MAX1279BCTC [MAXIM]

ADC, Successive Approximation, 12-Bit, 1 Func, 1 Channel, Serial Access, BICMOS, 4 X 4 MM, 0.80 MM HEIGHT, MO-220-WGGB, TQFN-12;
MAX1279BCTC
型号: MAX1279BCTC
厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述:

ADC, Successive Approximation, 12-Bit, 1 Func, 1 Channel, Serial Access, BICMOS, 4 X 4 MM, 0.80 MM HEIGHT, MO-220-WGGB, TQFN-12

文件: 总18页 (文件大小:346K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
19-3365; Rev 1; 4/09  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
General Description  
Features  
The MAX1277/MAX1279 are low-power, high-speed, seri-  
al-output, 12-bit, analog-to-digital converters (ADCs) with  
an internal reference that operates at up to 1.5Msps.  
These devices feature true-differential inputs, offering bet-  
ter noise immunity, distortion improvements, and a wider  
dynamic range over single-ended inputs. A standard  
SPI™/QSPI™/MICROWIRE™ interface provides the clock  
necessary for conversion. These devices easily interface  
with standard digital signal processor (DSP) synchronous  
serial interfaces.  
o 1.5Msps Sampling Rate  
o Only 22mW (typ) Power Dissipation  
o Only 1µA (max) Shutdown Current  
o High-Speed, SPI-Compatible, 3-Wire Serial Interface  
o 68.5dB S/(N + D) at 525kHz Input Frequency  
o Internal True-Differential Track/Hold (T/H)  
o Internal 2.048V Reference  
o No Pipeline Delays  
The MAX1277/MAX1279 operate from a single +2.7V to  
+3.6V supply voltage. The MAX1277/MAX1279 include a  
2.048V internal reference. The MAX1277 has a unipolar  
analog input, while the MAX1279 has a bipolar analog  
input. These devices feature a partial power-down mode  
and a full power-down mode for use between conver-  
sions, which lower the supply current to 2mA (typ) and  
1µA (max), respectively. Also featured is a separate  
o Small 12-Pin TQFN Package  
power-supply input (V ), which allows direct interfacing to  
L
+1.8V to V  
digital logic. The fast conversion speed,  
DD  
low-power dissipation, excellent AC performance, and DC  
accuracy ( 1 LSꢀ IꢁL) make the MAX1277/MAX1279  
ideal for industrial process control, motor control, and  
base-station applications.  
Ordering Information  
PIN-  
PACKAGE  
PART  
TEMP RANGE  
INPUT  
The MAX1277/MAX1279 come in a 12-pin TQFꢁ pack-  
age, and are available in the extended (-40°C to +85°C)  
temperature range.  
MAX1277AETC-T -40°C to +85°C 12 TQFꢁ  
MAX1277ꢀETC-T -40°C to +85°C 12 TQFꢁ  
MAX1279AETC-T -40°C to +85°C 12 TQFꢁ  
MAX1279ꢀETC-T -40°C to +85°C 12 TQFꢁ  
Unipolar  
Unipolar  
ꢀipolar  
ꢀipolar  
Applications  
Data Acquisition  
ꢀill Validation  
Motor Control  
Communications  
Portable Instruments  
Typical Operating Circuit  
Pin Configuration  
+1.8V TO V  
DD  
+2.7V TO +3.6V  
TOP VIEW  
AIN+  
12  
N.C.  
SCLK  
10  
0.01μF  
0.01μF  
10μF  
10μF  
11  
V
V
L
DD  
AIN-  
REF  
1
2
3
9
8
7
CNVST  
DOUT  
DIFFERENTIAL  
INPUT  
+
-
DOUT  
AIN+  
AIN-  
VOLTAGE  
MAX1277  
MAX1279  
μC/DSP  
MAX1277  
MAX1279  
RGND  
V
L
CNVST  
SCLK  
REF  
4
5
6
RGND  
GND  
V
N.C.  
GND  
4.7μF  
0.01μF  
DD  
TQFN  
SPI/QSPI are trademarks of Motorola, Inc.  
MICROWIRE is a trademark of ꢁational Semiconductor Corp.  
________________________________________________________________ Maxim Integrated Products  
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,  
or visit Maxim’s website at www.maxim-ic.com.  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
ABSOLUTE MAXIMUM RATINGS  
DD  
V
to GꢁD..............................................................-0.3V to +6V  
Maximum Current into Any Pin............................................50mA  
V to GꢁD ................-0.3V to the lower of (V  
Digital Inputs  
to GꢁD .................-0.3V to the lower of (V  
Digital Output  
to GꢁD....................-0.3V to the lower of (V + 0.3V) and +6V  
Analog Inputs and  
REF to GꢁD..........-0.3V to the lower of (V  
+ 0.3V) and +6V  
Continuous Power Dissipation (T = +70°C)  
12-Pin TQFꢁ (derate 16.9mW/°C above +70°C) ......1349mW  
Operating Temperature Range  
MAX127_ _ ETC..............................................-40°C to +85°C  
Junction Temperature......................................................+150°C  
Storage Temperature Range.............................-60°C to +150°C  
Lead Temperature (soldering, 10s) .................................+300°C  
L
DD  
A
+ 0.3V) and +6V  
DD  
L
+ 0.3V) and +6V  
DD  
RGꢁD to GꢁD .......................................................-0.3V to +0.3V  
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional  
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to  
absolute maximum rating conditions for extended periods may affect device reliability.  
ELECTRICAL CHARACTERISTICS  
(V  
= +2.7V to +3.6V, V = V , f  
= 24MHz, 50% duty cycle, T = -40°C to +85°C, unless otherwise noted. Typical values are  
DD  
L
DD SCLK A  
at T = +25°C.)  
A
/MAX1279  
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
DC ACCURACY  
Resolution  
12  
ꢀits  
LSꢀ  
MAX127_A  
MAX127_ꢀ  
MAX127_A  
MAX127_ꢀ  
-1.0  
-1.5  
-1.0  
-1.0  
+1.0  
+1.5  
+1.0  
+1.5  
8.0  
Relative Accuracy (ꢁote 1)  
IꢁL  
Differential ꢁonlinearity (ꢁote 2)  
Offset Error  
DꢁL  
LSꢀ  
LSꢀ  
Offset-Error Temperature  
Coefficient  
1
2
ppm/°C  
Gain Error  
Offset nulled  
6.0  
LSꢀ  
Gain Temperature Coefficient  
ppm/°C  
DYNAMIC SPECIFICATIONS (f = 525kHz sine wave, V = V , unless otherwise noted.)  
