0 MHz,
fSAMPLE = 0 ksps
IA
nA
µA
Supply Current, Shutdown (CS high)
VA = +5.25V, fSCLK = 10 MHz,
fSAMPLE = 0 ksps
VA = +5.25V
8.7
1.7
15.8
4.7
mW (max)
mW (max)
Power Consumption, Normal Mode
(Operational, CS low)
VA = +3.6V
VA = +5.25V, fSCLK = 0 MHz,
fSAMPLE = 0 ksps
PD
2.6
µW
µW
Power Consumption, Shutdown (CS
high)
VA = +5.25V, fSCLK = 10 MHz,
fSAMPLE = 0 ksps
315
AC ELECTRICAL CHARACTERISTICS
4
MHz (min)
MHz (max)
ksps (min)
ksps (max)
SCLK cycles
fSCLK
Clock Frequency
(Note 8)
(Note 8)
10
200
500
16
fS
Sample Rate
tCONV
Conversion Time
www.national.com
4
ADC121S051 Converter Electrical Characteristics (Notes 7, 9) (Continued)
The following specifications apply for VA = +2.7V to 5.25V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps,
CL = 15 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C.
Limits
(Note 9)
Symbol
Parameter
Conditions
Typical
Units
AC ELECTRICAL CHARACTERISTICS
40
60
% (min)
% (max)
ns (max)
SCLK cycles
ns (min)
ns
DC
SCLK Duty Cycle
fSCLK = 10 MHz
50
tACQ
Track/Hold Acquisition Time
Throughput Time
(Note 10)
400
20
Acquisition Time + Conversion Time
tQUIET
tAD
50
Aperture Delay
3
tAJ
Aperture Jitter
30
ps
ADC121S051 Timing Specifications
The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 4.0 MHz to 10.0 MHz, CL = 25 pF,
fSAMPLE = 200 ksps to 500 ksps, Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25˚C.
Symbol
tCS
Parameter
Minimum CS Pulse Width
Conditions
Typical
Limits
10
Units
ns (min)
ns (min)
tSU
CS to SCLK Setup Time
10
Delay from CS Until SDATA TRI-STATE®
Disabled (Note 11)
tEN
20
ns (max)
VA = +2.7V to +3.6V
40
ns (max)
ns (max)
ns (min)
ns (min)
ns (min)
ns (min)
ns (max)
ns (min)
ns (max)
ns (min)
µs
Data Access Time after SCLK Falling Edge
(Note 12)
tACC
VA = +4.75V to +5.25V
20
tCL
SCLK Low Pulse Width
SCLK High Pulse Width
0.4 x tSCLK
tCH
0.4 x tSCLK
VA = +2.7V to +3.6V
7
5
tH
SCLK to Data Valid Hold Time
VA = +4.75V to +5.25V
25
6
VA = +2.7V to +3.6V
SCLK Falling Edge to SDATA High
Impedance (Note 13)
tDIS
25
5
VA = +4.75V to +5.25V
tPOWER-UP
Power-Up Time from Full Power-Down
1
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 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 = 0V, unless otherwise specified.
<
>
V ), the current at that pin should be limited to 10 mA. The 20
Note 3: When the input voltage at any pin exceeds the power supply (that is, V
GND or V
IN
IN
A
mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 10 mA to two. The Absolute
Maximum Rating specification does not apply to the V pin. The current into the V pin is limited by the Analog Supply Voltage specification.
A
A
Note 4: The absolute maximum junction temperature (T max) for this device is 150˚C. The maximum allowable power dissipation is dictated by T max, the
J
J
junction-to-ambient thermal resistance (θ ), and the ambient temperature (T ), and can be calculated using the formula P max = (T max − T ) / θ . The values
JA
A
D
J
A
JA
for maximum power dissipation listed above will be reached only when the device is operated in a severe fault condition (e.g. when input or output pins are driven
beyond the power supply voltages, or the power supply polarity is reversed). Obviously, such conditions should always be avoided.
Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through zero ohms.
Note 6: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 7: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: This is the frequency range over which the electrical performance is guaranteed. The device is functional over a wider range which is specified under
Operating Ratings.
