MAX1295ACEI+ [MAXIM]

ADC, Successive Approximation, 12-Bit, 1 Func, 6 Channel, Parallel, Word Access, PDSO28, 0.150 INCH, QSOP-28;
MAX1295ACEI+
型号: MAX1295ACEI+
厂家: MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述:

ADC, Successive Approximation, 12-Bit, 1 Func, 6 Channel, Parallel, Word Access, PDSO28, 0.150 INCH, QSOP-28

光电二极管 转换器
文件: 总19页 (文件大小:403K)
中文:  中文翻译
下载:  下载PDF数据表文档文件
19-1530; Rev 3; 12/02  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
General Description  
Features  
The MAX1295/MAX1297 low-power, 12-bit analog-to-  
digital converters (ADCs) feature a successive-approxi-  
mation ADC, automatic power-down, fast wake-up  
(2µs), an on-chip clock, +2.5V internal reference, and a  
high-speed 12-bit parallel interface. They operate with  
a single +2.7V to +3.6V analog supply.  
12-Bit Resolution, ±±0. ꢀLB ꢀineꢁaitꢂ  
+3V Lingle-Lupplꢂ Opeaꢁtion  
Inteanꢁl +20.V Refeaence  
Loftwꢁae-Configuaꢁble Anꢁlog Input Multiplexea  
6-Chꢁnnel Lingle-Ended/  
Power consumption is only 5.4mW at the maximum  
sampling rate of 265ksps. Two software-selectable  
power-down modes enable the MAX1295/MAX1297 to  
be shut down between conversions; accessing the par-  
allel interface returns them to normal operation.  
Powering down between conversions can reduce sup-  
ply current below 10µA at lower sampling rates.  
3-Chꢁnnel Pseudo-Diffeaentiꢁl (MAX129.)  
2-Chꢁnnel Lingle-Ended/  
1-Chꢁnnel Pseudo-Diffeaentiꢁl (MAX1297)  
Loftwꢁae-Configuaꢁble Unipolꢁa/Bipolꢁa  
Anꢁlog Inputs  
ꢀow Cuaaent  
109mA (26.ksps)  
10±mA (1±±ksps)  
4±±µA (1±ksps)  
2µA (Lhutdown)  
Inteanꢁl 3MHz Full-Powea Bꢁndwidth Taꢁck/Hold  
Pꢁaꢁllel 12-Bit Inteafꢁce  
Both devices offer software-configurable analog inputs  
for unipolar/bipolar and single-ended/pseudo-differen-  
tial operation. In single-ended mode, the MAX1295 has  
six input channels and the MAX1297 has two (three  
input channels and one input channel, respectively,  
when in pseudo-differential mode).  
Excellent dynamic performance and low power, combined  
with ease of use and small package size, make these con-  
verters ideal for battery-powered and data-acquisition  
applications or for other circuits with demanding power-  
consumption and space requirements.  
Lmꢁll Footpaint  
28-Pin QLOP (MAX129.)  
24-Pin QLOP (MAX1297)  
The MAX1295/MAX1297 tri-states INT when CS goes high.  
Refer to MAX1265/MAX1267 if tri-stating INT is not desired.  
Pin Configurations  
The MAX1295 is offered in a 28-pin QSOP package, while  
the MAX1297 comes in a 24-pin QSOP. For pin-compati-  
ble +5V, 12-bit versions, refer to the MAX1294/MAX1296  
data sheet.  
TOP VIEW  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
1
2
3
4
5
6
7
8
9
28 D10  
27 D11  
26  
V
DD  
Applications  
Industrial Control Systems Data Logging  
25 REF  
24 REFADJ  
23 GND  
22 COM  
21 CH0  
20 CH1  
19 CH2  
18 CH3  
17 CH4  
16 CH5  
15 CS  
Energy Management  
Patient Monitoring  
Touchscreens  
MAX1295  
Data-Acquisition Systems  
Ordering Information  
INꢀ  
TEMP RANGE PIN-PACKAGE  
(ꢀLB)  
PART  
D0 10  
INT 11  
RD 12  
WR 13  
CLK 14  
MAX129.ACEI  
0°C to +70°C  
0°C to +70°C  
28 QSOP  
28 QSOP  
28 QSOP  
28 QSOP  
24 QSOP  
24 QSOP  
24 QSOP  
24 QSOP  
0.5  
1
MAX1295BCEI  
MAX1295AEEI -40°C to +85°C  
MAX1295BEEI -40°C to +85°C  
MAX1297ACEG 0°C to +70°C  
MAX1297BCEG 0°C to +70°C  
MAX1297AEEG -40°C to +85°C  
MAX1297BEEG -40°C to +85°C  
0.5  
1
0.5  
1
QLOP  
Pin Configurations continued at end of data sheet.  
0.5  
1
Typical Operating Circuits appear at end of data sheet.  
________________________________________________________________ Maxim Integrated Products  
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at  
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
ABLOꢀUTE MAXIMUM RATINGL  
DD  
CH0–CH5, COM to GND............................-0.3V to (V  
REF, REFADJ to GND.................................-0.3V to (V  
Digital Inputs to GND ...............................................-0.3V to +6V  
V
to GND..............................................................-0.3V to +6V  
28-Pin QSOP (derate 8.00mW/°C above +70°C)........667mW  
Operating Temperature Ranges  
MAX1295_C_ _/MAX1297_C_ _ ........................0°C to +70°C  
MAX1295_E_ _/MAX1297_E_ _ ......................-40°C to +85°C  
Storage Temperature Range.............................-65°C to +150°C  
Lead Temperature (soldering, 10s) .................................+300°C  
+ 0.3V)  
+ 0.3V)  
DD  
DD  
Digital Outputs (D0–D11, INT) to GND.......-0.3V to (V + 0.3V)  
DD  
Continuous Power Dissipation (T = +70°C)  
A
24-Pin QSOP (derate 9.5mW/°C above +70°C)..........762mW  
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.  
EꢀECTRICAꢀ CHARACTERILTICL  
DD  
(V  
= +2.7V to +3.6V, COM = GND, REFADJ = V , V  
= +2.5V, 4.7µF capacitor at REF pin, f  
= 4.8MHz (50% duty cycle),  
CLK  
DD REF  
T
A
= T  
to T  
, unless otherwise noted. Typical values are at T = +25°C.)  