REF  
IN  
IN  
SIꢁAD  
THD  
66  
68.5  
-80  
-83  
-78  
15  
dꢀ  
dꢀ  
Signal-to-ꢁoise Plus Distortion  
Total Harmonic Distortion  
Spurious-Free Dynamic Range  
Intermodulation Distortion  
Full-Power ꢀandwidth  
Up to the 5th harmonic  
= 250kHz, f = 300kHz  
-76  
-76  
SFDR  
IMD  
dꢀ  
f
dꢀ  
Iꢁ1  
Iꢁ2  
-3dꢀ point, small-signal method  
S/(ꢁ + D) > 68dꢀ, single ended  
MHz  
MHz  
Full-Linear ꢀandwidth  
1.2  
CONVERSION RATE  
Minimum Conversion Time  
Maximum Throughput Rate  
Minimum Throughput Rate  
t
(ꢁote 3)  
0.667  
µs  
Msps  
ksps  
ns  
COꢁV  
1.5  
10  
(ꢁote 4)  
(ꢁote 5)  
Track-and-Hold Acquisition Time  
Aperture Delay  
t
125  
5
ACQ  
ns  
Aperture Jitter  
(ꢁote 6)  
(ꢁote 7)  
30  
ps  
External Clock Frequency  
f
24  
MHz  
SCLK  
2
_______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
ELECTRICAL CHARACTERISTICS (continued)  
(V  
= +2.7V to +3.6V, V = V , f  
= 24MHz, 50% duty cycle, T = -40°C to +85°C, unless otherwise noted. Typical values are  
DD  
L
DD SCLK A  
at T = +25°C.)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
ANALOG INPUTS (AIN+, AIN-)  
AIꢁ+ - AIꢁ-, MAX1277  
0
V
REF  
Differential Input Voltage Range  
V
V
Iꢁ  
AIꢁ+ - AIꢁ-, MAX1279  
-V  
/ 2  
+V  
/ 2  
REF  
REF  
Absolute Input Voltage Range  
DC Leakage Current  
0
V
V
DD  
1
µA  
pF  
µA  
Input Capacitance  
Per input pin  
16  
75  
Input Current (Average)  
REFERENCE OUTPUT (REF)  
REF Output Voltage Range  
Voltage Temperature Coefficient  
Time averaged at maximum throughput rate  
Static, T = +25°C  
2.038  
2.048  
50  
2.058  
V
A
ppm/°C  
I
I
= 0 to 2mA  
0.35  
1.0  
SOURCE  
Load Regulation  
mV/mA  
mV/V  
= 0 to 100µA  
SIꢁK  
Line Regulation  
V
= 2.7V to 3.6V, static  
0.25  
DD  
DIGITAL INPUTS (SCLK, CNVST)  
Input Voltage Low  
VIL  
0.3 x V  
10  
V
V
L
Input Voltage High  
VIH  
0.7 x V  
L
Input Leakage Current  
DIGITAL OUTPUT (DOUT)  
Output Load Capacitance  
Output Voltage Low  
I
0.05  
0.2  
µA  
IL  
C
For stated timing performance  
30  
pF  
V
OUT  
V
I
I
= 5mA, V 1.8V  
0.4  
OL  
OH  
OL  
SIꢁK  
L
Output Voltage High  
V
= 1mA, V 1.8V  
V - 0.5V  
L
V
SOURCE  
L
Output Leakage Current  
POWER REQUIREMENTS  
Analog Supply Voltage  
Digital Supply Voltage  
I
Output high impedance  
10  
µA  
V
2.7  
1.8  
3.6  
V
V
DD  
V
V
L
DD  
8
Static, f  
= 24MHz  
6
5
SCLK  
Analog Supply Current,  
ꢁormal Mode  
I
Static, no SCLK  
7
mA  
DD  
Operational, 1.5Msps  
7
9
f
= 24MHz  
2
SCLK  
Analog Supply Current,  
Partial Power-Down Mode  
I
I
mA  
µA  
DD  
ꢁo SCLK  
= 24MHz  
2
f
1
SCLK  
Analog Supply Current,  
Full Power-Down Mode  
DD  
ꢁo SCLK  
0.3  
0.3  
0.15  
1
1
Operational, full-scale input at 1.5Msps  
Static, f  
= 24MHz  
0.5  
SCLK  
mA  
Digital Supply Current (ꢁote 8)  
Positive-Supply Rejection  
Partial/full power-down mode,  
= 24MHz  
0.1  
0.3  
f
SCLK  
Static, no SCLK, all modes  
= 3V +20% -10%, full-scale input  
0.1  
0.2  
1
µA  
PSR  
V
3.0  
mV  
DD  
_______________________________________________________________________________________  
3
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
TIMING CHARACTERISTICS  
(V  
= +2.7V to +3.6V, V = V , f  
= 24MHz, 50% duty cycle, T = -40°C to +85°C, unless otherwise noted. Typical values are  
DD  
L
DD SCLK A  
at T = +25°C.)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
MAX  
UNITS  
V = 2.7V to V  
18.7  
L
DD  
SCLK Pulse-Width High  
SCLK Pulse-Width Low  
t
ns  
CH  
V = 1.8V to V , minimum recommended  
(ꢁote 7)  
L
DD  
22.5  
V = 2.7V to V  
18.7  
L
DD  
t
ns  
ns  
CL  
V = 1.8V to V , minimum recommended  
L
DD  
22.5  
(ꢁote 7)  
C = 30pF, V = 2.7V to V  
17  
24  
L
L
DD  
SCLK Rise to DOUT Transition  
t
DOUT  
C = 30pF, V = 1.8V to V  
L
L
DD  
DOUT Remains Valid After SCLK  
CꢁVST Fall to SCLK Fall  
t
V = 1.8V to V  
4
ns  
ns  
DHOLD  
L
DD  
DD  
DD  
t
V = 1.8V to V  
L
10  
20  
SETUP  
CꢁVST Pulse Width  
t
V = 1.8V to V  
L
ns  
CSW  
/MAX1279  
Power-Up Time; Full Power-Down  
Restart Time; Partial Power-Down  
t
2
ms  
PWR-UP  
t
16  
Cycles  
RCV  
Note 1: Relative accuracy is the deviation of the analog value at any code from its theoretical value after the gain error and the offset  
error have been nulled.  