Note 9: Data sheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 10: Minimum Quiet Time required by bus relinquish and the start of the next conversion.
Note 11: Measured with the timing test circuit shown in Figure 1 and defined as the time taken by the output signal to cross 1.0V.
Note 12: Measured with the timing test circuit shown in Figure 1 and defined as the time taken by the output signal to cross 1.0V or 2.0V.
Note 13: t
is derived from the time taken by the outputs to change by 0.5V with the timing test circuit shown in Figure 1. The measured number is then adjusted
DIS
to remove the effects of charging or discharging the output capacitance. This means that t
is the true bus relinquish time, independent of the bus loading.
DIS
5
www.national.com
Timing Diagrams
20144608
FIGURE 1. Timing Test Circuit
20144606
FIGURE 2. ADC121S051 Serial Timing Diagram
www.national.com
6
MISSING CODES are those output codes that will never
appear at the ADC outputs. The ADC121S051 is guaranteed
not to have any missing codes.
Specification Definitions
ACQUISITION TIME is the time required to acquire the input
voltage. That is, it is time required for the hold capacitor to
charge up to the input voltage.
OFFSET ERROR is the deviation of the first code transition
(000...000) to (000...001) from the ideal (i.e. GND + 0.5
LSB).
APERTURE DELAY is the time between the fourth falling
SCLK edge of a conversion and the time when the input
signal is acquired or held for conversion.
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in
dB, of the rms value of the input signal to the rms value of the
sum of all other spectral components below one-half the
sampling frequency, not including harmonics or d.c.
APERTURE JITTER (APERTURE UNCERTAINTY) is the
variation in aperture delay from sample to sample. Aperture
jitter manifests itself as noise in the output.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD)
Is the ratio, expressed in dB, of the rms value of the input
signal to the rms value of all of the other spectral compo-
nents below half the clock frequency, including harmonics
but excluding d.c.
CONVERSION TIME is the time required, after the input
voltage is acquired, for the ADC to convert the input voltage
to a digital word.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-
ence, expressed in dB, between the desired signal ampli-
tude to the amplitude of the peak spurious spectral compo-
nent, where a spurious spectral component is any signal
present in the output spectrum that is not present at the input
and may or may not be a harmonic.
DUTY CYCLE is the ratio of the time that a repetitive digital
waveform is high to the total time of one period. The speci-
fication here refers to the SCLK.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion
or
SINAD.
ENOB
is
defined
as
TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-
pressed in dB or dBc, of the rms total of the first five
harmonic components at the output to the rms level of the
input signal frequency as seen at the output. THD is calcu-
lated as
(SINAD − 1.76) / 6.02 and says that the converter is equiva-
lent to a perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency
at which the reconstructed output fundamental drops 3 dB
below its low frequency value for a full scale input.
GAIN ERROR is the deviation of the last code transition
(111...110) to (111...111) from the ideal (VREF − 1.5 LSB),
after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the
where Af1 is the RMS power of the input frequency at the
output and Af2 through Af6 are the RMS power in the first 5
harmonic frequencies.
deviation of each individual code from a line drawn from
negative full scale (1⁄
2
LSB below the first code transition)
through positive full scale (1⁄
2
LSB above the last code
transition). The deviation of any given code from this straight
line is measured from the center of that code value.
THROUGHPUT TIME is the minimum time required between
the start of two successive conversion. It is the acquisition
time plus the conversion time.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
It is defined as the ratio of the power in the second and third
order intermodulation products to the sum of the power in
both of the original frequencies. IMD is usually expressed in
dB.
7
www.national.com
Typical Performance Characteristics TA = +25˚C, fSAMPLE = 200 ksps to 500 ksps,
fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated.