MIN  
MAX  
A
PARAMETER  
LYMBOꢀ  
CONDITIONL  
MIN  
12  
TYP  
MAX  
UNITL  
DC ACCURACY (Note 1)  
Resolution  
RES  
INL  
Bits  
MAX129_A  
MAX129_B  
No missing codes over temperature  
0.5  
1
Relative Accuracy (Note 2)  
LSB  
Differential Nonlinearity  
Offset Error  
DNL  
1
LSB  
LSB  
4
Gain Error (Note 3)  
Gain Temperature Coefficient  
4
LSB  
2.0  
0.2  
ppm/°C  
Channel-to-Channel Offset  
Matching  
LSB  
DYNAMIC LPECIFICATIONL (f  
= 50kHz, V = 2.5V , 265ksps, external f  
= 4.8MHz, bipolar input mode)  
P-P  
IN(sine-wave)  
SINAD  
IN  
CLK  
Signal-to-Noise Plus Distortion  
67  
80  
70  
dB  
dB  
Total Harmonic Distortion  
(including 5th-order harmonic)  
THD  
-78  
Spurious-Free Dynamic Range  
Intermodulation Distortion  
Channel-to-Channel Crosstalk  
Full-Linear Bandwidth  
SFDR  
IMD  
dB  
dB  
f
f
= 49kHz, f  
= 52kHz  
IN2  
76  
-78  
250  
3
IN1  
= 125kHz (Note 4)  
dB  
IN  
SINAD > 68dB  
-3dB rolloff  
kHz  
MHz  
Full-Power Bandwidth  
CONVERLION RATE  
External clock mode  
3.3  
2.5  
3.2  
Conversion Time (Note 5)  
t
External acquisition/internal clock mode  
Internal acquisition/internal clock mode  
3.0  
3.6  
3.5  
4.1  
625  
µs  
CONV  
Track/Hold Acquisition Time  
Aperture Delay  
t
ns  
ns  
ACQ  
External acquisition or external clock mode  
External acquisition or external clock mode  
Internal acquisition/internal clock mode  
50  
<50  
<200  
Aperture Jitter  
ps  
External Clock Frequency  
Duty Cycle  
f
0.1  
30  
4.8  
70  
MHz  
%
CLK  
2
_______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
EꢀECTRICAꢀ CHARACTERILTICL (continued)  
(V  
= +2.7V to +3.6V, COM = GND, REFADJ = V , V  
= +2.5V, 4.7µF capacitor at REF pin, f  
= 4.8MHz (50% duty cycle),  
CLK  
DD  
DD REF  
T
A
= T  
to T  
, unless otherwise noted. Typical values are at T = +25°C.)  
MIN  
MAX  
A
PARAMETER  
LYMBOꢀ  
CONDITIONL  
MIN  
TYP  
MAX  
UNITL  
ANAOGINPUTL
Analog Input Voltage Range  
Single-Ended and Differential  
(Note 6)  
Unipolar, V  
= 0  
0
REF  
V
+V  
COM  
REF  
REF  
V
IN  
V
Bipolar, V  
= V  
/ 2  
-V  
/2  
/2  
COM  
REF  
Multiplexer Leakage Current  
Input Capacitance  
On/off-leakage-current, V = 0 or V  
IN  
0.01  
12  
1
µA  
pF  
DD  
C
IN  
INTERNAꢀ REFERENCE  
REF Output Voltage  
2.49  
2.5  
15  
2.51  
V
mA  
REF Short-Circuit Current  
REF Temperature Coefficient  
REFADJ Input Range  
TC  
20  
ppm/°C  
mV  
REF  
For small adjustments  
100  
REFADJ High Threshold  
Load Regulation (Note 7)  
Capacitive Bypass at REFADJ  
Capacitive Bypass at REF  
EXTERNAꢀ REFERENCE AT REF  
To power down the internal reference  
0 to 0.5mA output load  
V
- 1  
V
DD  
0.2  
mV/mA  
µF  
0.01  
1
4.7  
10  
µF  
V
+
DD  
REF Input Voltage Range  
REF Input Current  
V
V
REF  
1.0  
2.0  
50mV  
V
= 2.5V, f  
= 265ksps  
SAMPLE  
200  
300  
2
REF  
I
µA  
REF  
Shutdown mode  
DIGITAꢀ INPUTL AND OUTPUTL  
Input Voltage High  
V
V
V
IH  
Input Voltage Low  
V
0.8  
1
IL  
Input Hysteresis  
V
HYS  
200  
0.1  
15  
mV  
µA  
pF  
V
Input Leakage Current  
Input Capacitance  
I
V
= 0 or V  
DD  
IN  
IN  
C
IN  
OL  
OH  
Output Voltage Low  
Output Voltage High  
V
I
I
= 1.6mA  
0.4  
1
SINK  
V
= 1mA  
V
- 0.5  
V
SOURCE  
DD  
Three-State Leakage Current  
Three-State Output Capacitance  
POWER REQUIREMENTL  
Analog Supply Voltage  
I
0.1  
15  
µA  
pF  
CS = V  
CS = V  
LEAKAGE  
DD  
DD  
C
OUT  
V
2.7  
3.6  
2.8  
2.3  
1.2  
0.8  
10  
V
DD  
Internal reference  
External reference  
Internal reference  
External reference  
2.5  
1.9  
0.9  
0.5  
2
Operating mode,  
= 265ksps  
f
SAMPLE  
mA  
Positive Supply Current  
Power-Supply Rejection  
I
DD  
Standby mode  
Shutdown mode  
µA  
PSR  
V
= 2.7V to 3.6V, full-scale input  
0.4  
0.9  
mV  
DD  
_______________________________________________________________________________________  
3
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
TIMING CHARACTERILTICL  
DD  
(V  
= +2.7V to +3.6V, COM = GND, REFADJ = V , V  
= +2.5V, 4.7µF capacitor at REF pin, f  
= 4.8MHz (50% duty cycle),  
DD REF  
CLK  
T
A
= T  
to T  
, unless otherwise noted. Typical values are at T = +25°C.)  