Note 2: ꢁo missing codes over temperature.  
Note 3: Conversion time is defined as the number of clock cycles (16) multiplied by the clock period.  
Note 4: At sample rates below 10ksps, the input full-linear bandwidth is reduced to 5kHz.  
Note 5: The listed value of three SCLK cycles is given for full-speed continuous conversions. Acquisition time begins on the 14th ris-  
ing edge of SCLK and terminates on the next falling edge of CꢁVST. The IC idles in acquisition mode between conversions.  
Note 6: Undersampling at the maximum signal bandwidth requires the minimum jitter spec for SIꢁAD performance.  
Note 7: 1.5Msps operation guaranteed for V > 2.7V. See the Typical Operating Characteristics section for recommended sampling  
L
speeds for V < 2.7V.  
L
Note 8: Digital supply current is measured with the V level equal to V , and the V level equal to GꢁD.  
IH  
L
IL  
V
L
CNVST  
SCLK  
t
CSW  
6kΩ  
t
CL  
t
SETUP  
t
CH  
DOUT  
DOUT  
6kΩ  
C
L
C
L
t
DHOLD  
t
DOUT  
DOUT  
GND  
b) HIGH-Z TO V , V TO V ,  
OL  
GND  
a) HIGH-Z TO V , V TO V  
,
OH OL  
OH  
OL OH  
AND V TO HIGH-Z  
OH  
AND V TO HIGH-Z  
OL  
Figure 1. Detailed Serial-Interface Timing  
Figure 2. Load Circuits for Enable/Disable Times  
4
_______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
Typical Operating Characteristics  
(V  
DD  
= +3V, V = V , f  
= 24MHz, f  
= 1.5Msps, T = -40°C to +85°C, unless otherwise noted. Typical values are mea-  
L
DD SCLK  
SAMPLE A  
sured at T = +25°C.)  
A
INTEGRAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE (MAX1277)  
INTEGRAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE (MAX1279)  
MAXIMUM RECOMMENDED f  
vs. V  
L
SCLK  
1.00  
25  
23  
21  
19  
17  
1.00  
0.75  
0.50  
0.25  
0
0.75  
0.50  
0.25  
0
-0.25  
-0.50  
-0.75  
-1.00  
-0.25  
-0.50  
-0.75  
-1.00  
0
1024  
2048  
3072  
4096  
1.8  
2.1  
2.4  
2.7  
3.0  
3.3  
3.6  
-2048  
-1024  
0
1024  
2048  
DIGITAL OUTPUT CODE  
V (V)  
L
DIGITAL OUTPUT CODE  
DIFFERENTIAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE (MAX1277)  
DIFFERENTIAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE (MAX1279)  
OFFSET ERROR  
vs. TEMPERATURE (MAX1277)  
1.00  
0.75  
0.50  
0.25  
0
1.00  
0.75  
0.50  
0.25  
0
0
-1  
-2  
-3  
-4  
-5  
-6  
-0.25  
-0.50  
-0.75  
-1.00  
-0.25  
-0.50  
-0.75  
-1.00  
0
1024  
2048  
3072  
4096  
-2048  
-1024  
0
1024  
2048  
-40  
-15  
10  
35  
60  
85  
DIGITAL OUTPUT CODE  
DIGITAL OUTPUT CODE  
TEMPERATURE (°C)  
GAIN ERROR  
vs. TEMPERATURE (MAX1279)  
OFFSET ERROR  
vs. TEMPERATURE (MAX1279)  
GAIN ERROR  
vs. TEMPERATURE (MAX1277)  
2
0
4
3
1
0
-1  
-2  
-3  
-4  
-5  
-6  
2
-1  
-2  
-3  
-4  
1
0
-1  
-2  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
_______________________________________________________________________________________  
5
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
Typical Operating Characteristics (continued)  
(V  
DD  
= +3V, V = V , f  
= 24MHz, f  
= 1.5Msps, T = -40°C to +85°C, unless otherwise noted. Typical values are mea-  
L
DD SCLK  
SAMPLE A  
sured at T = +25°C.)  
A
DYNAMIC PERFORMANCE  
vs. INPUT FREQUENCY (MAX1279)  
DYNAMIC PERFORMANCE  
vs. INPUT FREQUENCY (MAX1277)  
70.0  
69.5  
69.0  
68.5  
68.0  
70.0  
69.5  
69.0  
68.5  
68.0  
SNR  
SNR  
SINAD  
SINAD  
100  
200  
300  
400  
500  
500  
750  
100  
200  
300  
400  
500  
ANALOG INPUT FREQUENCY (kHz)  
/MAX1279  
ANALOG INPUT FREQUENCY (kHz)  
THD vs. INPUT FREQUENCY  
SFDR vs. INPUT FREQUENCY  
-80  
-84  
-88  
-92  
-96  
92  
90  
88  
86  
84  
82  
MAX1277  
MAX1279  
MAX1277  
MAX1279  
100  
200  
300  
400  
500  
100  
200  
300  
400  
ANALOG INPUT FREQUENCY (kHz)  
ANALOG INPUT FREQUENCY (kHz)  
FFT PLOT (MAX1277)  
FFT PLOT (MAX1279)  
0
-20  
0
-20  
f
= 500kHz  
f = 500kHz  
IN  
IN  
SINAD = 68.7dB  
SNR = 68.9dB  
THD = -83.1dB  
SFDR = 85.0dB  
SINAD = 69.0dB  
SNR = 69.1dB  
THD = -88.9dB  
SFDR = 85.9dB  
-40  
-40  
-60  
-60  
-80  
-80  
-100  
-120  
-140  
-100  
-120  
-140  
0
125  
250  
375  
500  
625  
750  
0
125  
250  
375  
500  
625  
ANALOG INPUT FREQUENCY (kHz)  
ANALOG INPUT FREQUENCY (kHz)  
6
_______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
Typical Operating Characteristics (continued)  
(V  
DD  
= +3V, V = V , f  
= 24MHz, f  
= 1.5Msps, T = -40°C to +85°C, unless otherwise noted. Typical values are mea-  
L
DD SCLK  
SAMPLE A  
sured at T = +25°C.)  