DNL
INL
fSCLK = 4 MHz
fSCLK = 4 MHz
20144620
20144621
DNL
INL
fSCLK = 10 MHz
fSCLK = 10 MHz
20144660
20144661
DNL vs. Clock Frequency
INL vs. Clock Frequency
20144665
20144666
www.national.com
8
Typical Performance Characteristics TA = +25˚C, fSAMPLE = 200 ksps to 500 ksps,
fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated. (Continued)
SNR vs. Clock Frequency
SINAD vs. Clock Frequency
20144663
20144664
SFDR vs. Clock Frequency
THD vs. Clock Frequency
20144667
20144668
Spectral Response, VA = 5.25V
fSCLK = 4 MHz
Spectral Response, VA = 5.25V
fSCLK = 10 MHz
20144669
20144670
9
www.national.com
Typical Performance Characteristics TA = +25˚C, fSAMPLE = 200 ksps to 500 ksps,
fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated. (Continued)
Power Consumption vs. Throughput,
fSCLK = 10 MHz
20144655
www.national.com
10
Figure 4 shows the device in hold mode: switch SW1 con-
nects the sampling capacitor to ground, maintaining the
sampled voltage, and switch SW2 unbalances the compara-
tor. The control logic then instructs the charge-redistribution
DAC to add or subtract fixed amounts of charge from the
sampling capacitor until the comparator is balanced. When
the comparator is balanced, the digital word supplied to the
DAC is the digital representation of the analog input voltage.
The device moves from hold mode to track mode on the 13th
rising edge of SCLK.
Applications Information
1.0 ADC121S051 OPERATION
The ADC121S051 is a successive-approximation analog-to-
digital converters designed around a charge-redistribution
digital-to-analog converter core. Simplified schematics of the
ADC121S051 in both track and hold modes are shown in
Figure 3 and Figure 4, respectively. In Figure 3, the device is
in track mode: switch SW1 connects the sampling capacitor
to the input, and SW2 balances the comparator inputs. The
device is in this state until CS is brought low, at which point
the device moves to the hold mode.
20144609
FIGURE 3. ADC121S051 in Track Mode
20144610
FIGURE 4. ADC121S051 in Hold Mode
2.0 USING THE ADC121S051
edge of CS. The converter moves from hold mode to track
mode on the 13th rising edge of SCLK (see Figure 2). The
SDATA pin will be placed back into TRI-STATE after the 16th
falling edge of SCLK, or at the rising edge of CS, whichever
occurs first. After a conversion is completed, the quiet time
(tQUIET) must be satisfied before bringing CS low again to
begin another conversion.
The serial interface timing diagram for the ADC121S051 is
shown in Figure 2. CS is chip select, which initiates conver-
sions on the ADC121S051 and frames the serial data trans-
fers. SCLK (serial clock) controls both the conversion pro-
cess and the timing of serial data. SDATA is the serial data
out pin, where a conversion result is found as a serial data
stream.
Sixteen SCLK cycles are required to read a complete
sample from the ADC121S051. The sample bits (including
leading zeroes) are clocked out on falling edges of SCLK,
and are intended to be clocked in by a receiver on subse-
quent falling edges of SCLK. The ADC121S051 will produce
three leading zero bits on SDATA, followed by twelve data
bits, most significant first.
Basic operation of the ADC121S051 begins with CS going
low, which initiates a conversion process and data transfer.
Subsequent rising and falling edges of SCLK will be labelled
with reference to the falling edge of CS; for example, "the
third falling edge of SCLK" shall refer to the third falling edge
of SCLK after CS goes low.
If CS goes low before the rising edge of SCLK, an additional
(fourth) zero bit may be captured by the next falling edge of
SCLK.
At the fall of CS, the SDATA pin comes out of TRI-STATE,
and the converter moves from track mode to hold mode. The
input signal is sampled and held for conversion on the falling
11
www.national.com
5.0 ANALOG INPUTS
Applications Information (Continued)
An equivalent circuit for the ADC121S051’s input is shown in
Figure 7. Diodes D1 and D2 provide ESD protection for the
analog inputs. At no time should the analog input go beyond
(VA + 300 mV) or (GND − 300 mV), as these ESD diodes will
begin conducting, which could result in erratic operation.
3.0 ADC121S051 TRANSFER FUNCTION
The output format of the ADC121S051 is straight binary.
Code transitions occur midway between successive integer
LSB values. The LSB width for the ADC121S051 is VA/4096.
