ADS5221PFBR [TI]

12-Bit, 65MSPS Sampling, +3.3V ANALOG-TO-DIGITAL CONVERTER; 12位, 65MSPS采样, + 3.3V模拟数字转换器
ADS5221PFBR
型号: ADS5221PFBR
厂家: TEXAS INSTRUMENTS    TEXAS INSTRUMENTS
描述:

12-Bit, 65MSPS Sampling, +3.3V ANALOG-TO-DIGITAL CONVERTER
12位, 65MSPS采样, + 3.3V模拟数字转换器

转换器
文件: 总19页 (文件大小:365K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
ADS5221  
ADS5221  
SBAS262A – APRIL 2003 – REVISED DECEMBER 2003  
12-Bit, 65MSPS Sampling, +3.3V  
ANALOG-TO-DIGITAL CONVERTER  
FEATURES  
DESCRIPTION  
HIGH SNR: 70dB  
The ADS5221 is a pipeline, CMOS Analog-to-Digital Con-  
verter (ADC) that operates from a single +3.3V power  
supply. This converter provides excellent performance with a  
single-ended input and can be operated with a differential  
input for added spurious performance. This high-perfor-  
mance converter includes a 12-bit quantizer, high bandwidth  
track-and-hold, and a high accuracy internal reference; it  
also allows for the user to disable the internal reference and  
utilize external references, providing excellent gain and off-  
set matching in multi-channel applications or in applications  
where full-scale range adjustment is required.  
HIGH SFDR: 88dBFS  
LOW POWER: 285mW  
INTERNAL/EXTERNAL REFERENCE OPTION  
SINGLE-ENDED OR  
FULLY DIFFERENTIAL ANALOG INPUT  
FLEXIBLE DUTY CYCLE ADJUST CIRCUITRY  
LOW DNL: 0.5LSB  
SINGLE +3.3V SUPPLY OPERATION  
TQFP-48  
The ADS5221 employs digital error correction techniques to  
enable excellent differential linearity for demanding imaging  
applications. Its low distortion and high SNR give the extra  
margin needed for medical imaging, communications, video,  
and test instrumentation. The ADS5221 offers power dissi-  
pation of 285mW and also provides two power-down modes.  
APPLICATIONS  
WIRELESS LOCAL LOOP  
COMMUNICATIONS  
The ADS5221 is specified at a maximum sampling fre-  
quency of 65MHz and a differential input range of 1V to 2V.  
The ADS5221 is available in a TQFP-48.  
MEDICAL IMAGING  
PORTABLE INSTRUMENTATION  
AVDD  
CLK  
VDRV  
ADS5221  
Timing/Duty Cycle  
Adjust  
Circuitry  
IN  
D0  
12-Bit  
Pipelined  
ADC  
Error  
Correction  
Logic  
3-State  
Output  
VIN  
S/H  
D11  
IN  
OVR  
Internal  
Reference  
STPD QPD  
REFT REFB  
RSEL VREF  
OE  
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of  
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.  
All trademarks are the property of their respective owners.  
PRODUCTION DATA information is current as of publication date.  
Products conform to specifications per the terms of Texas Instruments  
standard warranty. Production processing does not necessarily include  
testing of all parameters.  
Copyright © 2003, Texas Instruments Incorporated  
www.ti.com  
ABSOLUTE MAXIMUM RATINGS(1)  
ELECTROSTATIC  
DISCHARGE SENSITIVITY  
This integrated circuit can be damaged by ESD. Texas Instru-  
ments recommends that all integrated circuits be handled with  
appropriate precautions. Failure to observe proper handling  
and installation procedures can cause damage.  
AVDD, DVDD, VDRV .......................................................................... +3.8V  
Analog Input ........................................................... 0.3V to (AVDD + 0.3V)  
Logic Input ............................................................. 0.3V to (AVDD + 0.3V)  
Case Temperature ......................................................................... +100°C  
Junction Temperature .................................................................... +150°C  
Storage Temperature ..................................................................... +150°C  
NOTE: (1) Stresses above these ratings may cause permanent damage.  
Exposure to absolute maximum conditions for extended periods may degrade  
device reliability.  
ESD damage can range from subtle performance degradation  
tocompletedevicefailure. Precisionintegratedcircuitsmaybe  
more susceptible to damage because very small parametric  
changes could cause the device not to meet its published  
specifications.  
PACKAGE/ORDERING INFORMATION(1)  
SPECIFIED  
PACKAGE  
DESIGNATOR  
TEMPERATURE  
RANGE  
PACKAGE  
MARKING  
ORDERING  
NUMBER  
TRANSPORT  
MEDIA, QUANTITY  
PRODUCT  
PACKAGE-LEAD  
ADS5221  
"
TQFP-48  
"
PFB  
"
40°C to +85°C  
ADS5221PFB  
"
ADS5221PFBT  
ADS5221PFBR  
Tape and Reel, 250  
Tape and Reel, 2000  
"
ADS5221  
"
QFN-48(2)  
"
RGZ  
"
40°C to +85°C  
ADS5221RGZ  
"
ADS5221RGZ  
ADS5221RGZR  
Rails, 52  
Tape and Reel, 1000  
"
NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet.  
(2) This package available beginning Q1 2004.  
ELECTRICAL CHARACTERISTICS: AVDD = 3.3V  
TMIN = 40°C, TMAX = +85°C, typical values are at TA = +25°C, sampling rate = 65MSPS, 50% clock duty cycle, AVDD = 3.3V, VDRV = 2.5V, 1dBFS, internal reference  
voltage, and 2VPP differential input, unless otherwise noted.  