MIN  
MAX  
A
PARAMETER  
LYMBOꢀ  
CONDITIONL  
MIN  
TYP  
MAX  
UNITL  
ns  
CLK Period  
t
208  
40  
40  
40  
0
CP  
CH  
CLK Pulse Width High  
t
ns  
CLK Pulse Width Low  
t
ns  
CL  
DS  
t
t
ns  
Data Valid to WR Rise Time  
WR Rise to Data Valid Hold Time  
WR to CLK Fall Setup Time  
CLK Fall to WR Hold Time  
CS to CLK or WR Setup Time  
CLK or WR to CS Hold Time  
CS Pulse Width  
ns  
DH  
t
t
40  
40  
60  
0
ns  
CWS  
ns  
CWH  
t
ns  
CSWS  
t
ns  
CSWH  
t
100  
60  
20  
20  
20  
ns  
CS  
t
ns  
WR Pulse Width (Note 8)  
CS Rise to Output Disable  
RD Rise to Output Disable  
RD Fall to Output Data Valid  
RD Fall to INT High Delay  
CS Fall to Output Data Valid  
WR  
t
C
C
C
C
C
= 20pF, Figure 1  
100  
70  
ns  
TC  
LOAD  
LOAD  
LOAD  
LOAD  
LOAD  
t
TR  
= 20pF, Figure 1  
= 20pF, Figure 1  
= 20pF, Figure 1  
= 20pF, Figure 1  
ns  
t
70  
ns  
DO  
t
100  
110  
ns  
INT1  
t
ns  
DO2  
Note 1: Tested at V  
= +3V, COM = GND, unipolar single-ended input mode.  
DD  
Note 2: Relative accuracy is the deviation of the analog value at any code from its theoretical value after offset and gain errors have  
been removed.  
Note 3: Offset nulled.  
Note 4: On channel is grounded; sine wave applied to off channels.  
Note .: Conversion time is defined as the number of clock cycles times the clock period; clock has a 50% duty cycle.  
Note 6: Input voltage range referenced to negative input. The absolute range for the analog inputs is from GND to V  
Note 7: External load should not change during conversion for specified accuracy.  
.
DD  
Note 8: When bit 5 is set low for internal acquisition, WR must not return low until after the first falling clock edge of the conversion.  
V
DD  
DOUT  
3kΩ  
C
20pF  
LOAD  
6kΩ  
DOUT  
C
LOAD  
20pF  
a) HIGH-Z TO V AND V TO V  
OH  
b) HIGH-Z TO V AND V TO V  
OL  
OH  
OL  
OL  
OH  
Figure 1. Load Circuits for Enable/Disable Times  
4
_______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Typical Operating Characteristics  
(V  
= +3V, V  
= +2.500V, f  
= 4.8MHz, C = 20pF, T = +25°C, unless otherwise noted.)  
DD  
REF  
CLK  
L
A
DIFFERENTIAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE  
SUPPLY CURRENT  
vs. SAMPLE FREQUENCY  
INTEGRAL NONLINEARITY  
vs. DIGITAL OUTPUT CODE  
0.5  
0.4  
0.5  
10,000  
1000  
100  
10  
0.4  
0.3  
0.3  
WITH INTERNAL REFERENCE  
0.2  
0.2  
0.1  
0.1  
0
0
-0.1  
-0.2  
-0.3  
-0.4  
-0.5  
-0.1  
-0.2  
-0.3  
-0.4  
-0.5  
WITH EXTERNAL REFERENCE  
0
1k  
0
1000  
2000  
3000  
4000  
5000  
0.1  
1
10  
100  
10k 100k 1M  
0
1000  
2000  
3000  
4000  
5000  
DIGITAL OUTPUT CODE  
f
(Hz)  
DIGITAL OUTPUT CODE  
SAMPLE  
SUPPLY CURRENT vs. SUPPLY VOLTAGE  
STANDBY CURRENT vs. SUPPLY VOLTAGE  
SUPPLY CURRENT vs. TEMPERATURE  
2.10  
2.05  
2.00  
1.95  
1.90  
1.85  
1.80  
930  
920  
910  
900  
890  
880  
2.2  
2.1  
2.0  
1.9  
1.8  
1.7  
1.6  
R = ∞  
R = ∞  
L
L
CODE = 101010100000  
CODE = 101010100000  
2.7  
3.0  
3.3  
3.6  
2.7  
3.0  
3.3  
3.6  
-40  
-15  
10  
35  
60  
85  
V
(V)  
V
(V)  
DD  
TEMPERATURE (°C)  
DD  
STANDBY CURRENT  
vs. TEMPERATURE  
POWER-DOWN CURRENT  
vs. SUPPLY VOLTAGE  
POWER-DOWN CURRENT  
vs. TEMPERATURE  
1.50  
1.25  
1.00  
1.2  
1.1  
1.0  
0.9  
0.8  
930  
920  
910  
900  
890  
880  
0.75  
0.50  
2.7  
3.0  
3.3  
3.6  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
V
(V)  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
DD  
_______________________________________________________________________________________  
.
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Typical Operating Characteristics (continued)  
(V  
= +3V, V  
= +2.500V, f  
= 4.8MHz, C = 20pF, T = +25°C, unless otherwise noted.)  
DD  
REF  
CLK  
L
A
INTERNAL REFERENCE VOLTAGE  
vs. TEMPERATURE  
INTERNAL REFERENCE VOLTAGE  
vs. SUPPLY VOLTAGE  
OFFSET ERROR vs. SUPPLY VOLTAGE  
2.53  
2.53  
0
-0.5  
-1.0  
-1.5  
-2.0  
-2.5  
2.52  
2.51  
2.50  
2.49  
2.48  
2.52  
2.51  
2.50  
2.49  
2.48  
3.0  
3.3  
-40  
-15  
10  
35  
60  
85  
2.7  
3.6  
2.7  
3.0  
3.3  
3.6  
TEMPERATURE (°C)  
V
(V)  
V
(V)  
DD  
DD  
GAIN ERROR vs. TEMPERATURE  
OFFSET ERROR vs. TEMPERATURE  
GAIN ERROR vs. SUPPLY VOLTAGE  
0.5  
0
0.5  
0
1.0  
0
-0.5  
-1.0  
-1.5  
-2.0  
-2.5  
-0.5  
-1.0  
-1.5  
-2.0  
-1.0  
-2.0  
-3.0  
-40  
-15  
10  
35  
60  
85  
-40  
-15  
10  
35  
60  
85  
2.7  
3.0  
3.3  
3.6  
TEMPERATURE (°C)  
TEMPERATURE (°C)  
V
(V)  
DD  
FFT PLOT  
20  
0
V
f
= 3V  
= 50kHz  
DD  
IN  
f
= 250ksps  
SAMPLE  
-20  
-40  
-60  
-80  
-100  
-120  
-140  
0
200  
400  
600  
800  
1000  
FREQUENCY (kHz)  
6
_______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Pin Description  
PIN  
NAME  
FUNCTION  
MAX129.  