A
TOTAL HARMONIC DISTORTION  
vs. SOURCE IMPEDANCE  
TWO-TONE IMD PLOT (MAX1277)  
-50  
-60  
0
-20  
f
f
= 250.102kHz  
= 299.966kHz  
IN1  
IN2  
IMD = -88.4dB  
f
= 500kHz  
-40  
IN  
f
IN1  
f
IN2  
-70  
-60  
-80  
-80  
-100  
-120  
-140  
f
= 100kHz  
IN  
-90  
-100  
10  
100  
1000  
0
125  
250  
375  
500  
625  
750  
SOURCE IMPEDANCE (Ω)  
ANALOG INPUT FREQUENCY (kHz)  
V
DD  
/V FULL POWER-DOWN  
L
SUPPLY CURRENT vs. TEMPERATURE  
TWO-TONE IMD PLOT (MAX1279)  
1.00  
0.80  
0.60  
0.40  
0.20  
0
0
-20  
f
f
= 250.102kHz  
= 299.966kHz  
IN1  
IN2  
IMD = -85.2dB  
-40  
f
IN1  
f
IN2  
-60  
V , NO SCLK  
, NO SCLK  
L
V
DD  
-80  
V
, SCLK = 24MHz  
DD  
-100  
-120  
-140  
-40  
-15  
10  
35  
60  
85  
0
125  
250  
375  
500  
625  
750  
TEMPERATURE (°C)  
ANALOG INPUT FREQUENCY (kHz)  
V
DD  
SUPPLY CURRENT  
vs. TEMPERATURE  
V PARTIAL/FULL POWER-DOWN  
L
SUPPLY CURRENT vs. TEMPERATURE  
9.0  
7.5  
6.0  
4.5  
3.0  
1.5  
0
100  
75  
CONVERSION  
V , = 1.8V, SCLK = 24MHz  
L
V , = 3V, SCLK = 24MHz  
L
50  
PARTIAL POWER-DOWN  
25  
0
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
_______________________________________________________________________________________  
7
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
Typical Operating Characteristics (continued)  
(V  
DD  
= +3V, V = V , f  
= 24MHz, f  
= 1.5Msps, T = -40°C to +85°C, unless otherwise noted. Typical values are mea-  
L
DD SCLK  
SAMPLE A  
sured at T = +25°C.)  
A
V
DD  
SUPPLY CURRENT  
V SUPPLY CURRENT  
L
vs. CONVERSION RATE  
vs. TEMPERATURE  
8
6
4
2
0
0.50  
0.40  
0.30  
0.20  
0.10  
0
CONVERSION, V = 3V  
L
CONVERSION, V = 1.8V  
L
0
250  
500  
750 1000 1250 1500  
(kHz)  
-40  
-15  
10  
35  
60  
85  
/MAX1279  
f
TEMPERATURE (°C)  
SAMPLE  
V SUPPLY CURRENT  
L
vs. CONVERSION RATE  
REFERENCE VOLTAGE  
vs. TEMPERATURE  
250  
200  
150  
100  
50  
2.06  
2.05  
2.04  
2.03  
2.02  
2.01  
2.00  
V = 3V  
L
V = 1.8V  
L
0
0
250  
500  
f
750 1000 1250 1500  
(kHz)  
-40  
-15  
10  
35  
60  
85  
TEMPERATURE (°C)  
SAMPLE  
REFERENCE VOLTAGE  
vs. LOAD CURRENT (SOURCE)  
REFERENCE VOLTAGE  
vs. LOAD CURRENT (SINK)  
2.05  
2.04  
2.03  
2.02  
2.01  
2.08  
2.07  
2.06  
2.05  
2.04  
0
2
4
6
8
0
50  
100  
150  
200  
LOAD CURRENT (mA)  
LOAD CURRENT (μA)  
8
_______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
Pin Description  
PIN  
NAME  
FUNCTION  
1
AIꢁ-  
ꢁegative Analog Input  
Reference Voltage Output. Internal 2.048V reference output. ꢀypass REF with a 0.01µF capacitor and  
a 4.7µF capacitor to RGꢁD.  
2
3
4
REF  
RGꢁD  
Reference Ground. Connect RGꢁD to GꢁD.  
Positive Analog Supply Voltage (+2.7V to +3.6V). ꢀypass V  
capacitor to GꢁD.  
with a 0.01µF capacitor and a 10µF  
DD  
V
DD  
5, 11  
6
ꢁ.C.  
ꢁo Connection  
GꢁD  
Ground. GꢁD is internally connected to EP.  
Positive Logic Supply Voltage (1.8V to V ). ꢀypass V with a 0.01µF capacitor and a 10µF capacitor  
to GꢁD.  
DD  
L
7
8
9
V
L
DOUT  
Serial Data Output. Data is clocked out on the rising edge of SCLK.  
Convert Start. Forcing CꢁVST high prepares the part for a conversion. Conversion begins on the  
falling edge of CꢁVST. The sampling instant is defined by the falling edge of CꢁVST.  
CꢁVST  
10  
12  
SCLK  
AIꢁ+  
EP  
Serial Clock Input. Clocks data out of the serial interface. SCLK also sets the conversion speed.  
Positive Analog Input  
Exposed Paddle. EP is internally connected to GꢁD.  
V
L
CAPACITIVE  
DAC  
V
DD  
C
IN+  
R
IN+  
REF  
REF  
AIN+  
AIN-  
2.048V  
AIN +  
12-BIT  
SAR  
ADC  
CONTROL  
LOGIC  
OUTPUT  
BUFFER  
TRACK AND  
HOLD  
COMP  
V
AZ  
DOUT  
AIN -  
R
IN-  
C
IN-  
ACQUISITION MODE  
CNVST  
SCLK  
CONTROL  
LOGIC AND  
TIMING  
CAPACITIVE  
DAC  
RGND  
MAX1277  
MAX1279  
C
IN+  
R
IN+  
AIN+  
AIN-  
GND  
CONTROL  
LOGIC  
COMP  
V
AZ  
Figure 3. Functional Diagram  
Detailed Description  
R
IN-  
C
IN-  
The MAX1277/MAX1279 use an input T/H and succes-  
sive-approximation register (SAR) circuitry to convert  
an analog input signal to a digital 12-bit output. The  
serial interface requires only three digital lines (SCLK,  
CꢁVST, and DOUT) and provides easy interfacing to  
microprocessors (µPs) and DSPs. Figure 3 shows the  
simplified internal structure for the MAX1277/MAX1279.  