ADS5221  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
RESOLUTION  
12 Tested  
Bits  
SPECIFIED TEMPERATURE RANGE  
Ambient Air  
40 to +85  
°C  
ANALOG INPUT  
Single-Ended Input Range  
Optional Single-Ended Input Range  
Differential Input Range  
Analog Input Bias Current  
Input Impedance  
2VPP  
1VPP  
2VPP  
0.5  
1
1
2.5  
2
2
V
V
V
1
µA  
M|| pF  
MHz  
Static, No Clock  
3dBFS Input  
1.25 || 5  
300  
Analog Input Bandwidth  
CONVERSION CHARACTERISTICS  
Sample Rate  
1M  
65M  
Samples/s  
Data Latency  
5
Clock Cycle  
DYNAMIC CHARACTERISTICS  
Differential Linearity Error (largest code error)  
f = 2.4MHz  
f = 9.7MHz  
No Missing Codes  
Integral Nonlinearity Error, f = 2.4MHz  
Spurious-Free Dynamic Range(1)  
f = 2.4MHz  
f = 9.7MHz  
f = 32.5MHz  
±0.3  
±0.5  
Tested  
±0.5  
±0.75  
±1.75  
LSB  
LSB  
LSBs  
Referred to Full-Scale  
90  
88  
85  
dBFS(2)  
dBFS  
dBFS  
at 25°C  
78  
2-Tone Intermodulation Distortion(3)  
f = 9.5MHz and 10.5MHz (7dB each tone)  
Signal-to-Noise Ratio (SNR)  
f = 2.4MHz  
f = 9.7MHz  
f = 32.5MHz  
Signal-to-(Noise + Distortion) (SINAD)  
f = 2.4MHz  
f = 9.7MHz  
92  
dBFS  
Referred to Full-Scale  
at 25°C  
70  
70  
69  
dB  
dB  
dB  
68  
67  
Referred to Full-Scale  
at 25°C  
70  
70  
dB  
dB  
f = 32.5MHz  
68  
dB  
Bits  
Effective Number of Bits(4), f = 2.4MHz  
Output Noise  
11.2  
0.2  
3.0  
1.2  
1.0  
5
Input Tied to Common-Mode  
LSBs rms  
ns  
ps rms  
Clock Cycle  
ns  
Aperture Delay Time  
Aperture Jitter  
Over-Voltage Recovery Time  
Full-Scale Step Acquisition Time  
ADS5221  
2
SBAS262A  
www.ti.com  
ELECTRICAL CHARACTERISTICS: AVDD = 3.3V (Cont.)  
TMIN = 40°C, TMAX = +85°C, typical values are at TA = +25°C, sampling rate = 65MSPS, 50% clock duty cycle, AVDD = 3.3V, VDRV = 2.5V, 1dBFS, internal reference  
voltage, and 2VPP differential input, unless otherwise noted.  
ADS5221  
PARAMETER  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
DIGITAL INPUTS  
Logic Family  
CMOS-Compatible  
Rising Edge of Convert Clock  
100  
Convert Command  
Start Conversion  
High Level Input Current(5) (VIN = 3VDD  
Low Level Input Current (VIN = 0V)  
High Level Input Voltage  
Low Level Input Voltage  
Input Capacitance  
)
µA  
µA  
V
V
pF  
10  
+1.7  
+0.7  
5
DIGITAL OUTPUTS  
Logic Family  
Logic Coding  
Low Output Voltage (IOL = 50µA to 1.5mA)  
High Output Voltage (IOH = 50µA to 0.5mA)  
3-State Enable Time  
CMOS-Compatible  
Straight Offset Binary or BTC  
+0.1  
VDRV = 2.5V  
V
V
+2.4  
OE = H  
OE = L  
20  
2
40  
10  
ns  
ns  
pF  
3-State Disable Time  
Output Capacitance  
5
ACCURACY (Internal Reference, 2VPP  
Unless Otherwise Noted)  
Zero Error (referred to midscale)  
Zero Error Drift (referred to midscale)  
Gain Error(6)  
Gain Error Drift(6)  
,
fIN = 2.4MHz, at 25°C  
fIN = 9.7MHz, at 25°C  
AVDD = ±5%  
±0.5  
5
±0.4  
38  
±1.5  
±35  
%FS  
ppm/°C  
%FS  
ppm/°C  
dB  
Power-Supply Rejection of Gain  
56  
INTERNAL VOLTAGE REFERENCE  
Output Voltage Error (1V)  
Load Regulation at 1.0mA  
Output Voltage Error (0.5V)  
Load Regulation at 0.5mA  
±5  
0.8  
±2.5  
0.1  
mV  
mV  
mV  
mV  
POWER-SUPPLY REQUIREMENTS  
Supply Voltage: AVDD, DVDD  
Driver Supply Voltage: VDRV  
Supply Current: +IS  
Power Dissipation: VDRV = 2.5V  
VDRV = 3.3V  
Operating  
+3.0  
+2.3  
+3.3  
+2.5  
86  
285  
290  
15  
+3.6  
+3.6  
V
V
Operating (External Reference)  
mA  
mW  
mW  
mW  
mW  
295  
Standard Power-Down  
Quasi Power-Down  
70  
Thermal Resistance, θJA  
TQFP-48  
QFN-48  
63.7  
26.1  
°C/W  
°C/W  
NOTES: (1) Spurious-Free Dynamic Range refers to the magnitude of the largest harmonic.  
(2) dBFS means dB relative to Full-Scale.  
(3) 2-tone intermodulation distortion is referred to the largest fundamental tone. This number will be 6dB higher if it is referred to the magnitude of the  
2-tone fundamental envelope.  
(4) Effective Number of Bits (ENOB) is defined by (SINAD 1.76)/6.02.  
(5) A 50kpull-down resistor is inserted internally on the OE pin.  
(6) Includes internal reference.  
ADS5221  
SBAS262A  
3
www.ti.com  
PIN CONFIGURATION  
48 47 46 45 44 43 42 41 40 39 38 37  
MSBI  
OE  
1
2
3
4
5
6
7
8
9
36 AVDD  
35 NC  
Mode Select  
STPD  
34 REFT  
33 NC  
QPD  
32 REFB  
31 RSEL  
30 VREF  
29 AGND  
28 AGND  
27 AGND  
26 NC  
GDRV  
ADS5221  
GDRV  
VDRV  
VDRV  
D11 (MSB) 10  
D10 11  
D9 12  
25 NC  
13 14 15 16 17 18 19 20 21 22 23 24  
PIN ASSIGNMENTS  
PIN  
I/O  
NAME  
DESCRIPTION  
PIN  
I/O  
NAME  
DESCRIPTION  
1
MSBI  
Most Significant Bit Invert (HI = Binary Twos  
Complement, LO = Straight Offset Binary)  
Tri-State (LO = Enabled, HI = Tri-State)  
25  
26  
27  
28  
29  
30  
NC  
No Internal Connection  
No Internal Connection  
Analog Ground  
NC  
2
3
OE  
AGND  
AGND  
AGND  