MAX1297  
1
2
1
2
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
D0  
INT  
Three-State Digital Output (D9)  
Three-State Digital Output (D8)  
Three-State Digital I/O Line (D7)  
Three-State Digital I/O Line (D6)  
Three-State Digital I/O Line (D5)  
Three-State Digital I/O Line (D4)  
Three-State Digital I/O Line (D3)  
Three-State Digital I/O Line (D2)  
Three-State Digital I/O Line (D1)  
Three-State Digital I/O Line (D0)  
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10  
11  
10  
11  
INT goes low when the conversion is complete and output data is ready.  
Active-Low Read Select. If CS is low, a falling edge on RD enables the read  
operation on the data bus.  
12  
12  
RD  
Active-Low Write Select. When CS is low in the internal acquisition mode, a rising  
edge on WR latches in configuration data and starts an acquisition plus a conver-  
sion cycle. When CS is low in external acquisition mode, the first rising edge on WR  
ends acquisition and starts a conversion.  
13  
13  
WR  
Clock Input. In external clock mode, drive CLK with a TTL/CMOS-compatible clock.  
14  
15  
14  
15  
CLK  
In internal clock mode, connect this pin to either V  
or GND.  
DD  
Active-Low Chip Select. When CS is high, digital outputs (INT, D11–D0) are high  
impedance.  
CS  
16  
17  
18  
19  
20  
21  
16  
17  
CH5  
CH4  
CH3  
CH2  
CH1  
CH0  
Analog Input Channel 5  
Analog Input Channel 4  
Analog Input Channel 3  
Analog Input Channel 2  
Analog Input Channel 1  
Analog Input Channel 0  
Ground Reference for Analog Inputs. Sets zero-code voltage in single-ended mode  
and must be stable to 0.5 LSB during conversion.  
22  
23  
18  
19  
COM  
GND  
Analog and Digital Ground  
Bandgap Reference Output/Bandgap Reference Buffer Input. Bypass to GND with  
24  
20  
REFADJ  
a 0.01µF capacitor. When using an external reference, connect REFADJ to V  
to  
DD  
disable the internal bandgap reference.  
_______________________________________________________________________________________  
7
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Pin Description (continued)  
PIN  
NAME  
FUNCTION  
MAX129.  
MAX1297  
Bandgap Reference Buffer Output/External Reference Input. Add a 4.7µF capacitor  
to GND when using the internal reference.  
25  
21  
REF  
26  
27  
28  
22  
23  
24  
V
Analog +2.7V to +3.6V Power Supply. Bypass with a 0.1µF capacitor to GND.  
Three-State Digital Output (D11)  
DD  
D11  
D10  
Three-State Digital Output (D10)  
REF  
REFADJ  
17kΩ  
1.22V  
REFERENCE  
A =  
V
2.05  
(CH5)  
(CH4)  
(CH3)  
(CH2)  
CH1  
ANALOG  
INPUT  
MULTIPLEXER  
T/H  
CHARGE REDISTRIBUTION  
12-BIT DAC  
COMP  
CH0  
12  
SUCCESSIVE-  
APPROXIMATION  
REGISTER  
COM  
CLK  
CLOCK  
CS  
WR  
RD  
CONTROL LOGIC  
&
MAX1295  
MAX1297  
LATCHES  
INT  
V
DD  
12  
THREE-STATE, BIDIRECTIONAL  
I/O INTERFACE  
GND  
D0–D11  
12-BIT DATA BUS  
( ) ARE FOR MAX1295 ONLY.  
Figure 2. Simplified Functional Diagram of 6-/2-Channel MAX1295/MAX1297  
Single-Ended and  
_______________Detailed Description  
Pseudo-Differential Operation  
The sampling architecture of the ADC’s analog com-  
parator is illustrated in the equivalent input circuit in  
Figure 3. In single-ended mode, IN+ is internally  
switched to channels CH0–CH5 for the MAX1295  
(Figure 3a) and to CH0–CH1 for the MAX1297 (Figure  
3b), while IN- is switched to COM (Table 2). In differen-  
tial mode, IN+ and IN- are selected from analog input  
pairs (Table 3) and are internally switched to either of  
Converter Operation  
The MAX1295/MAX1297 ADCs use a successive-  
approximation (SAR) conversion technique and an input  
track/hold (T/H) stage to convert an analog input signal  
to a 12-bit digital output. This output format provides an  
easy interface to standard microprocessors (µPs). Figure  
2 shows the simplified internal architecture of the  
MAX1295/MAX1297.  
8
_______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
the analog inputs. This configuration is pseudo-differ-  
ential in that only the signal at IN+ is sampled. The  
return side (IN-) must remain stable within 0.5 LSB  
( 0.1 LSB for best performance) with respect to GND  
during a conversion. To accomplish this, connect a  
0.1µF capacitor from IN- (the selected input) to GND.  
end of the acquisition interval, the T/H switch opens,  
retaining charge on C  
at IN+.  
as a sample of the signal  
HOLD  
The conversion interval begins with the input multiplex-  
er switching C from the positive input (IN+) to the  
HOLD  
negative input (IN-). This unbalances node ZERO at  
the comparator’s positive input. The capacitive digital-  
to-analog converter (DAC) adjusts during the remain-  
During the acquisition interval, the channel selected as  
the positive input (IN+) charges capacitor C . At the  
HOLD  
12-BIT CAPACITIVE DAC  
12-BIT CAPACITIVE DAC  
V
REF  
V
REF  
COMPARATOR  
INPUT  
MUX  
COMPARATOR  
INPUT  
MUX  
C
HOLD  
C
HOLD  
ZERO  
+
ZERO  
+
CH0  
CH0  
CH1  
12pF  
12pF  
R
IN  
CH1  
CH2  
CH3  
CH4  
CH5  
R
IN  
800Ω  
800Ω  
C
SWITCH  
C
SWITCH  
HOLD  
HOLD  
TRACK  
TRACK  
AT THE SAMPLING INSTANT,  
THE MUX INPUT SWITCHES  
FROM THE SELECTED IN+  
CHANNEL TO THE SELECTED  
IN- CHANNEL.  