HOLD/CONVERSION MODE  
Figure 4. Equivalent Input Circuit  
_______________________________________________________________________________________  
9
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
signal bandwidth, making it possible to digitize high-  
speed transient events and measure periodic  
signals with bandwidths exceeding the ADC’s sampling  
rate by using undersampling techniques. To avoid  
high-frequency signals being aliased into the frequency  
band of interest, anti-alias filtering is recommended.  
True-Differential Analog Input T/H  
The equivalent circuit of Figure 4 shows the input archi-  
tecture of the MAX1277/MAX1279, which is composed  
of a T/H, a comparator, and a switched-capacitor digi-  
tal-to-analog converter (DAC). The T/H enters its track-  
ing mode on the 14th SCLK rising edge of the previous  
conversion. Upon power-up, the T/H enters its tracking  
mode immediately. The positive input capacitor is con-  
nected to AIꢁ+. The negative input capacitor is con-  
nected to AIꢁ-. The T/H enters its hold mode on the  
falling edge of CꢁVST and the difference between the  
sampled positive and negative input voltages is convert-  
ed. The time required for the T/H to acquire an input sig-  
nal is determined by how quickly its input capacitance is  
charged. If the input signal’s source impedance is high,  
the acquisition time lengthens. The acquisition time,  
Analog Input Protection  
Internal protection diodes that clamp the analog input  
to V  
and GꢁD allow the analog input pins to swing  
DD  
from GꢁD - 0.3V to V  
+ 0.3V without damage. ꢀoth  
DD  
inputs must not exceed V  
accurate conversions.  
or be lower than GꢁD for  
DD  
Serial Interface  
Initialization After Power-Up  
and Starting a Conversion  
t
, is the minimum time needed for the signal to be  
ACQ  
Upon initial power-up, the MAX1277/MAX1279 require a  
complete conversion cycle to initialize the internal cali-  
bration. Following this initial conversion, the part is ready  
for normal operation. This initialization is only required  
after a hardware power-up sequence and is not required  
after exiting partial or full power-down mode.  
acquired. It is calculated by the following equation:  
/MAX1279  
t
9 × (RS + R ) × 16pF  
ACQ  
Iꢁ  
where R = 200Ω, and RS is the source impedance of  
Iꢁ  
the input signal.  
Note: t  
is never less than 125ns and any source  
ACQ  
impedance below 12Ω does not significantly affect the  
To start a conversion, pull CꢁVST low. At CꢁVST’s  
falling edge, the T/H enters its hold mode and a conver-  
sion is initiated. SCLK runs the conversion and the data  
can then be shifted out serially on DOUT.  
ADC’s AC performance.  
Input Bandwidth  
The ADC’s input-tracking circuitry has a 15MHz small-  
CNVST  
t
SETUP  
t
POWER-MODE SELECTION WINDOW  
8
ACQUIRE  
CONTINUOUS-CONVERSION  
SELECTION WINDOW  
1
2
3
4
14  
16  
SCLK  
HIGH IMPEDANCE  
DOUT  
D11 D10  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
Figure 5. Interface-Timing Sequence  
CONVST MUST GO HIGH AFTER THE 3RD BUT BEFORE THE 14TH SCLK RISING EDGE  
DOUT GOES HIGH IMPEDANCE ONCE CNVST GOES HIGH  
CNVST  
ONE 8-BIT TRANSFER  
SCLK  
1ST SCLK RISING EDGE  
DOUT  
0
0
0
D11  
D10  
D9  
D8  
D7  
MODE  
REF  
NORMAL  
PPD  
ENABLED (2.048V)  
Figure 6. SPI Interface—Partial Power-Down Mode  
10 ______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
Full power-down mode is ideal for infrequent data sam-  
pling and very low supply current applications. The  
MAX1277/MAX1279 have to be in partial power-down  
mode to enter full power-down mode. Perform the  
SCLK/CꢁVST sequence described above to enter par-  
tial power-down mode. Then repeat the same  
sequence to enter full power-down mode (see Figure  
7). Drive CꢁVST low, and allow at least 14 SCLK cycles  
to elapse before driving CꢁVST high to exit full power-  
down mode. While in full power-down mode, the refer-  
ence is disabled to minimize power consumption. ꢀe  
sure to allow at least 2ms recovery time after exiting full  
power-down mode for the reference to settle. In  
partial/full power-down mode, maintain a logic low or a  
logic high on SCLK to minimize power consumption.  
Timing and Control  
Conversion-start and data-read operations are con-  
trolled by the CꢁVST and SCLK digital inputs. Figures 1  
and 5 show timing diagrams, which outline the serial-  
interface operation.  
A CꢁVST falling edge initiates a conversion sequence;  
the T/H stage holds the input voltage, the ADC begins  
to convert, and DOUT changes from high impedance to  
logic low. SCLK is used to drive the conversion  
process, and it shifts data out as each bit of the conver-  
sion is determined.  
SCLK begins shifting out the data after the 4th rising  
edge of SCLK. DOUT transitions t  
after each  
DOUT  
SCLK’s rising edge and remains valid 4ns (t  
)
DHOLD  
after the next rising edge. The 4th rising clock edge  
produces the MSꢀ of the conversion at DOUT, and the  
MSꢀ remains valid 4ns after the 5th rising edge. Since  
there are 12 data bits and 3 leading zeros, at least 16  
rising clock edges are needed to shift out these bits.  
For continuous operation, pull CꢁVST high between the  
14th and the 16th SCLK rising edges. If CꢁVST stays  
low after the falling edge of the 16th SCLK cycle, the  
DOUT line goes to a high-impedance state on either  
CꢁVST’s rising edge or the next SCLK’s rising edge.  
Transfer Function  
Figure 8 shows the unipolar transfer function for the  
MAX1277. Figure 9 shows the bipolar transfer function for  
the MAX1279. The MAX1277 output is straight binary,  
while the MAX1279 output is two’s complement.  
Applications Information  
Internal Reference  
The MAX1277/MAX1279 have an on-chip voltage refer-  
ence trimmed to 2.048V. The internal reference output  
is connected to REF and also drives the internal capac-  
itive DAC. The output can be used as a reference volt-  
age source for other components and can source up to  
2mA. ꢀypass REF with a 0.01µF capacitor and a 4.7µF  
capacitor to RGꢁD.  