VREF  
Mode Select Duty Cycle Adjust (HI = Enabled,  
LO = Normal Operation)  
Analog Ground  
Analog Ground  
4
5
STPD  
Standard Power-Down (LO = Normal  
Operation, HI = Enabled)  
Internal Reference Voltage  
(1/2V Reference)  
QPD  
Quasi Power-Down (LO = Normal Operation,  
HI = Enabled)  
31  
RSEL  
Reference Mode Select (see Table I for  
settings)  
6
GDRV  
GDRV  
VDRV  
VDRV  
D11 (MSB)  
D10  
Output Driver Ground  
7
Output Driver Ground  
32  
33  
34  
35  
36  
37  
38  
39  
40  
41  
42  
43  
44  
45  
46  
47  
48  
REFB  
NC  
Bottom Reference Bypass  
8
Output Driver Supply  
No Internal Connection  
Top Reference Bypass  
No Internal Connection  
Analog Supply  
9
Output Driver Supply  
REFT  
NC  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
O
O
O
O
O
O
O
O
O
O
O
O
Data Bit 12  
Data Bit 11  
AVDD  
AVDD  
AGND  
AGND  
AGND  
IN  
D9  
Data Bit 10  
Analog Supply  
D8  
Data Bit 9  
Analog Ground  
D7  
Data Bit 8  
Analog Ground  
D6  
Data Bit 7  
Analog Ground  
D5  
Data Bit 6  
I
I
Analog Input  
D4  
Data Bit 5  
IN  
Complementary Analog Input  
Analog Ground  
D3  
Data Bit 4  
AGND  
DGND  
DGND  
CLK  
D2  
Data Bit 3  
Digital Ground  
D1  
Data Bit 2  
Digital Ground  
D0 (LSB)  
NC  
Data Bit 1  
I
I
I
Convert Clock Input  
Digital Supply  
No Internal Connection  
No Internal Connection  
Over-Range Indicator  
DVDD  
DVDD  
NC  
Digital Supply  
OVR  
ADS5221  
4
SBAS262A  
www.ti.com  
TIMING DIAGRAM  
N + 2  
N + 1  
N + 4  
N + 3  
Analog In  
N + 7  
N + 5  
N
N + 6  
tL  
tH  
tD  
tCONV  
Clock  
5 Clock Cycles  
t2  
Data Out  
N 5  
N 4  
N 3  
N 2  
N 1  
N
N + 1  
N + 2  
Data Invalid  
t1  
SYMBOL  
DESCRIPTION  
MIN  
TYP  
MAX  
UNITS  
tCONV  
tL  
tH  
tD  
t1  
Convert Clock Period  
Clock Pulse LOW  
Clock Pulse HIGH  
Aperture Delay  
15.4ns  
6.7  
6.7  
100µs  
7.7  
7.7  
3
ns  
ns  
ns  
ns  
ns  
Data Hold Time, CL = 0pF  
Propagation Delay Time, CL = 5pF max  
6.0  
t2  
6.5  
ADS5221  
SBAS262A  
5
www.ti.com  
TYPICAL CHARACTERISTICS: AVDD = 3.3V  
TMIN = 40°C, TMAX = +85°C, typical values are at TA = +25°C, sampling rate = 65MSPS, 50% clock duty cycle, AVDD = 3.3V, VDRV = 2.5V, 1dBFS, internal reference  
voltage, and 2VPP differential input, unless otherwise noted.  
SPECTRAL PERFORMANCE  
(Differential, 2VPP  
SPECTRAL PERFORMANCE  
(Differential, 2VPP  
)
)
0
20  
0
20  
fIN = 2.4MHz (1dBFS)  
SFDR = 90.2dBFS  
SNR = 70.2dBFS  
fIN = 9.7MHz (1dBFS)  
SFDR = 90.1dBFS  
SNR = 70.1dBFS  
SINAD = 70.1dBFS  
SINAD = 69.9dBFS  
40  
40  
60  
60  
80  
80  
100  
120  
100  
120  
0
0
0
6.5  
13  
26  
32.5  
0
0
0
6.5  
13  
26  
32.5  
Frequency (MHz)  
Frequency (MHz)  
SPECTRAL PERFORMANCE  
(Differential, 2VPP, External Reference)  
SPECTRAL PERFORMANCE  
(Differential, 1VPP  
)
0
20  
0
20  
fIN = 9.7MHz (1dBFS)  
fIN = 2.4MHz (1dBFS)  
SFDR = 89.3dBFS  
SNR = 66.9dBFS  
SFDR = 89.3dBFS  
SNR = 69.3dBFS  
SINAD = 69.2dBFS  
SINAD = 66.9dBFS  
40  
40  
60  
60  
80  
80  
100  
120  
100  
120  
6.5  
13  
26  
6.5  
13  
26  
32.5  
32.5  
Frequency (MHz)  
Frequency (MHz)  
SPECTRAL PERFORMANCE  
(Single-Ended, 2VPP  
)
TWO TONE INTERMODULATION DISTORTION  
0
20  
0
20  
40  
40  
60  
60  
80  
80  
100  
120  
100  
120  
6.5  
13  
26  
32.5  
6.5  
13  
Frequency (MHz)  
26  
32.5  
Frequency (MHz)  
ADS5221  
6
SBAS262A  
www.ti.com  
TYPICAL CHARACTERISTICS: AVDD = 3.3V (Cont.)  
TMIN = 40°C, TMAX = +85°C, typical values are at TA = +25°C, sampling rate = 65MSPS, 50% clock duty cycle, AVDD = 3.3V, VDRV = 2.5V, 1dBFS, internal reference  
voltage, and 2VPP differential input, unless otherwise noted.  
DIFFERENTIAL LINEARITY ERROR  
TWO-TONE INTERMODULATION DISTORTION  
EXTERNAL REFERENCE  
0
20  
1.0  
0.8  
fIN = 9.7MHz  
0.6  
0.4  
40  
0.2  
60  
0
0.2  
0.4  
0.6  
0.8  
1.0  
80  
100  
120  
0
0
0
6.5  
13  
26  
32.5  
0
1024  
2048  
Code  
3072  
4096  
Frequency (MHz)  
DIFFERENTIAL LINEARITY ERROR  
INTEGRAL LINEARITY ERROR  
1.0  
0.8  
1.0  
0.8  
f
IN = 9.7MHz  
0.6  
0.6  
0.4  
0.4  
0.2  
0.2  
0
0
0.2  
0.4  
0.6  
0.8  
1.0  
0.2  
0.4  
0.6  
0.8  
1.0  
1024  
2048  
Code  
3072  
4096  
0
1024  
2048  
Code  
3072  
4096  
INTEGRAL LINEARITY ERROR  
EXTERNAL REFERENCE  
SWEPT POWER (SNR)  
dBFS  
80  
70  
60  
50  
40  
30  
20  
10  
0
1.0  
0.8  
fIN = 9.7MHz  
0.6  
0.4  
0.2  
dBc  
0
0.2  
0.4  
0.6  
0.8  
1.0  
70  
60  
50  
40  
30  
20  
10  
0
1024  
2048  
Code  
3072  
4096  
Analog Input Level (dBFS)  
ADS5221  
SBAS262A  
7
www.ti.com  
TYPICAL CHARACTERISTICS: AVDD = 3.3V (Cont.)  
TMIN = 40°C, TMAX = +85°C, typical values are at TA = +25°C, sampling rate = 65MSPS, 50% clock duty cycle, AVDD = 3.3V, VDRV = 2.5V, 1dBFS, internal reference  
voltage, and 2VPP differential input, unless otherwise noted.  
