Maxim MAX1227BEEE-T 12-bit 300ksps adcs with fifo, temp sensor, internal reference Datasheet

19-2851; Rev 1; 7/03
KIT
ATION
EVALU
E
L
B
A
AVAIL
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
The MAX1231 is available in 28-pin 5mm x 5mm QFN
with exposed pad and 24-pin QSOP packages. The
MAX1227/MAX1229 are only available in QSOP packages. All three devices are specified over the extended
-40°C to +85°C temperature range.
________________________Applications
Features
♦ Internal Temperature Sensor (±1°C Accuracy)
♦ 16-Entry First-In/First-Out (FIFO)
♦ Analog Multiplexer with True Differential
Track/Hold
16-, 12-, 8-Channel Single Ended
8-, 6-, 4-Channel True Differential
(Unipolar or Bipolar)
♦ Accuracy: ±1 LSB INL, ±1 LSB DNL, No Missing
Codes Over Temperature
♦ Scan Mode, Internal Averaging, and Internal Clock
♦ Low-Power Single +3V Operation
0.62mA at 300ksps
♦ Internal 2.5V Reference or External Differential
Reference
♦ 10MHz 3-Wire SPI/QSPI/MICROWIRE-Compatible
Interface
♦ Space-Saving 28-Pin 5mm x 5mm QFN Package
System Supervision
Ordering Information
Data-Acquisition Systems
Industrial Control Systems
PART
TEMP RANGE
PIN-PACKAGE
Patient Monitoring
MAX1227ACEE-T*
0°C to +70°C
16 QSOP
Data Logging
MAX1227AEEE-T*
-40°C to +85°C
16 QSOP
*Future product—contact factory for availability.
Instrumentation
AutoShutdown is a trademark of Maxim Integrated Products, Inc.
SPI/QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corp.
Ordering Information continued at end of data sheet.
Pin Configurations
TOP VIEW
AIN0 1
16 EOC
AIN1 2
15 DOUT
AIN2 3
14 DIN
AIN0 1
20 EOC
AIN1 2
19 DOUT
AIN2 3
18 DIN
17 CS
AIN3 4
AIN3 4
MAX1227
AIN4 5
MAX1229
16 SCLK
13 CS
AIN4 5
12 SCLK
AIN5 6
11 VDD
AIN5 6
15 VDD
AIN6 7
14 GND
AIN7 8
13 REF+
AIN8 9
12 CNVST/AIN11
AIN9 10
11 REF-/AIN10
10 GND
REF-/AIN6 7
CNVST/AIN7 8
9
REF+
QSOP
Pin Configurations continued at end of data sheet.
QSOP
________________________________________________________________ Maxim Integrated Products
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.
1
MAX1227/MAX1229/MAX1231
General Description
The MAX1227/MAX1229/MAX1231 are serial 12-bit analog-to-digital converters (ADCs) with an internal reference
and an internal temperature sensor. These devices feature on-chip FIFO, scan mode, internal clock mode, internal averaging, and AutoShutdown™. The maximum
sampling rate is 300ksps using an external clock. The
MAX1231 has 16 input channels, the MAX1229 has 12
input channels, and the MAX1227 has 8 input channels.
All input channels are configurable for single-ended or
differential inputs in unipolar or bipolar mode. All three
devices operate from a +3V supply and contain a 10MHz
SPI™/QSPI™/MICROWIRE™-compatible serial port.