Partial Power-Down and  
Full Power-Down Modes  
Power consumption can be reduced significantly by plac-  
ing the MAX1277/MAX1279 in either partial power-down  
mode or full power-down mode. Partial power-down  
mode is ideal for infrequent data sampling and fast wake-  
up time applications. Pull CꢁVST high after the 3rd SCLK  
rising edge and before the 14th SCLK rising edge to  
enter and stay in partial power-down mode (see Figure  
6). This reduces the supply current to 2mA. While in par-  
tial power-down mode, the reference remains enabled to  
allow valid conversions once the IC is returned to normal  
mode. Drive CꢁVST low and allow at least 14 SCLK  
cycles to elapse before driving CꢁVST high to exit partial  
power-down mode.  
The internal reference is continuously powered up dur-  
ing both normal and partial power-down modes. In full  
power-down mode, the internal reference is disabled.  
ꢀe sure to allow at least 2ms recovery time after hard-  
ware power-up or exiting full power-down mode for the  
reference to reach its intended value.  
EXECUTE PARTIAL POWER-DOWN TWICE  
SECOND 8-BIT TRANSFER  
CNVST  
FIRST 8-BIT TRANSFER  
SCLK  
DOUT ENTERS TRI-STATE ONCE CNVST GOES HIGH  
1ST SCLK RISING EDGE  
1ST SCLK RISING EDGE  
D8 D7  
DOUT  
0
0
0
D11  
D10  
D9  
0
0
0
0
0
0
0
0
MODE  
REF  
NORMAL  
PPD  
ENABLED (2.048V)  
RECOVERY  
FPD  
DISABLED  
Figure 7. SPI Interface—Full Power-Down Mode  
______________________________________________________________________________________ 11  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
How to Start a Conversion  
An analog-to-digital conversion is initiated by CꢁVST,  
OUTPUT CODE  
clocked by SCLK, and the resulting data is clocked out on  
DOUT by SCLK. With SCLK idling high or low, a falling  
FULL-SCALE  
111...111  
111...110  
TRANSITION  
edge on CꢁVST begins a conversion. This causes the  
analog input stage to transition from track to hold mode,  
and for DOUT to transition from high impedance to being  
actively driven low. A total of 16 SCLK cycles are required  
to complete a normal conversion. If CꢁVST is low during  
the 16th falling SCLK edge, DOUT returns to high imped-  
ance on the next rising edge of CꢁVST or SCLK, enabling  
the serial interface to be shared by multiple devices. If  
CꢁVST returns high after the 14th, but before the 16th  
SCLK rising edge, DOUT remains active so continuous  
conversions can be sustained. The highest throughput is  
achieved when performing continuous conversions. Figure  
10 illustrates a conversion using a typical serial interface.  
111...101  
FS = V  
REF  
ZS = 0  
V
REF  
1 LSB =  
4096  
000...011  
000...010  
000...001  
000...000  
Connection to  
Standard Interfaces  
The MAX1277/MAX1279 serial interface is fully compati-  
ble with SPI/QSPI and MICROWIRE (see Figure 11). If a  
serial interface is available, set the CPU’s serial interface  
in master mode so the CPU generates the serial clock.  
Choose a clock frequency up to 24MHz.  
/MAX1279  
0
1
2
3
FS  
FS - 3/2 LSB  
DIFFERENTIAL INPUT  
VOLTAGE (LSB)  
Figure 8. Unipolar Transfer Function (MAX1277 Only)  
SPI and MICROWIRE  
When using SPI or MICROWIRE, the MAX1277/ MAX1279  
are compatible with all four modes programmed with the  
CPHA and CPOL bits in the SPI or MICROWIRE control  
register. Conversion begins with a CꢁVST falling edge.  
DOUT goes low, indicating a conversion is in progress.  
Two consecutive 1-byte reads are required to get the full  
12 bits from the ADC. DOUT transitions on SCLK rising  
OUTPUT CODE  
V
FULL-SCALE  
TRANSITION  
REF  
2
FS =  
ZS = 0  
-V  
011...111  
011...110  
REF  
2
- FS =  
V
REF  
1 LSB =  
edges. DOUT is guaranteed to be valid t  
later and  
DOUT  
000...010  
000...001  
4096  
remains valid until t  
after the following SCLK rising  
DHOLD  
edge. When using CPOL = 0 and CPHA = 0, or CPOL = 1  
and CPHA = 1, the data is clocked into the µP on the fol-  
lowing rising edge. When using CPOL = 0 and CPHA = 1,  
or CPOL = 1 and CPHA = 0, the data is clocked into the  
µP on the next falling edge. See Figure 11 for connections  
and Figures 12 and 13 for timing. See the Timing  
Characteristics section to determine the best mode to use.  
000...000  
111...111  
111...110  
111...101  
QSPI  
Unlike SPI, which requires two 1-byte reads to acquire  
the 12 bits of data from the ADC, QSPI allows the mini-  
mum number of clock cycles necessary to clock in the  
data. The MAX1277/MAX1279 require 16 clock cycles  
from the µP to clock out the 12 bits of data. Figure 14  
shows a transfer using CPOL = 1 and CPHA = 1. The  
conversion result contains three zeros, followed by the  
12 data bits, and a trailing zero with the data in MSꢀ-  
100...001  
100...000  
-FS  
0
FS  
FS - 3/2 LSB  
DIFFERENTIAL INPUT  
VOLTAGE (LSB)  
Figure 9. ꢀipolar Transfer Function (MAX1279 Only)  
12 ______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
CNVST  
SCLK  
1
14  
16  
1
DOUT  
0
0
0
D11 D10  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
0
0
Figure 10. Continuous Conversion with ꢀurst/Continuous Clock  
I/O  
CNVST  
SCLK  
SCK  
MISO  
DOUT  
+3V TO +5V  
MAX1277  
MAX1279  
SS  
A) SPI  
CS  
CNVST  
SCLK  
SCK  
MISO  
DOUT  
+3V TO +5V  
MAX1277  
MAX1279  
SS  
B) QSPI  
I/O  
SK  
SI  
CNVST  
SCLK  
DOUT  
MAX1277  
MAX1279  
C) MICROWIRE  
Figure 11. Common Serial-Interface Connections to the MAX1277/MAX1279  
______________________________________________________________________________________ 13  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
CNVST  
8
9
16  
1
SCLK  
DOUT  
HIGH-Z  
HIGH-Z  
D11  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
D10  
D9  
Figure 12. SPI/MICROWIRE Serial-Interface Timing—Single Conversion (CPOL = CPHA = 0), (CPOL = CPHA = 1)  
CNVST  
SCLK  
DOUT  
14  
16  
1
1
/MAX1279  
0
0
0
D11  
D10  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
0
0
Figure 13. SPI/MICROWIRE Serial-Interface Timing—Continuous Conversion (CPOL = CPHA = 0), (CPOL = CPHA = 1)  
CNVST  
2
16  
SCLK  
DOUT  
HIGH-Z  
HIGH-Z  
D1  
D11  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D0  
D10 D9  
Figure 14. QSPI Serial-Interface Timing—Single Conversion (CPOL = 1, CPHA = 1)  
first format.  