SWEPT POWER (SNR)  
SWEPT POWER (SFDR)  
fIN = 9.7MHz  
(External Reference)  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
80  
70  
60  
50  
40  
30  
20  
10  
0
fIN = 9.7MHz  
dBFS  
dBFS  
dBc  
dBc  
80  
70  
60  
50  
40  
30  
20  
10  
0
70  
60  
50  
40  
30  
20  
10  
0
Analog Input Level (dBFS)  
Analog Input Level (dBFS)  
SWEPT POWER (SFDR)  
(External Reference)  
DYNAMIC PERFORMANCE vs INPUT FREQUENCY  
SFDR  
100  
90  
80  
70  
60  
50  
40  
30  
20  
10  
0
95  
90  
85  
80  
75  
70  
65  
60  
55  
50  
45  
fIN = 9.7MHz  
dBc  
dBFS  
SNR  
80  
70  
60  
50  
40  
30  
20  
10  
0
1
10  
100  
Analog Input Level (dBFS)  
Frequency (MHz)  
POWER DISSIPATION vs INPUT FREQUENCY  
320  
305  
290  
275  
260  
245  
230  
215  
200  
1
10  
100  
Frequency (MHz)  
ADS5221  
8
SBAS262A  
www.ti.com  
ANALOG INPUT  
APPLICATION INFORMATION  
Depending on the application and the desired level of perfor-  
mance , the analog input of the ADS5221 can be configured  
in various ways and driven with different circuits. The ADS5221  
is particularly well-suited for communication systems that  
digitize large scale and wideband signals. In any case, the  
analog interface requirements should be carefully examined  
before selecting the appropriate circuit configuration. The  
circuit definition should include considerations on the input  
frequency band and amplitude, as well as the available  
power supplies.  
THEORY OF OPERATION  
The ADS5221 is a 12-bit, 65MSPS, CMOS ADC designed  
with a fully differential pipeline architecture. The pipeline  
consists of three sections: a 3-bit quantizer, eight middle  
stages with a 1.5-bit quantizer for each stage, and a 4-bit  
flash. The output of each pipeline stage is processed and  
formed into 12-bit data in the digital error correction logic  
section to ensure good differential linearity of the ADC. The  
converter includes a high bandwidth track-and-hold amplifier  
in the input stage as shown in Figure 1. It provides excellent  
performance for a single-ended input or differential input of IF  
(Intermediate Frequency) or an under-sampling signal. The  
rising edge of the input clock initiates the conversion pro-  
cess. Once the signal is captured by the input track-and-hold,  
the bits are sequentially encoded starting with the Most  
Significant Bit (MSB). This process results in a data latency  
of 5 clock cycles. The ADS5221 includes a high accuracy  
internal reference and also allows to the use of an external  
reference. The input full-scale range is up to +2V and is  
selectable based on the reference voltage setting. For nor-  
mal operation, both analog inputs (IN, IN) require external  
common-mode voltage as signal swing center. The output  
data of ADS5221 is available as a 12-bit parallel word either  
coded in a Straight Offset Binary or Binary Twos Comple-  
ment format. The ADS5221 includes an option of a duty cycle  
stabilizer (DCS) that allows ADS5221 to operate with a non-  
square wave input clock, such as from a 30% to 70% duty  
cycle. When the DCS is selected the ADS5221 maintains an  
internal clock duty cycle at 50% with ±5% tolerance. The  
ADS5221 has low power dissipation in normal mode and has  
two power down modes for energy saving. The device  
operates from a single +3.3V power supply and has a  
separate digital output driver supply pin.  
INPUT IMPEDANCE  
The input impedance of the ADS5221 is capacitive due to the  
input stray and sampling capacitors. These capacitors effec-  
tively result in a dynamic input impedance that is a function  
of the sampling and input frequency. Figure 2 depicts the  
differential input impedance of the ADS5221 as a function of  
the signal input frequency. At certain sampling rates, increas-  
ing the signal frequency will decrease the input impedance.  
This factor needs to be considered when the signal source is  
designed. For applications that use op amps to drive the  
ADC, it is recommended that a series resistor be added  
between the amplifier output and the converter inputs. This  
will isolate the capacitive input of the converter from the  
driving source and avoid gain peaking, or instability; further-  
more, it will create a 1st-order, low-pass filter (LPF) in  
conjunction with the specified input capacitance of the  
ADS5221. The cutoff frequency of this LPF can be further  
adjusted by adding an external shunt capacitor from each  
signal input to ground. In any case, the use of the RC  
network is optional, but optimizing the values to adapt to the  
specific application is encouraged.  
DIFFERENTIAL INPUT IMPEDANCE  
50  
S5  
40  
30  
20  
10  
0
S3  
VBIAS  
CIN  
CIN  
S1  
S2  
IN  
IN  
T&H  
S4  
VBIAS  
S6  
1
10  
100  
Input Frequency (MHz)  
Tracking Phase: S1, S2, S3, S4 closed; S5, S6 open  
Hold Phase: S1, S2, S3, S4 open; S5, S6 closed  
FIGURE 2. Differential Input Impedance vs Input Frequency.  
FIGURE1.SimplifiedCircuitofInputTrack-and-HoldAmplifier  
of ADS5221.  
ADS5221  
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INPUT COMMON-MODE VOLTAGE  
ANALOG INPUT DRIVEN BY TRANSFORMER  
The ADS5221 operates from a single +3.3V supply, and  
requires a external common-mode voltage. This allows a  
symmetrical signal swing while maintaining sufficient head-  
room to the supply rail. The common-mode voltage can be  
from an external DC voltage source, for example, an analog  
+3.3V supply with a simple resister divider, or from the input  
signal source with DC-coupling. When it is a single-ended  
input configuration, the common-mode voltage is typically  
+1.25V. When the input configuration is differential, the  
common-mode voltage is +1.5V.  
The ADS5221 can be driven by a transformer, which pro-  
vides signal AC-coupling and allows a signal conversion from  
single-ended input to differential output, or from single-ended  
input to single-ended output. Using a transformer offers a  
number of advantages. As a passive component, it does not  
add to the total noise and has better harmonics in wide  
frequency bands, compared to an op amp driver. By using a  
step-up transformer, further signal amplification can be real-  
ized; as a result, the signal swing from the source can be  
reduced. For transformer selection, it is important to carefully  
examine the application requirements and determine the  
correct model, the desired impedance ratio, and frequency  
characteristics. Furthermore, the appropriate model must  
support the targeted distortion level and should not exhibit  
any core saturation at full-scale voltage levels. A variety of  
miniature RF transformers from different manufacturers, (such  
as, Mini-Circuits, Coilcraft, or Trak) can be selected.  