The ideal transfer characteristic is shown in Figure 5. The
transition from an output code of 0000 0000 0000 to a code
of 0000 0000 0001 is at 1/2 LSB, or a voltage of VA/8192.
Other code transitions occur at steps of one LSB.
The capacitor C1 in Figure 7 has a typical value of 4 pF, and
is mainly the package pin capacitance. Resistor R1 is the on
resistance of the track / hold switch, and is typically 500
ohms. Capacitor C2 is the ADC121S051 sampling capacitor
and is typically 26 pF. The ADC121S051 will deliver best
performance when driven by a low-impedance source to
eliminate distortion caused by the charging of the sampling
capacitance. This is especially important when using the
ADC121S051 to sample AC signals. Also important when
sampling dynamic signals is an anti-aliasing filter.
20144614
20144611
FIGURE 7. Equivalent Input Circuit
FIGURE 5. Ideal Transfer Characteristic
6.0 DIGITAL INPUTS AND OUTPUTS
4.0 TYPICAL APPLICATION CIRCUIT
The ADC121S051 digital inputs (SCLK and CS) are not
limited by the same maximum ratings as the analog inputs.
The digital input pins are instead limited to +5.25V with
respect to GND, regardless of VA, the supply voltage. This
allows the ADC121S051 to be interfaced with a wide range
of logic levels, independent of the supply voltage.
A typical application of the ADC121S051 is shown in
Figure 6. Power is provided in this example by the National
Semiconductor LP2950 low-dropout voltage regulator, avail-
able in a variety of fixed and adjustable output voltages. The
power supply pin is bypassed with a capacitor network lo-
cated close to the ADC121S051. Because the reference for
the ADC121S051 is the supply voltage, any noise on the
supply will degrade device noise performance. To keep noise
off the supply, use a dedicated linear regulator for this de-
vice, or provide sufficient decoupling from other circuitry to
keep noise off the ADC121S051 supply pin. Because of the
ADC121S051’s low power requirements, it is also possible to
use a precision reference as a power supply to maximize
performance. The three-wire interface is shown connected to
a microprocessor or DSP.
7.0 MODES OF OPERATION
The ADC121S051 has two possible modes of operation:
normal mode, and shutdown mode. The ADC121S051 en-
ters normal mode (and a conversion process is begun) when
CS is pulled low. The device will enter shutdown mode if CS
is pulled high before the tenth falling edge of SCLK after CS
is pulled low, or will stay in normal mode if CS remains low.
Once in shutdown mode, the device will stay there until CS is
brought low again. By varying the ratio of time spent in the
normal and shutdown modes, a system may trade-off
throughput for power consumption, with a sample rate as low
as zero.
7.1 Normal Mode
The fastest possible throughput is obtained by leaving the
ADC121S051 in normal mode at all times, so there are no
power-up delays. To keep the device in normal mode con-
tinuously, CS must be kept low until after the 10th falling
edge of SCLK after the start of a conversion (remember that
a conversion is initiated by bringing CS low).
If CS is brought high after the 10th falling edge, but before
the 16th falling edge, the device will remain in normal mode,
but the current conversion will be aborted, and SDATA will
return to TRI-STATE (truncating the output word).
20144613
FIGURE 6. Typical Application Circuit
Sixteen SCLK cycles are required to read all of a conversion
word from the device. After sixteen SCLK cycles have
www.national.com
12
To enter shutdown mode, a conversion must be interrupted
by bringing CS high anytime between the second and tenth
falling edges of SCLK, as shown in Figure 8. Once CS has
been brought high in this manner, the device will enter
shutdown mode; the current conversion will be aborted and
SDATA will enter TRI-STATE. If CS is brought high before the
second falling edge of SCLK, the device will not change
mode; this is to avoid accidentally changing mode as a result
of noise on the CS line.
Applications Information (Continued)
elapsed, CS may be idled either high or low until the next
conversion. If CS is idled low, it must be brought high again
before the start of the next conversion, which begins when
CS is again brought low.
After sixteen SCLK cycles, SDATA returns to TRI-STATE.
Another conversion may be started, after tQUIET has
elapsed, by bringing CS low again.