For continuous conversion, set the serial port to trans-  
mit a clock, and pulse the frame sync signal for a clock  
period before data transmission. The serial-port config-  
uration (SPC) register should be set up with internal  
frame sync (TXM = 1), CLKX driven by an on-chip clock  
source (MCM = 1), burst mode (FSM = 1), and 16-bit  
word length (FO = 0).  
DSP Interface to the TMS320C54_  
The MAX1277/MAX1279 can be directly connected  
to the TMS320C54_ family of DSPs from Texas  
Instruments, Inc. Set the DSP to generate its own  
clocks or use external clock signals. Use either the  
standard or buffered serial port. Figure 15 shows the  
simplest interface between the MAX1277/MAX1279 and  
the TMS320C54_, where the transmit serial clock  
(CLKX) drives the receive serial clock (CLKR) and  
SCLK, and the transmit frame sync (FSX) drives the  
receive frame sync (FSR) and CꢁVST.  
This setup allows continuous conversions provided that  
the data transmit register (DXR) and the data-receive  
register (DRR) are serviced before the next conversion.  
Alternatively, autobuffering can be enabled when using  
the buffered serial port to execute conversions and  
14 ______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
read the data without CPU intervention. Connect the V  
Figure 16, where serial clock (CLOCK) drives the  
CLKR, and SCLK and the convert signal (COꢁVERT)  
drive the FSR and CꢁVST.  
L
pin to the TMS320C54_ supply voltage when the  
MAX1277/MAX1279 are operating with an analog sup-  
ply voltage higher than the DSP supply voltage. The  
word length can be set to 8 bits with FO = 1 to imple-  
ment the power-down modes. The CꢁVST pin must idle  
high to remain in either power-down state.  
The serial port must be set up to accept an external  
receive-clock and external receive-frame sync.  
The SPC register should be written as follows:  
TXM = 0, external frame sync  
Another method of connecting the MAX1277/MAX1279  
to the TMS320C54_ is to generate the clock signals  
external to either device. This connection is shown in  
MCM = 0, CLKX is taken from the CLKX pin  
FSM = 1, burst mode  
FO = 0, data transmitted/received as 16-bit words  
This setup allows continuous conversion, provided that  
the DRR is serviced before the next conversion.  
Alternatively, autobuffering can be enabled when using  
the buffered serial port to read the data without CPU  
V
L
DV  
DD  
MAX1277  
MAX1279  
TMS320C54_  
SCLK  
CLKX  
CLKR  
FSX  
intervention. Connect the V pin to the TMS320C54_  
L
supply voltage when the MAX1277/MAX1279 are oper-  
ating with an analog supply voltage higher than the  
DSP supply voltage.  
CNVST  
DOUT  
FSR  
The MAX1277/MAX1279 can also be connected to the  
TMS320C54_ by using the data transmit (DX) pin to  
drive CꢁVST and the CLKX generated internally to  
drive SCLK. A pullup resistor is required on the CꢁVST  
signal to keep it high when DX goes high impedance  
and 0001hex should be written to the DXR continuously  
for continuous conversions. The power-down modes  
may be entered by writing 00FFhex to the DXR (see  
Figures 17 and 18).  
DR  
Figure 15. Interfacing to the TMS320C54_ Internal Clocks  
V
L
DV  
DD  
MAX1277  
MAX1279  
TMS320C54_  
DSP Interface to the ADSP21_ _ _  
The MAX1277/MAX1279 can be directly connected to  
the ADSP21_ _ _ family of DSPs from Analog Devices,  
Inc. Figure 19 shows the direct connection of the  
MAX1277/MAX1279 to the ADSP21_ _ _. There are two  
modes of operation that can be programmed to interface  
with the MAX1277/MAX1279. For continuous conver-  
sions, idle CꢁVST low and pulse it high for one clock  
cycle during the LSꢀ of the previous transmitted word.  
The ADSP21_ _ _ STCTL and SRCTL registers should be  
SCLK  
CNVST  
DOUT  
CLKR  
FSR  
DR  
CLOCK  
CONVERT  
Figure 16. Interfacing to the TMS320C54_ External Clocks  
CNVST  
SCLK  
DOUT  
1
1
D0  
0
0
0
0
D11  
D10  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
0
0
Figure 17. DSP Interface—Continuous Conversion  
______________________________________________________________________________________ 15  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
CNVST  
SCLK  
DOUT  
1
1
0
0
0
0
0
D11 D10 D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
0
Figure 18. DSP Interface—Single-Conversion, Continuous/ꢀurst Clock  
ters should be configured for late framing (LAFR = 1)  
and for an active-low frame (LTFS = 1, LRFS = 1) signal.  
This is also the best way to enter the power-down modes  
by setting the word length to 8 bits (SLEꢁ = 1001).  
V
L
VDDINT  
TCLK  
RCLK  
TFS  
MAX1277  
MAX1279  
SCLK  
ADSP21_ _ _  
Connect the V pin to the ADSP21_ _ _ supply voltage  
L
when the MAX1277/MAX1279 are operating with a sup-  
ply voltage higher than the DSP supply voltage (see  
Figures 17 and 18).  
CNVST  
DOUT  
/MAX1279  
RFS  
DR  
Layout, Grounding, and Bypassing  
For best performance, use PC boards. Wire-wrap  
boards are not recommended. ꢀoard layout should  
ensure that digital and analog signal lines are separat-  
ed from each other. Do not run analog and digital  
(especially clock) lines parallel to one another, or digital  
lines underneath the ADC package.  
Figure 19. Interfacing to the ADSP21_ _ _  
SUPPLIES  
GND  
Figure 20 shows the recommended system ground  
connections. Establish a single-point analog ground  
(star ground point) at GꢁD, separate from the logic  
ground. Connect all other analog grounds and DGꢁD  
to this star ground point for further noise reduction. The  
ground return to the power supply for this ground  
should be low impedance and as short as possible for  
noise-free operation.  