INPUT FULL SCALE RANGE  
The input full-scale range (FSR) of the ADS5221 is select-  
able from +1V to +2V and any value within this range, by  
setting the reference select pin RSEL and reference voltage  
pin VREF (see Table I). The input FSR (differential) is always  
twice VREF (the voltage at the VREF pin) for all reference  
modes.  
Figure 3 shows a transformer-coupled input configuration of  
the ADS5221. The ADS5221 receives a differential AC signal  
from the output of the transformer and common-mode volt-  
age of +1.5V from the center tap. A source termination  
resistor, RT , is required, which can be placed at the input or  
output of the transformer to satisfy the termination require-  
ments of the source impedance, RS. The circuit also shows  
the use of an additional RC low-pass filter placed in series  
with each converter input to attenuate some of the wideband  
noise. The resistor values are typically in the range of 10to  
50, and capacitors are in the range of 10pF to 100pF for  
individual application requirements.  
By choosing different signal input ranges, trade-offs can be  
made between noise and distortion performance. For maxi-  
mizing SNR, the maximum signal input 2VPP range may be  
selected. This range may also be selected for low-level  
(6dBFS to 40dBFS) but high-frequency multi-tone input.  
The signal distortion at the output of the device could be  
sensitive to the input signal with large full-scale. Reducing  
signal amplitude will improve the distortion performance. The  
large input signal amplitude of the converter will impose  
additional design constraints to the op amp due to its head-  
room requirements when the op amp is from single-supply  
and DC-coupling.  
DIFFERENTIAL INPUTS  
The ADS5221 input structure is designed to accept both a  
single-end or differential analog signal. Distortion perfor-  
mance, however, can be improved by utilizing the differential  
input configuration. Differential operation of the ADS5221  
requires that an input signal at the inputs (IN, IN) has the  
same amplitude and is 180 degrees out-of-phase. Differen-  
tial signals offer a number of advantages:  
24.9  
24.9Ω  
T4-6T  
IN  
IN  
ADS5221  
22pF  
RS  
RT  
0.1µF  
AVDD  
The signal amplitude is half that required for the single-  
ended operation, and is therefore less demanding to achieve,  
while maintaining good linearity performance from the  
signal source.  
1.7kΩ  
1.5kΩ  
1.5V  
3.3V  
The reduced signal swing allows for more headroom of the  
interface circuitry, and therefore also allows a wider selec-  
tion of the best suitable driver amplifier.  
FIGURE 3. Transformer-Coupled Differential Input Configura-  
tion of ADS5221.  
Minimization of even-order harmonics.  
Improved noise immunity based on the common-mode  
input rejection of the converter.  
ADS5221  
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ANALOG INPUT DRIVEN BY OP AMPLIFIER  
As shown in Figure 5, an AC-coupled, single-ended input  
configuration is realized with TIs OPA695 for wideband  
applications. For narrowband applications, the OPA2822 can  
be used. In Figure 5, the OPA695 is configured at single  
supply +5V and noninverting operation. The AC gain of the  
amplifier is 2 and the DC offset of the amplifier is +2.5V, set  
by the voltage divider from the op amp power supply. The  
output of the amplifier can provide maximum full-scale volt-  
age range for the ADS5221. The OPA695 is a very high  
bandwidth, current-feedback op amp that combines 4200V/  
µs slew rate and low input voltage noise. It is optimized for  
high gain operation. Further details of the OPA695 can be  
found in the OPA695 data sheet. The common-mode voltage  
at the ADS5221 input is +1.25V, set by a voltage divider from  
+3.3V power supply. The +3.3V power supply must be  
decoupled, as shown in Figure 11.  
The ADS5221 can be driven by an operational amplifier with  
DC or AC signal coupling, as shown in Figure 4 and Figure  
5. In Figure 4, the THS4503, a differential amplifier, is used  
to convert a single-ended input to differential output with a  
gain of 2. The THS4503 provides an output common-mode  
voltage set by VOCM pin, and is DC-coupled to the input of  
ADS5221. A low-pass filter can be created by adding small  
capacitors (for example, 10pF) in parallel with the feedback  
resistors of the THS4503 as needed for some applications.  
Due to the THS4503 driving a capacitive load, small series  
resistors in the output ensure stable operation. Further de-  
tails of this and other functions of the THS4503 may be found  
in its product datasheet, located on the Texas Instruments  
web site (www.ti.com). In general, differential amplifiers pro-  
vide a higher performance driver solution as compared to a  
single-ended amplifier.  
10pF(1)  
+5V  
392  
187Ω  
24.9Ω  
IN  
ADS5221  
VCM  
THS4503  
22pF  
50Ω  
60.4Ω  
24.9Ω  
IN  
0.1µF  
392Ω  
215Ω  
10pF(1)  
AVDD  
5V  
1.7kΩ  
1.5kΩ  
1.5V  
3.3V  
FIGURE 4. Using the THS4503 Differential Amplifier (Gain = 2) to Drive the ADS5221 in a DC-Coupled Configuration.  
+5V  
0.1µF  
6.8µF  
+5V  
1.6kΩ  
1kΩ  
806Ω  
3.3V  
0.1µF  
0.1µF  
30Ω  
806Ω  
487Ω  
IN  
IN  
OPA695  
50Ω  
57.6Ω  
47pF  
47pF  
ADS5221  
0.1µF  
487Ω  
0.1µF  
AVDD  
1.6kΩ  
1kΩ  
1.25V  
3.3V  
FIGURE 5. Single-Ended Input of ADS5221 Driven by OPA695 with Gain = 2.  
ADS5221  
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CLOCK INPUT  
Here, the tJA is the rms aperture jitter from all jitter sources,  
such as clock edge, input signal and the device. The fIN is  
input frequency. The crystal oscillator has very low jitter, but  
if using a clock conditioning circuit (gate, divider, logic lever  
converter, and so forth), an extra jitter and timing variation  
must be limited. In addition, the input clock is treated as an  
analog signal and its power supply should be separated from  
the power supply of the digital output driver to limit the digital  
noise.  
The clock input of the ADS5221 is designed to receive a  
single-ended pulse clock with CMOS/TTL level and DC-  
coupling. There is no external common-mode voltage re-  
quirement at the clock input pin (see Figure 6). The typical  
tolerance of the internal clock duty cycle is ±5% at its nominal  
value of 50% in order to maintain the high performance of the  
device.  