AT THE SAMPLING INSTANT,  
THE MUX INPUT SWITCHES  
FROM THE SELECTED IN+  
CHANNEL TO THE SELECTED  
IN- CHANNEL.  
T/H  
SWITCH  
T/H  
SWITCH  
COM  
COM  
SINGLE-ENDED MODE: IN+ = CH0–CH5, IN- = COM  
DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIRS OF  
CH0/CH1 AND CH2/CH3, AND CH4/CH5  
SINGLE-ENDED MODE: IN+ = CH0–CH1, IN- = COM  
DIFFERENTIAL MODE: IN+ AND IN- SELECTED FROM PAIR  
CH0/CH1  
Figure 3a. MAX1295 Simplified Input Structure  
Figure 3b. MAX1297 Simplified Input Structure  
Tꢁble 10 Contaol-Bꢂte Functionꢁl Descaiption  
BIT  
NAME  
FUNCTIONAꢀ DELCRIPTION  
PD1 and PD± select the various clock and power-down modes.  
±
±
1
1
±
1
±
1
Full Power-Down Mode. Clock mode is unaffected.  
D7, D6  
PD1, PD0  
Standby Power-Down Mode. Clock mode is unaffected.  
Normal Operation Mode. Internal clock mode selected.  
Normal Operation Mode. External clock mode selected.  
ACQMOD = 0: Internal Acquisition Mode  
ACQMOD = 1: External Acquisition Mode  
D5  
D4  
ACQMOD  
SGL/DIF = 0: Pseudo-Differential Analog Input Mode  
SGL/DIF = 1: Single-Ended Analog Input Mode  
In single-ended mode, input signals are referred to COM. In differential mode, the voltage difference  
between two channels is measured (Tables 2, 4).  
SGL/DIF  
UNI/BIP = 0: Bipolar Mode  
UNI/BIP = 1: Unipolar Mode  
In unipolar mode, an analog input signal from 0V to V  
D3  
UNI/BIP  
can be converted; in bipolar mode, the  
REF  
signal can range from -V /2 to +V /2.  
REF REF  
Address bits A2, A1, A0 select which of the 6/2 (MAX1295/MAX1297) channels is to be converted  
(Tables 2, 3).  
D2, D1, D0  
A2, A1, A0  
_______________________________________________________________________________________  
9
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Tꢁble 20 Chꢁnnel Lelection foa Lingle-Ended Opeaꢁtion (LGꢀ/DIF = 1)  
A2  
A1  
A±  
CH±  
CH1  
CH2*  
CH3*  
CH4*  
CH.*  
COM  
0
0
0
0
1
1
0
0
1
1
0
0
0
1
0
1
0
1
+
-
-
-
-
-
-
+
+
+
+
+
*Channels CH2–CH5 apply to MAX1295 only.  
Tꢁble 30 Chꢁnnel Lelection foa Pseudo-Diffeaentiꢁl Opeaꢁtion (LGꢀ/DIF = ±)  
A2  
0
A1  
0
A±  
0
CH±  
CH1  
CH2*  
CH3*  
CH4*  
CH.*  
+
-
-
0
0
1
+
0
1
0
+
-
-
0
1
1
+
1
0
0
+
-
-
1
0
1
+
*Channels CH2–CH5 apply to MAX1295 only.  
der of the conversion cycle to restore node ZERO to 0V  
within the limits of 12-bit resolution. This action is equiv-  
In single-ended operation, IN- is connected to COM  
and the converter samples the positive “+” input. In  
pseudo-differential operation, IN- connects to the nega-  
alent to transferring a 12pF (V  
- V ) charge from  
IN-  
IN+  
C
HOLD  
to the binary-weighted capacitive DAC, which in  
tive “-” input, and the difference of (IN+) - (IN-) is sam-  
| |  
turn forms a digital representation of the analog input  
signal.  
pled. At the beginning of the next conversion, the  
positive input connects back to IN+ and CHOLD  
charges to the input signal.  
Analog Input Protection  
Internal protection diodes, which clamp the analog  
The time required for the T/H stage to acquire an input  
signal depends on how quickly its input capacitance is  
charged. If the input signal’s source impedance is high,  
the acquisition time lengthens and more time must be  
allowed between conversions. The acquisition time,  
input to V  
and GND, allow each input channel to  
DD  
swing within (GND - 300mV) to (V  
+ 300mV) without  
DD  
damage. However, for accurate conversions near full  
scale, both inputs must not exceed (V  
less than (GND - 50mV).  
+ 50mV) or be  
DD  
t
, is the maximum time the device takes to acquire  
ACQ  
the signal, and is also the minimum time required for  
the signal to be acquired. Calculate this with the follow-  
ing equation:  
If an analog input voltage exceeds the supplies by  
more than 50mV, limit the forward-bias input current to  
4mA.  
t
= 9 (R + R ) C  
S IN IN  
ACQ  
Track/Hold  
The MAX1295/MAX1297 T/H stage enters its tracking  
mode on WR’s rising edge. In external acquisition  
mode, the part enters its hold mode on the next rising  
edge of WR. In internal acquisition mode, the part  
enters its hold mode on the fourth falling edge of clock  
after writing the control byte. Note that, in internal clock  
mode, this is approximately 1µs after writing the control  
byte.  
where R is the source impedance of the input signal,  
S
R
(800) is the input resistance, and C (12pF) is  
IN  
IN  
the input capacitance of the ADC. Source impedances  
below 3khave no significant impact on the MAX1295/  
MAX1297’s AC performance.  
Higher source impedances can be used if a 0.01µF  
capacitor is connected to the individual analog inputs.  
1± ______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
t
CS  
CS  
t
t
t
CSWS  
ACQ  
CONV  
t
t
CSWH  
WR  
WR  
t
DH  
t
DS  
CONTROL  
BYTE  
D7–D0  
ACQMOD = "0"  
HIGH-Z  
HIGH-Z  
INT  
RD  
t
INT1  
t
TR  
t
D0  
HIGH-Z  
HIGH-Z  
DOUT  
DATA VALID  
Figure 4. Conversion Timing Using Internal Acquisition Mode  
Together with the input impedance, this capacitor  
forms an RC filter, limiting the ADC’s signal bandwidth.  
for acquiring the signal: an internal and an external  
acquisition. The conversion period lasts for 13 clock  
cycles in either the internal or external clock or acquisi-  
tion mode. Writing a new control byte during a conver-  
sion cycle aborts the conversion and starts a new  
acquisition interval.  