7.2 Shutdown Mode
Shutdown mode is appropriate for applications that either do
not sample continuously, or it is acceptable to trade through-
put for power consumption. When the ADC121S051 is in
shutdown mode, all of the analog circuitry is turned off.
20144616
FIGURE 8. Entering Shutdown Mode
20144617
FIGURE 9. Entering Normal Mode
To exit shutdown mode, bring CS back low. Upon bringing
CS low, the ADC121S051 will begin powering up (power-up
time is specified in the Timing Specifications table). This
power-up delay results in the first conversion result being
unusable. The second conversion performed after power-up,
however, is valid, as shown in Figure 9.
When the VA supply is first applied, the ADC121S051 may
power up in either of the two modes: normal or shutdown. As
such, one dummy conversion should be performed after
start-up, as described in the previous paragraph. The part
may then be placed into either normal mode or the shutdown
mode, as described in Sections 7.1 and 7.2.
If CS is brought back high before the 10th falling edge of
SCLK, the device will return to shutdown mode. This is done
to avoid accidentally entering normal mode as a result of
noise on the CS line. To exit shutdown mode and remain in
normal mode, CS must be kept low until after the 10th falling
edge of SCLK. The ADC121S051 will be fully powered-up
after 16 SCLK cycles.
When the ADC121S051 is operated continuously in normal
mode, the maximum throughput is fSCLK / 20. Throughput
may be traded for power consumption by running fSCLK at its
maximum specified rate and performing fewer conversions
per unit time, raising the ADC121S051 CS line after the 10th
and before the 15th fall of SCLK of each conversion. A plot of
typical power consumption versus throughput is shown in
the Typical Performance Curves section. To calculate the
power consumption for a given throughput, multiply the frac-
tion of time spent in the normal mode by the normal mode
power consumption and add the fraction of time spent in
shutdown mode multiplied by the shutdown mode power
consumption. Note that the curve of power consumption vs.
throughput is essentially linear. This is because the power
consumption in the shutdown mode is so small that it can be
ignored for all practical purposes.
8.0 POWER MANAGEMENT
The ADC121S051 takes time to power-up, either after first
applying VA, or after returning to normal mode from shut-
down mode. This corresponds to one "dummy" conversion
for any SCLK frequency within the specifications in this
document. After this first dummy conversion, the
ADC121S051 will perform conversions properly. Note that
the tQUIET time must still be included between the first
dummy conversion and the second valid conversion.
13
www.national.com
noise in the substrate that will degrade noise performance if
that current is large enough. The larger the output capaci-
tance, the more current flows through the die substrate and
the greater is the noise coupled into the analog channel,
degrading noise performance.
Applications Information (Continued)
9.0 POWER SUPPLY NOISE CONSIDERATIONS
The charging of any output load capacitance requires cur-
rent from the power supply, VA. The current pulses required
from the supply to charge the output capacitance will cause
voltage variations on the supply. If these variations are large
enough, they could degrade SNR and SINAD performance
of the ADC. Furthermore, discharging the output capaci-
tance when the digital output goes from a logic high to a logic
low will dump current into the die substrate, which is resis-
tive. Load discharge currents will cause "ground bounce"
To keep noise out of the power supply, keep the output load
capacitance as small as practical. It is good practice to use a
100 Ω series resistor at the ADC output, located as close to
the ADC output pin as practical. This will limit the charge and
discharge current of the output capacitance and improve
noise performance.
www.national.com
14
Physical Dimensions inches (millimeters) unless otherwise noted
6-Lead LLP
Order Number ADC121S051CISD or ADC121S051CISDX
NS Package Number SDB06A
6-Lead SOT-23
Order Number ADC121S051CIMF, ADC121S051CIMFX
NS Package Number MF06A
15
www.national.com
Notes
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.
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 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.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
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.
Leadfree products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
National Semiconductor
Asia Pacific Customer
Support Center
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
Email: ap.support@nsc.com
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
相关型号：
ADC121S101CIMF/NOPB
IC 1-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDSO6, SOT-23, 6 PIN, Analog to Digital Converter
NSC
©2020 ICPDF网 联系我们和版权申明