The ADS5221 contains an optional clock duty cycle adjust  
(DCA). When the DCA is enabled (Mode Select = high), a  
wide range of input clock duty cycle can be adjusted inter-  
nally to 50% (±5% tolerance) by correcting the non-sampling  
edge of the clock. In this case, the noise and distortion  
performance will not be affected by the input clock duty cycle  
within this range. When the DCA is disabled (Mode Select =  
low), a clock duty cycle variation greater than ±5% will  
degrade the dynamic performance of the device. In this case,  
an input clock duty cycle less than 45% will automatically  
request a reduction in the sampling rate in order to maintain  
the track/hold period within the specified values for stable  
performance. The DCA disabled mode is suitable for non-  
uniform sampling ADC applications.  
MINIMUM SAMPLING RATE  
The pipeline architecture of the ADS5221 uses a switched-  
capacitor technique in its internal track-and-hold stages. The  
high sampling speed necessitates the use of very small  
capacitor values. In order to hold the droop errors low, the  
capacitors require a minimum refresh rate. To maintain  
accuracy of the acquired sample charge, the sampling clock  
on the ADS5221 must not drop below the specified minimum  
of 1MHz.  
REFERENCE  
ADS5221 provides both internal reference and external ref-  
erence modes by setting pins RSEL and VREF (see Table 1).  
The input full-scale range (FSR) of ADS5221 is always twice  
the voltage VREF at the VREF pin. The REFT and REFB are  
internally buffered, and drive the ADC core for both the  
external reference and internal reference modes. The REFT  
and REFB are designed for external by pass only. The output  
resistance between the REFT and REFB pins is approxi-  
mately 1. When the internal reference mode is selected the  
voltage at VREF is generated by an internal 0.5V bandgap  
voltage through a VREF amplifier, and the VREF output can  
supply 2.5mA source current. When the external reference is  
selected, the internal VREF amplifier is powered down, the  
external reference voltage is added at the VREF pin, and the  
voltage is input to the internal REFT/REFB amplifier. The  
voltage at pins REFT, REFB and VREF, the full scale range  
(FSR) voltage at analog input for both external and internal  
reference modes, and the differential/single-ended input  
configurations are as follows:  
CMOS/TTL  
CLK  
Clock Source  
ADS5221  
50  
50Ω  
FIGURE 6. General Input Clock Interface of ADS5221.  
In any case, a very low jitter clock is fundamental to preserv-  
ing the excellent AC performance of the ADS5221. The  
device itself is specified for a low jitter, characterizing the  
outstanding capability of the internal clock and track-and-  
hold circuitry. Generally, as input frequency increases, clock  
jitter becomes more critical to maintain a good signal-to-  
noise ratio. The following equation can be used to calculate  
the achievable SNR for a given input frequency and clock  
jitter (tJA in ps rms):  
VREFT = VREF/2 +1.5V  
VREFB = 1.5V VREF/2  
VREF = VREFT VREFB  
FSR (Differential) = 2 VREF  
SNR = 20 log [1/(2 π fIN tJA)]  
RSEL PIN  
INPUT FSR (V)  
SELECTED MODE  
CONNECT TO  
VREF PIN (V)  
(Differential)  
REFT (V)  
REFB (V)  
Internal Fixed  
Internal Fixed  
Internal Program  
External  
GND to 0.2V  
VREF Pin  
0.2V to VREF  
AVDD (3.3V)  
1.0  
0.5  
2
1
2
1.75  
VREF/2 + 1.5  
VREF/2 + 1.5  
1
1.25  
1.5 VREF/2  
1.5 VREF/2  
0.5 (1+R2/R1)  
Ext. 0.5V to 1V  
2 VREF  
2 VREF  
TABLE I. Reference Configuration.  
ADS5221  
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The ADS5221 requires solid bypassing for all reference pins  
to keep the effects of clock feedthrough to a minimum and to  
achieve the specified levels of performance. Figure 7 to  
Figure 10 show the recommended decoupling scheme. All  
0.1µF capacitors must be located as close to the pins as  
possible. In addition, pins REFT, VREF, and REFB must be  
decoupled with tantalum surface-mount capacitors (2.2µF,  
4.7µF, 10µF or higher).  
RSEL  
VREF  
R2  
R1  
3.3V  
0.1µF  
15µF  
ADS5221  
402Ω  
2Ω  
REFT  
INTERNAL REFERENCE  
10µF  
2.2µF  
2.2µF  
15µF  
15µF  
There are two internal fixed reference modes and one  
internal programmable reference mode as shown in Table I  
and Figure 7 through Figure 9. Setting RSEL to ground (or  
< 0.2V) provides an internal reference voltage of +1.0V at  
VREF pin, +2V at REFT, and +1V at REFB pin. In this case,  
the input FSR is +2V peak-to-peak. Connecting RSEL to the  
VREF pin provides an internal reference voltage of +0.5V at  
2Ω  
REFB  
402Ω  
FIGURE9. InternalReferenceModeforVREF =0.5(1+R2/R1).  
VREF, +1.75V at REFT, and +1.25V at REFB. In this case, the  
input FSR is +1V peak-to-peak. Setting the resister divider as  
in Figure 9 provides an internal voltage between +0.5V and  
+1V at VREF, which is as follows:  
EXTERNAL REFERENCE  
For even more design flexibility, the ADS5221 can be oper-  
ated with external references. Utilization of an external refer-  
ence voltage may be considered for applications requiring  
higher accuracy, improved temperature stability, or flexible  
full-scale range. Particularly in multi-channel applications,  
the use of a common external reference offers the benefit of  
improving gain matching between converters. Setting RSEL  
to AVDD (+3.3V) provides an external reference mode for the  
ADS5221. In this case, the internal VREF amplifier is powered  
down, and the VREF pin requires an external reference  
voltage between +0.5V to +1V to provide an input FSR  
voltage of +1V to +2V. The REFT and REFB will appear with  
the voltage as shown in Table I and input FSR is always  
twice the voltage at the VREF pin. A voltage reference  
(REF1004 or TPS79225) and a single-supply amplifier  
(OPA2234 or OPA4227) can be used to generate a precision  
external reference.  
VREF = 0.5 (1+R2/R1)  
In this case, the voltage at REFT and REFB and input FSR  
is calculated based on Table I.  
RSEL  
VREF  
1V  
Output  
3.3V  
0.1µF  
2.2µF  
402Ω  
ADS5221  
2Ω  
REFT  
10µF  
2.2µF  
15µF  
15µF  
2Ω  
REFB  
2.2µF  
402Ω  
AVDD  
FIGURE 7. Internal Reference Mode for VREF = 1V.  
RSEL  
RSEL  
Input  
0.5V to 1V  
VREF  
VREF  
0.5V  
3.3V  
0.1µF  
10µF  
Output  
3.3V  
0.1µF  
15µF  
ADS5221  
REFT  
402Ω  
402Ω  
2Ω  
ADS5221  
2Ω  
REFT  
10µF  
2.2µF  
2.2µF  
15µF  
15µF  
10µF  
2.2µF  
15µF  
15µF  
2Ω  
2Ω  
REFB  
REFB  
402Ω  
2.2µF  
402Ω  
FIGURE 10. External Reference Configuration.  