Input Bandwidth  
The MAX1295/MAX1297 T/H stage offers a 250kHz full-  
linear and a 3MHz full-power bandwidth. This makes it  
possible to digitize high-speed transients 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 fre-  
quency band of interest, anti-alias filtering is recom-  
mended.  
Internal Acquisition  
Select internal acquisition by writing the control byte  
with the ACQMOD bit cleared (ACQMOD = 0). This  
causes the write pulse to initiate an acquisition interval  
whose duration is internally timed. Conversion starts  
when this acquisition interval (three external clock  
cycles or approximately 1µs in internal clock mode)  
ends (Figure 4). Note that, when the internal acquisition  
is combined with the internal clock, the aperture jitter  
can be as high as 200ps. Internal clock users wishing  
to achieve the 50ps jitter specification should always  
use external acquisition mode.  
Starting a Conversion  
Initiate a conversion by writing a control byte that selects  
the multiplexer channel and configures the MAX1295/  
MAX1297 for either unipolar or bipolar operation. A  
write pulse (WR + CS) can either start an acquisition  
interval or initiate a combined acquisition plus conver-  
sion. The sampling interval occurs at the end of the  
acquisition interval. The acquisition mode (ACQMOD)  
bit in the input control byte (Table 1) offers two options  
______________________________________________________________________________________ 11  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
t
CS  
CS  
t
CSWS  
t
t
CONV  
ACQ  
t
CSHW  
t
WR  
WR  
t
DH  
t
t
DS  
DH  
CONTROL  
BYTE  
ACQMOD = "1"  
CONTROL  
BYTE  
ACQMOD = "0"  
D7–D0  
INT  
HIGH-Z  
HIGH-Z  
t
INT1  
RD  
t
D0  
t
TR  
HIGH-Z  
HIGH-Z  
DOUT  
DATA VALID  
Figure 5. Conversion Timing Using External Acquisition Mode  
External Acquisition  
when the conversion is complete and the output data is  
ready (Figures 4 and 5). It returns high on the first read  
cycle or if a new control byte is written.  
Use external acquisition mode for precise control of the  
sampling aperture and/or dependent control of acquisi-  
tion and conversion times. The user controls acquisition  
and start-of-conversion with two separate write pulses.  
The first pulse, written with ACQMOD = 1, starts an  
acquisition interval of indeterminate length. The second  
write pulse, written with ACQMOD = 0 (all other bits in  
control byte unchanged), terminates acquisition and  
starts conversion on WR rising edge (Figure 5).  
Selecting Clock Mode  
The MAX1295/MAX1297 operate with either an internal  
or an external clock. Control bits D6 and D7 select  
either internal or external clock mode. The part retains  
the last-requested clock mode if a power-down mode is  
selected in the current input word. For both internal and  
external clock mode, internal or external acquisition  
can be used. At power-up, the MAX1295/MAX1297  
enter the default external clock mode.  
The address bits for the input multiplexer must have the  
same values on the first and second write pulse.  
Power-down mode bits (PD0, PD1) can assume new  
values on the second write pulse (see Power-Down  
Modes section). Changing other bits in the control byte  
corrupts the conversion.  
Internal Clock Mode  
Select internal clock mode to release the µP from the  
burden of running the SAR conversion clock. Bit D7 of  
the control byte must be set to 1 and bit D6 must be set  
to 0. The internal clock frequency is then selected,  
resulting in a conversion time of 3.6µs. When using the  
internal clock mode, tie the CLK pin either high or low  
to prevent the pin from floating.  
Reading a Conversion  
A standard interrupt signal INT is provided to allow the  
MAX1295/MAX1297 to flag the µP when the conversion  
has ended and a valid result is available. INT goes low  
12 ______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
ACQUISITION STARTS  
CONVERSION STARTS  
ACQUISITION ENDS  
t
CP  
CLK  
WR  
t
t
CH  
t
CWS  
CL  
WR GOES HIGH WHEN CLK IS HIGH.  
ACQMOD = "0"  
ACQUISITION STARTS  
t
CWH  
CONVERSION STARTS  
ACQUISITION ENDS  
CLK  
WR  
ACQMOD = "0"  
WR GOES HIGH WHEN CLK IS LOW.  
Figure 6a. External Clock and WR Timing (Internal Acquisition Mode)  
ACQUISITION STARTS  
ACQUISITION ENDS  
CONVERSION STARTS  
CLK  
t
CWS  
t
DH  
WR  
ACQMOD = "0"  
ACQMOD = "1"  
WR GOES HIGH WHEN CLK IS HIGH  
ACQUISITION ENDS  
ACQUISITION STARTS  
CONVERSION STARTS  
CLK  
WR  
t
CWH  
t
DH  
ACQMOD = "1"  
WR GOES HIGH WHEN CLK IS LOW  
ACQMOD = "0"  
Figure 6b. External Clock and WR Timing (External Acquisition Mode)  
External Clock Mode  
To select the external clock mode, bits D6 and D7 of  
the control byte must be set to 1. Figure 6 shows the  
clock and WR timing relationship for internal (Figure 6a)  
and external (Figure 6b) acquisition modes with an  
external clock. For proper operation, a 100kHz to  
4.8MHz clock frequency with 30% to 70% duty cycle is  
recommended. Operating the MAX1295/MAX1297 with  
clock frequencies lower than 100kHz is not recommend-  
ed because the resulting voltage droop across the hold  
capacitor in the T/H stage degrades performance.  
Digital Interface  
The input and output data are multiplexed on a three-  
state parallel interface (I/O) that can easily be inter-  
faced with standard µPs. The signals CS, WR, and RD  
control the write and read operations. CS represents  
______________________________________________________________________________________ 13  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Tꢁble 40 Contaol-Bꢂte Foamꢁt  
D7  
(MLB)  
D±  
(ꢀLB)  
D6  
D.  
D4  
D3  
D2  
D1  
PD1  
PD0  
ACQMOD  
A2  
A1  
A0  
SGL/DIF  
UNI/BIP  
An internal buffer is designed to provide +2.5V at REF for  
both the MAX1295 and MAX1297. The internally trimmed  
+1.22V reference is buffered with a +2.05V/V gain.  
V
= +3V  
DD  
50kΩ  
50kΩ  
Internal Reference  
The full-scale range with the internal reference is +2.5V  
with unipolar inputs and 1.25V with bipolar inputs. The  
internal reference buffer allows for small adjustments  
( 100mV) in the reference voltage (Figure 7).  