V
L
10μF  
10μF  
0.1μF  
0.1μF  
High-frequency noise in the V  
power supply can  
DD  
affect the ADC’s high-speed comparator. ꢀypass this  
supply to the single-point analog ground with 0.01µF  
and 10µF bypass capacitors. Minimize capacitor lead  
lengths for best supply-noise rejection.  
V
DD  
V
L
GND RGND  
DGND  
V
L
DIGITAL  
CIRCUITRY  
MAX1277  
MAX1279  
Definitions  
Integral Nonlinearity  
Integral nonlinearity (IꢁL) is the deviation of the values on  
an actual transfer function from a straight line. This  
straight line can be either a best-straight-line fit or a line  
drawn between the end points of the transfer function,  
once offset and gain errors have been nullified. The static  
linearity parameters for the MAX1277/MAX1279 are mea-  
sured using the end-points method.  
Figure 20. Power-Supply Grounding Condition  
configured for early framing (LAFR = 0) and for an  
active-high frame (LTFS = 0, LRFS = 0) signal. In this  
mode, the data-independent frame-sync bit (DITFS = 1)  
can be selected to eliminate the need for writing to the  
transmit-data register more than once. For single conver-  
sions, idle CꢁVST high and pulse it low for the entire  
conversion. The ADSP21_ _ _ STCTL and SRCTL regis-  
16 ______________________________________________________________________________________  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
/MAX1279  
Differential Nonlinearity  
Differential nonlinearity (DꢁL) is the difference between  
an actual step width and the ideal value of 1 LSꢀ. A DꢁL  
error specification of 1 LSꢀ or less guarantees no missing  
codes and a monotonic transfer function.  
Total Harmonic Distortion  
Total harmonic distortion (THD) is the ratio of the RMS  
sum of the first five harmonics of the input signal to the  
fundamental itself. This is expressed as:  
2
2
2
2
V
+ V + V + V  
3 4 5  
Aperture Jitter  
2
THD = 20 x log  
Aperture jitter (t ) is the sample-to-sample variation in  
AJ  
V
1
the time between the samples.  
Aperture Delay  
where V is the fundamental amplitude, and V  
1
2
Aperture delay (t ) is the time defined between the  
AD  
through V are the amplitudes of the 2nd- through 5th-  
5
falling edge of CꢁVST and the instant when an actual  
sample is taken.  
order harmonics.  
Spurious-Free Dynamic Range  
Spurious-free dynamic range (SFDR) is the ratio of the  
RMS amplitude of the fundamental (maximum signal  
component) to the RMS value of the next largest distor-  
tion component.  
Signal-to-Noise Ratio  
For a waveform perfectly reconstructed from digital sam-  
ples, signal-to-noise ratio (SꢁR) is the ratio of the full-  
scale analog input (RMS value) to the RMS quantization  
error (residual error). The theoretical minimum analog-to-  
digital noise is caused by quantization error, and results  
directly from the ADC’s resolution (ꢁ bits):  
Full-Power Bandwidth  
Full-power bandwidth is the frequency at which the  
input signal amplitude attenuates by 3dꢀ for a full-scale  
input.  
SꢁR = (6.02 x ꢁ + 1.76)dꢀ  
In reality, there are other noise sources besides quantiza-  
tion noise, including thermal noise, reference noise, clock  
jitter, etc. Therefore, SꢁR is computed by taking the ratio  
of the RMS signal to the RMS noise, which includes all  
spectral components minus the fundamental, the first five  
harmonics, and the DC offset.  
Full-Linear Bandwidth  
Full-linear bandwidth is the frequency at which the sig-  
nal to noise plus distortion (SIꢁAD) is equal to 68dꢀ.  
Intermodulation Distortion (IMD)  
Any device with nonlinearities creates distortion prod-  
ucts when two sine waves at two different frequencies  
(f1 and f2) are input into the device. Intermodulation  
distortion (IMD) is the total power of the IM2 to IM5  
intermodulation products to the ꢁyquist frequency rela-  
tive to the total input power of the two input tones, f1  
and f2. The individual input tone levels are at -7dꢀFS.  
The intermodulation products are as follows:  
Signal-to-Noise Plus Distortion  
Signal-to-noise plus distortion (SIꢁAD) is the ratio of the  
fundamental input frequency’s RMS amplitude to the  
RMS equivalent of all other ADC output signals:  
SIꢁAD(dꢀ) = 20 x log (Signal  
/ ꢁoise  
)
RMS  
RMS  
Effective Number of Bits  
Effective number of bits (EꢁOꢀ) indicates the global  
accuracy of an ADC at a specific input frequency and  
sampling rate. An ideal ADC’s error consists of quantiza-  
tion noise only. With an input range equal to the full-scale  
range of the ADC, calculate the EꢁOꢀ as follows:  
• 2nd-order intermodulation products (IM2): f + f ,  
1
2
f - f  
2
1
• 3rd-order intermodulation products (IM3): 2f - f ,  
1
2
2f - f , 2f + f , 2f + f  
1
2
1
1
2
2
• 4th-order intermodulation products (IM4): 3f - f ,  
1
2
3f - f , 3f + f , 3f + f  
1
2
1
1
2
2
• 5th-order intermodulation products (IM5): 3f - 2f ,  
(SIꢁAD 1.76)  
EꢁOꢀ =  
1
2
3f - 2f , 3f + 2f , 3f + 2f  
1
2
1
1
2
2
6.02  
Package Information  
Chip Information  
TRAꢁSISTOR COUꢁT: 13,016  
For the latest package outline information and land patterns, go  
to www.maxim-ic.com/packages.  
PROCESS: ꢀiCMOS  
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.  
12 TQFꢁ  
T1244+3  
21-0139  
______________________________________________________________________________________ 17  
1.5Msps, Single-Supply, Low-Power, True-  
Differential, 12-Bit ADCs with Internal Reference  
Revision History  
REVISION  
NUMBER  
REVISION  
DATE  
PAGES  
CHANGED  
DESCRIPTION  
0
1
8/04  
4/09  
Initial release  
Removed commercial temperature grade parts from data sheet  
1–8  
/MAX1279  
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. ꢁo circuit patent licenses are  
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600  
© 2009 Maxim Integrated Products  
Maxim is a registered trademark of Maxim Integrated Products.  

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