FIGURE 8. Internal Reference Mode for VREF = 0.5V.  
ADS5221  
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the input voltage is (+FS 1 LSB) or above this value, the  
ADS5221 outputs all 1s at 12 data bits; when the input  
voltage is FS or below this value, the ADS5221 outputs all  
0s at 12 data bits. When the input voltage is 0 (middle scale)  
or only the common-mode voltage at the input, the ADS5221  
outputs 1 at MSB and 0s at the remaining 11 data bits.  
Another over-range control function of the ADS5221 is over-  
range indication, which is output by the OVR pin. The OVR  
pin is the function of the reference voltage and the output  
data bits, and has the same pipeline delay as the output data  
bits. OVR is at logic low if the input voltage is within the FSR,  
and is at logic high if the input voltage is over full-scale or  
under full-scale. OVR changes from logic low to high or logic  
high to low immediately following the change of the output  
data, when the input voltage changes from normal value to  
over FS or from over FS to normal value. When the input  
signal continues under full-scale or over full-scale, OVR  
stays high.  
DIGITAL OUTPUTS  
DATA OUTPUT FORMAT  
The ADS5221 makes two data output formats available,  
either the Straight Offset Binary (SOB) code or the Binary  
Twos Complement (BTC) code. The selection of the output  
coding is controlled through the MSBI pin. Applying a logic  
high will enable the BTC coding, whereas a logic low will  
enable the SOB code. The two code structures are identical  
with one exception: the MSB is inverted for the BTC format,  
as shown in Table II. If the input signal exceeds the FSR, the  
output code will remain at all 1s or all 0s.  
BINARY TWOS  
COMPLEMENT  
(BTC)  
STRAIGHT OFFSET  
BINARY (SOB)  
DIFFERENTIAL INPUT  
+FS 1LSB  
(+FS: VIP = 2V, VIN = 1V)  
1111 1111 1111  
1100 0000 0000  
1000 0000 0000  
0100 0000 0000  
0000 0000 0000  
0111 1111 1111  
0100 0000 0000  
0000 0000 0000  
1100 0000 0000  
1000 0000 0000  
+1/2 FS  
(VIP = 1.75V, VIN = 1.25V)  
TIMING  
Bipolar Zero  
(VIP = VIN = 1.5V)  
The ADS5221 samples the analog signal at the rising edge  
of its input clock, and outputs the digital data at the rising  
edge of the input clock after a pipeline delay of 5 clocks.  
There is an aperture delay (typically 3ns) between the  
sampling edge and the actual sampling time. There is also a  
propagation delay between the rising edge of the clock and  
the time that data is valid on the data bus (see the timing  
diagram on page 5). The output data of the ADS5221 is  
latched data.  
1/2 FS  
(VIN = 1.75V, VIP = 1.25V)  
FS  
(VIN = 2V, VIP = 1V)  
TABLE II. Coding Table for Differential Input Configuration  
with FSR of 2V.  
OUTPUT ENABLE (OE  
)
The digital outputs of the ADS5221 can be set to output  
enable or output high impedance (tri-state) by the OE pin.  
For normal operation, this pin must be at a logic low, whereas  
a logic high disables the outputs or sets the output tri-state.  
POWER SUPPLIES AND  
POWER DISSIPATION  
ANALOG AND DIGITAL POWER SUPPLY  
OUTPUT LOADING  
The ADS5221 includes power-supply pins of AVDD, DVDD  
and VDRV. The analog supply AVDD is +3.3V and digital  
supply DVDD is +3.3V. A digital output driver supply, VDRV,  
can be +2.5V up to +3.3V. AVDD, DVDD and VDRV are not  
tied together internally. Each of these supply pins must be  
bypassed separately with at least one 0.1µF ceramic chip  
capacitor. The analog supply (AVDD) and the digital supply  
(DVDD or VDRV) may be tied together externally with a ferrite  
bead or inductor between the supply pins. The digital output  
driver supply, VDRV, of +2.5V is used commonly. It is highly  
recommended to consider linear supplies instead of switch-  
ing types. Even with good filtering, switching supplies can  
radiate noise that could interfere with any high-frequency  
input signal and cause unwanted modulation products. The  
supply voltage should stay within the tolerance given in the  
specification table. A basic application configuration with the  
power supply decoupling is shown in Figure 11.  
It is recommended to keep the capacitive loading on the data  
output lines as low as possible, preferably below 5pF. Higher  
capacitive loading will cause larger dynamic currents as the  
digital outputs are changing. These high current surges can  
feed back to the analog portion of the ADC and adversely  
affect device performance. If necessary, external buffers or  
latches (for example, the SN74LVTH16374) close to the  
converter output pins can be used to minimize capacitive  
loading. Buffers or latches also provide the added benefit of  
isolating the ADS5221 from any digital activities on the bus  
to limit the high-frequency noise.  
OVER-RANGE INDICATOR  
The ADS5221 has control functions for the input voltage over  
full-scale that includes output data code control and over-  
range indication. The output data code control of over full-  
scale is shown in Table II. In SOB format, for example, when  
ADS5221  
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DVDD  
AVDD  
10µF  
+
10µF  
+
0.10µF  
0.10µF  
2.2µF  
+
0.10µF  
30  
31  
42  
26  
25  
24  
23  
22  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
VREF  
RSEL  
IN  
NC  
NC  
24.9Ω  
24.9Ω  
1.5V  
1.5V  
OVR  
22pF  
NC  
41  
35  
LATCH  
IN  
NC  
NC  
D11 (MSB)  
D10  
D9  
15µF  
2.2µF  
402Ω  
402Ω  
2Ω  
2Ω  
+
34  
REFT  
+3.3  
33  
32  
10µF  
NC  
D8  
REFB  
D7  
+
ADS5221  
15µF  
2.2µF  
38  
39  
40  
43  
44  
D6  
AGND  
AGND  
AGND  
AGND  
DGND  
DGND  
D5  
D4  
D3  
D2  
45  
27  
28  
29  
D1  
21  
D0 (LSB)  
AGND  
AGND  
AGND  
SN74LVTH16374  
46  
CLK  
+
VPULSE  
49.9Ω  
0.10µF  
10µF  
+
VDRV  
NC = No Connection.  
FIGURE 11. General Layout for the ADS5221.  
POWER DOWN (PD)  
POWER DISSIPATION  
The ADS5221 provides two power-down modes for different  
application requirements. One is standard power down  
(STPD); the second is quasi power down (QPD). Setting  
STPD to logic high (and QPD to logic low or high) will shut  
down the internal ADC core and power down the reference  
circuit. In this case the power dissipation is typically 15mW.  