MAX1295  
MAX1297  
330kΩ  
REFADJ  
REF  
GND  
0.01µF  
4.7µF  
Note: The reference buffer must be compensated with  
an external capacitor (4.7µF min) connected between  
REF and GND to reduce reference noise and switching  
spikes from the ADC. To further minimize noise on the  
reference, connect a 0.01µF capacitor between REFADJ  
and GND.  
GND  
Figure 7. Reference Adjustment with External Potentiometer  
the chip-select signal, which enables a µP to address  
the MAX1295/MAX1297 as an I/O port. When high, CS  
disables the CLK, WR, and RD inputs and forces the  
interface into a high-impedance (high-Z) state.  
External Reference  
With both the MAX1295 and MAX1297, an external refer-  
ence can be placed at either the input (REFADJ) or the  
output (REF) of the internal reference buffer amplifier.  
Input Format  
The control bit sequence is latched into the device on  
pins D7–D0 during a write command. Table 4 shows  
the control-byte format.  
Using the REFADJ input makes buffering the external  
reference unnecessary. The REFADJ input impedance  
is typically 17k.  
When applying an external reference to REF, disable  
the internal reference buffer by connecting REFADJ to  
DD  
Therefore, an external reference at REF must deliver up  
to 200µA DC load current during a conversion and  
have an output impedance less than 10. If the refer-  
ence has higher output impedance or is noisy, bypass  
it close to the REF pin with a 4.7µF capacitor.  
Output Data Format  
The 12-bit-wide output format for both the MAX1295/  
MAX1297 is binary in unipolar mode and two’s comple-  
ment in bipolar mode. CS, RD, WR, INT, and the 12 bits  
of output data can interface directly to a 16-bit data bus.  
When reading the output data, CS and RD must be low.  
V
. The DC input resistance at REF is 25k.  
__________Applications Information  
Power-Down Modes  
To save power, place the converter in a low-current  
shutdown state between conversions. Select standby  
mode or shutdown mode using bits D6 and D7 of the  
control byte (Tables 1 and 4). In both software power-  
down modes, the parallel interface remains active, but  
the ADC does not convert.  
Power-On Reset  
When power is first applied, internal power-on reset cir-  
cuitry activates the MAX1295/MAX1297 in external clock  
mode and sets INT high. After the power supplies stabi-  
lize, the internal reset time is 10µs; no conversions  
should be attempted during this phase. When using the  
internal reference, 500µs is required for V  
to stabilize.  
REF  
Standby Mode  
While in standby mode, the supply current is typically  
850µA. The part powers up on the next rising edge of  
WR and is ready to perform conversions. This quick  
turn-on time allows the user to realize significantly  
reduced power consumption for conversion rates  
below 265ksps.  
Internal and External Reference  
The MAX1295/MAX1297 can be used with an internal  
or external reference voltage. An external reference  
can be connected directly to REF or REFADJ.  
14 ______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Tꢁble .0 Full-Lcꢁle ꢁnd Zeao-Lcꢁle foa Unipolꢁa ꢁnd Bipolꢁa Opeaꢁtion  
UNIPOꢀAR MODE  
BIPOꢀAR MODE  
Zero Scale  
Full Scale  
COM  
+ COM  
Zero Scale  
COM  
Positive Full Scale  
Negative Full Scale  
V
/2 + COM  
REF  
V
REF  
-V  
/2 + COM  
REF  
OUTPUT CODE  
REF  
OUTPUT CODE  
FULL-SCALE  
TRANSITION  
FS  
=
+ COM  
+ COM  
FS = REF + COM  
ZS = COM  
011 . . . 111  
111 . . . 111  
2
011 . . . 110  
111 . . . 110  
ZS = COM  
-REF  
2
-FS =  
000 . . . 010  
000 . . . 001  
000 . . . 000  
100 . . . 010  
100 . . . 001  
100 . . . 000  
REF  
4096  
REF  
4096  
1 LSB =  
1 LSB =  
111 . . . 111  
111 . . . 110  
111 . . . 101  
011 . . . 111  
011 . . . 110  
011 . . . 101  
100 . . . 001  
100 . . . 000  
000 . . . 001  
000 . . . 000  
COM*  
INPUT VOLTAGE (LSB)  
- FS  
+FS - 1 LSB  
0
1
2
FS  
2048  
INPUT VOLTAGE (LSB)  
(COM)  
FS - 3/2 LSB  
*COM V /2  
REF  
Figure 8. Unipolar Transfer Function  
Figure 9. Bipolar Transfer Function  
Shutdown Mode  
Transfer Function  
Shutdown mode turns off all chip functions that draw qui-  
escent current, reducing the typical supply current to  
2µA immediately after the current conversion is complet-  
ed. A rising edge on WR causes the MAX1295/MAX1297  
to exit shutdown mode and return to normal operation.  
To achieve full 12-bit accuracy with a 4.7µF reference  
bypass capacitor, 50µs is required after power-up.  
Waiting 50µs in standby mode, instead of in full-power  
mode, can reduce power consumption by a factor of 3 or  
more. When using an external reference, only 50µs is  
required after power-up. Enter standby mode by per-  
forming a dummy conversion with the control byte speci-  
fying standby mode.  
Table 5 shows the full-scale voltage ranges for unipolar  
and bipolar modes. Figure 8 depicts the nominal unipo-  
lar input/output (I/O) transfer function, and Figure 9  
shows the bipolar I/O transfer function. Code transitions  
occur halfway between successive-integer LSB values.  
Output coding is binary, with 1 LSB = (V  
/ 4096).  
REF  
Maximum Sampling Rate/  
Achieving 300ksps  
When running at the maximum clock frequency of  
4.8MHz, the specified throughput of 265ksps is achieved  
by completing a conversion every 18 clock cycles: 1  
write cycle, 3 acquisition cycles, 13 conversion cycles,  
and 1 read cycle. This assumes that the results of the  
last conversion are read before the next control byte is  
written. It is possible to achieve higher throughputs, up  
to 300ksps, by first writing a control byte to begin the  
Note: Bypass capacitors larger than 4.7µF between  
REF and GND result in longer power-up delays.  