With 10µF external decoupling capacitor at REFT and REFB,  
it takes about 800µs to fully restore normal operation after the  
normal mode is enabled. Setting QPD to logic high (and  
STPD to logic low) will shut down the internal ADC core and  
while the internal reference circuit power remains on. In this  
In normal operating mode (STPD = low and QPD = low), the  
typical total power dissipation of the ADS5221 is 285mW.  
The majority of the power consumption is due to biasing;  
therefore, this part of the total power dissipation is indepen-  
dent of the applied clock frequency. The digital power dissi-  
pation from the output driver is less than 10% of the total  
power dissipation. This portion of the power consumption is  
proportional to the sampling rate, digital output load and  
number of the bits. The current on the VDRV supply is  
directly related to the capacitive loading of the data output  
pins; care must be taken to minimize such loading.  
ADS5221  
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case, power dissipation is typically 70mW. It takes about 2µs  
to fully restore normal operation after the normal mode is  
enabled. During power-down, data in the converter pipeline  
will be lost and new valid data will be subject to the specified  
pipeline delay.  
supply pins DVDD and driver supply pins, VDRV. In order to  
minimize the lead and trace inductance, the capacitors must  
be located as close to the supply pins as possible. They are  
best placed directly under the package where double-sided  
component mounting is allowed. In addition, larger bipolar  
decoupling capacitors (2.2µF to 10µF), effective at lower  
frequencies, must also be used on the main supply pins.  
They can be placed on the PC board in close proximity  
(< 0.5 inches) to the ADC. If the analog inputs to the  
ADS5221 are driven differentially, it is especially important to  
optimize towards a highly symmetrical layout. Small trace  
length differences can create phase shifts compromising a  
good distortion performance. For this reason, the use of two  
single op amps rather than one dual amplifier enables a more  
symmetrical layout and a better match of parasitic capaci-  
tances. The pin orientation of the ADS5221 package follows  
a flow-through design with the analog inputs located on one  
side of the package, whereas the digital outputs are located  
on the opposite side of the quad-flat package. This provides  
a good physical isolation between the analog and digital  
connections. While designing the layout, it is important to  
keep the analog signal traces separated from any digital lines  
to prevent noise coupling onto the analog portion. Try to  
match trace length for the differential clock signal (if used) to  
avoid mismatches in propagation delays. Single-ended clock  
lines must be short and should not cross any other signal  
traces. Short circuit traces on the digital outputs will minimize  
capacitive loading. Trace length must be kept short to the  
receiving gate (< 2 inches) with only one CMOS gate con-  
nected to one digital output. If possible, the digital data  
outputs must be buffered (with the TI SN74LTH16374, for  
example). Dynamic performance can also be improved with  
the insertion of series resistors at each data output line. This  
sets a defined time constant and reduces the slew rate that  
would otherwise flow as the fast edge rate. The resistor value  
may be chosen to give a time constant of 15% to 25% of the  
used data.  
LAYOUT AND DECOUPLING  
Proper grounding and bypassing, short lead length, and the  
use of ground planes are particularly important for high-  
frequency designs. Achieving optimum performance with a  
fast sampling converter like the ADS5221 requires careful  
attention to the PC board layout in order to minimize the  
effect of board parasitics and optimize component place-  
ment. A multi-layer board usually ensures best results and  
allows convenient component placement. The ADS5221 must  
be treated as an analog component, and the AVDD pins  
connected to a clean analog supply. This ensures the most  
consistent results, because digital supplies often carry a high  
level of switching noise that could couple into the converter  
and degrade the performance. The driver supply pins (VDRV)  
must also be connected to a low-noise supply. Supplies of  
adjacent digital circuits can carry substantial current tran-  
sients. The supply voltage must be thoroughly filtered before  
connecting to the VDRV supply of the converter. All ground  
connections on the ADS5221 are internally bonded to the  
metal flag (bottom of package) that forms a large ground  
plane. All ground pins must directly connect to an analog  
ground plane that covers the PC board area under the  
converter. Due to its high sampling frequency, the ADS5221  
generates high frequency current transients and noise (clock  
feedthrough) that are fed back into the supply and reference  
lines. If not sufficiently bypassed, this adds noise to the  
conversion process. See Figure 11 for the recommended  
supply decoupling scheme for the ADS5221. All AVDD pins  
should be bypassed with a combination of 0.1µF ceramic  
chip capacitors (0805, low ESR) and a 10µF tantalum tank  
capacitor. A similar approach may be used on the digital  
ADS5221  
16  
SBAS262A  
www.ti.com  
PACKAGE OPTION ADDENDUM  
www.ti.com  
9-Dec-2004  
PACKAGING INFORMATION  
Orderable Device  
Status (1)  
Package Package  
Pins Package Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)  
Qty  
Type  
TQFP  
TQFP  
Drawing  
ADS5221PFBR  
ADS5221PFBT  
ACTIVE  
ACTIVE  
PFB  
48  
48  
2500  
250  
None  
None  
CU NIPDAU Level-2-220C-1 YEAR  
CU NIPDAU Level-2-220C-1 YEAR  
PFB  
(1) The marketing status values are defined as follows:  
ACTIVE: Product device recommended for new designs.  
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.  
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in  
a new design.  
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.  
OBSOLETE: TI has discontinued the production of the device.  
(2)  
Eco Plan - May not be currently available - please check http://www.ti.com/productcontent for the latest availability information and additional  
product content details.  
None: Not yet available Lead (Pb-Free).  
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements  
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered  
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.  
Green (RoHS & no Sb/Br): TI defines "Green" to mean "Pb-Free" and in addition, uses package materials that do not contain halogens,  
including bromine (Br) or antimony (Sb) above 0.1% of total product weight.  
(3)  
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDECindustry standard classifications, and peak solder  
temperature.  
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is  
provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the  
accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take  
reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on  
incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited  
information may not be available for release.  
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI  
to Customer on an annual basis.  
Addendum-Page 1  
MECHANICAL DATA  
MTQF019A – JANUARY 1995 – REVISED JANUARY 1998  
PFB (S-PQFP-G48)  
PLASTIC QUAD FLATPACK  
0,27  
0,17  
0,50  
M
0,08  
36  
25  
37  
24  
48  
13  
0,13 NOM  
1
12  
5,50 TYP  
7,20  
SQ  
Gage Plane  
6,80  
9,20  
SQ  
8,80  
0,25  
0,05 MIN  
0°7°  
1,05  
0,95  
0,75  
0,45  
Seating Plane  
0,08  
1,20 MAX  
4073176/B 10/96  
NOTES: A. All linear dimensions are in millimeters.  
B. This drawing is subject to change without notice.  
C. Falls within JEDEC MS-026  
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