______________________________________________________________________________________ 1.  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
1
2
3
4
5
6
7
8
9
10  
11  
12  
13  
14  
15  
16  
CLK  
WR  
RD  
D11–D0  
CONTROL  
WORD  
D11–  
D0  
CONTROL WORD  
CONVERSION  
D7–D0  
STATE  
ACQUISITION  
ACQUISITION  
SAMPLING INSTANT  
Figure 10. Timing Diagram for Fastest Conversion  
ing of the data bus during acquisition or conversion can  
cause additional supply noise, which can make it diffi-  
cult to achieve true 12-bit performance.  
SUPPLIES  
Layout, Grounding, and Bypassing  
For best performance, use printed circuit (PC) boards.  
Wire-wrap configurations are not recommended since  
the layout should ensure proper separation of analog  
and digital traces. Do not run analog and digital lines  
parallel to each other, and don’t lay out digital signal  
paths underneath the ADC package. Use separate  
analog and digital PC board ground sections with only  
one star point (Figure 11) connecting the two ground  
systems (analog and digital). For lowest noise opera-  
tion, ensure the ground return to the star ground’s  
power supply is low impedance and as short as possi-  
ble. Route digital signals far away from sensitive analog  
and reference inputs.  
+3V  
+3V  
GND  
4.7µF  
0.1µF  
*R = 5Ω  
V
DD  
GND  
COM  
+3V  
DGND  
DIGITAL  
CIRCUITRY  
MAX1295  
MAX1297  
*OPTIONAL  
High-frequency noise in the power supply, V , could  
DD  
impair operation of the ADC’s fast comparator. Bypass  
Figure 11. Power-Supply and Grounding Connections  
V
to the star ground with a network of two parallel  
DD  
capacitors, 0.1µF and 4.7µF, located as close as to the  
MAX1295/MAX1297’s power-supply pin as possible.  
Minimize capacitor lead length for best supply-noise  
rejection and add an attenuation resistor (5) if the  
power supply is extremely noisy.  
acquisition cycle of the next conversion, and then read-  
ing the results of the previous conversion from the bus.  
This technique (Figure 10) allows a conversion to be  
completed every 16 clock cycles. Note that the switch-  
16 ______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Signal-to-Noise Plus Distortion  
Signal-to-noise plus distortion (SINAD) is the ratio of the  
Definitions  
Integral Nonlinearity  
Integral nonlinearity (INL) 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. INL for  
the MAX1295/MAX1297 is measured using the end-  
point method.  
fundamental input frequency’s RMS amplitude to the  
RMS equivalent of all other ADC output signals:  
SINAD (dB) = 20 × log (Signal  
/ Noise  
)
RMS  
RMS  
Effective Number of Bits  
Effective number of bits (ENOB) indicates the global  
accuracy of an ADC at a specific input frequency and  
sampling rate. An ideal ADC’s error consists of quanti-  
zation noise only. With an input range equal to the full-  
scale range of the ADC, calculate the effective number  
of bits as follows:  
Differential Nonlinearity  
Differential nonlinearity (DNL) is the difference between  
an actual step width and the ideal value of 1 LSB. A  
DNL error specification of less than 1 LSB guarantees  
no missing codes and a monotonic transfer function.  
ENOB = (SINAD - 1.76) / 6.02  
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:  
Aperture Jitter  
Aperture jitter (t ) is the sample-to-sample variation in  
AJ  
the time between the samples.  
Aperture Delay  
Aperture delay (t ) is the time between the rising  
AD  
edge of the sampling clock and the instant when an  
actual sample is taken.  
2
2
2
2
THD = 20 × log  
V
+ V + V + V  
/ V  
1
2
3
4
5
Signal-to-Noise Ratio  
For a waveform perfectly reconstructed from digital  
samples, signal-to-noise ratio (SNR) is the ratio of the  
full-scale analog input (RMS value) to the RMS quanti-  
zation error (residual error). The ideal, theoretical mini-  
mum analog-to-digital noise is caused by quantization  
error only and results directly from the ADC’s resolution,  
(N Bits):  
where V1 is the fundamental amplitude, and V2 through  
V5 are the amplitudes of the 2nd- through 5th-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.  
SNR = (6.02 × N + 1.76)dB  
In reality, there are other noise sources besides quanti-  
zation noise, including thermal noise, reference noise,  
clock jitter, etc. Therefore, SNR is calculated by taking  
the ratio of the RMS signal to the RMS noise, which  
includes all spectral components minus the fundamen-  
tal, the first five harmonics, and the DC offset.  
Chip Information  
TRANSISTOR COUNT: 5781  
SUBSTRATE CONNECTED TO GND  
______________________________________________________________________________________ 17  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Typical Operating Circuits  
CLK  
CLK  
+3V  
+3V  
MAX1297  
V
MAX1295  
V
DD  
DD  
+2.5V  
+2.5V  
CS  
WR  
RD  
REF  
CS  
WR  
RD  
REF  
µP  
CONTROL  
INPUTS  
µP  
CONTROL  
INPUTS  
0.1µF  
0.1µF  
REFADJ  
REFADJ  
INT  
4.7µF  
4.7µF  
INT  
OUTPUT STATUS  
OUTPUT STATUS  
D11  
D10  
D9  
D11  
D10  
D9  
D8  
D8  
D7  
D6  
D7  
D6  
CH5  
CH4  
D5  
D4  
D3  
D5  
D4  
D3  
CH3  
CH2  
CH1  
ANALOG  
INPUTS  
CH1  
D2  
D2  
ANALOG  
INPUTS  
CH0  
CH0  
D1  
D0  
D1  
D0  
COM  
COM  
GND  
GND  
µP DATA BUS  
µP DATA BUS  
Pin Configurations (continued)  
TOP VIEW  
D9  
D8  
D7  
D6  
D5  
D4  
D3  
D2  
D1  
1
2
3
4
5
6
7
8
9
24 D10  
23 D11  
22  
V
DD  
21 REF  
20 REFADJ  
19 GND  
18 COM  
17 CH0  
16 CH1  
15 CS  
MAX1297  
D0 10  
INT 11  
RD 12  
14 CLK  
13 WR  
QLOP  
18 ______________________________________________________________________________________  
265ksps, +3V, 6-/2-Channel, 12-Bit ADCs  
with +2.5V Reference and Parallel Interface  
Package Information  
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,  
go to www0mꢁxim-ic0com/pꢁckꢁges.)  
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are  
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.  
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________19  
© 2002 Maxim Integrated Products  
Printed USA  
is a registered trademark of Maxim Integrated Products.  

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