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V
CS, SCLK, DIN, EOC, DOUT to GND.........-0.3V to (VDD + 0.3V)
AIN0–AIN13, REF-/AIN_, CNVST/AIN_,
REF+ to GND.........................................-0.3V to (VDD + 0.3V)
Maximum Current into Any Pin............................................50mA
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW
24-Pin QSOP (derate 9.5mW/°C above +70°C)...........762mW
28-Pin QFN 5mm x 5mm
(derate 20.8mW/°C above +70°C) ........................1667mW
Operating Temperature Ranges
MAX12__C__.......................................................0°C to +70°C
MAX12__E__ ....................................................-40°C to +85°C
Storage Temperature Range .............................-60°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
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
(VDD = +2.7V to +3.6V, fSAMPLE = 300kHz, fSCLK = 4.8MHz (50% duty cycle), VREF = 2.5V, TA = TMIN to TMAX, unless otherwise
noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
±1.0
LSB
±1.0
LSB
DC ACCURACY (NOTE 1)
Resolution
RES
Integral Nonlinearity
INL
Differential Nonlinearity
DNL
12
No missing codes over temperature
Offset Error
Gain Error
Bits
(Note 2)
Offset Error Temperature
Coefficient
±0.5
±4.0
LSB
±0.5
±4.0
LSB
±2
ppm/°C
FSR
Gain Temperature Coefficient
±0.8
ppm/°C
Channel-to-Channel Offset
Matching
±0.1
LSB
70
dB
-82
dBc
DYNAMIC SPECIFICATIONS (10kHz sine wave input, 2.5VP-P, 300ksps, fSCLK = 4.8MHz)
Signal-to-Noise Plus Distortion
SINAD
Total Harmonic Distortion
THD
Spurious-Free Dynamic Range
SFDR
Up to the 5th harmonic
80
dBc
fin1 = 9.9kHz, fin2 = 10.2kHz
76
dBc
Full-Power Bandwidth
-3dB point
1
MHz
Full-Linear Bandwidth
S / (N + D) > 68dB
25
kHz
Intermodulation Distortion
2
IMD
_______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
(VDD = +2.7V to +3.6V, fSAMPLE = 300kHz, fSCLK = 4.8MHz (50% duty cycle), VREF = 2.5V, TA = TMIN to TMAX, unless otherwise
noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CONVERSION RATE
Power-Up Time
tPU
Acquisition Time
tACQ
Conversion Time
tCONV
External Clock Frequency
fSCLK
External reference
0.8
Internal reference (Note 3)
65
Internally clocked
3.5
µs
0.6
Externally clocked (Note 4)
2.7
Externally clocked conversion
0.1
µs
4.8
Data I/O
SCLK Duty Cycle
µs
10
40
60
MHz
%
Aperture Delay
30
ns
Aperture Jitter
<50
ps
ANALOG INPUT
Unipolar
Input Voltage Range
Bipolar (Note 5)
Input Leakage Current
VIN = VDD
Input Capacitance
During acquisition time (Note 6)
0
VREF
-VREF / 2
VREF / 2
±0.01
±1
24
V
µA
pF
INTERNAL TEMPERATURE SENSOR
Grade A, TA = +25°C
Measurement Error (Note 7)
±0.3
Grade A, TA = -20°C to +85°C
±0.5
±1
Grade A, TA = TMIN to TMAX
±0.75
±1.5
Grade B, TA = +25°C
±0.7
Grade B, TA = TMIN to TMAX
±1.2
°C
±2.5
Temperature Measurement Noise
0.4
°CRMS
Temperature Resolution
1/8
°C
Power-Supply Rejection
0.3
°C/V
INTERNAL REFERENCE
REF Output Voltage
2.48
REF Temperature Coefficient
TCREF
2.50
Grade A
±8
Grade B
±30
2.52
V
ppm/°C
Output Resistance
6.5
kΩ
REF Output Noise
200
µVRMS
-70
dB
REF Power-Supply Rejection
PSRR
EXTERNAL REFERENCE INPUT
REF- Input Voltage Range
VREF-
REF+ Input Voltage Range
VREF+
REF+ Input Current
IREF+
0
500
1.0
VREF+ = 2.5V, fSAMPLE = 300ksps
VREF+ = 2.5V, fSAMPLE = 0
VDD + 50mV
40
100
±0.1
±5
mV
V
µA
_______________________________________________________________________________________
3
MAX1227/MAX1229/MAX1231
ELECTRICAL CHARACTERISTICS (continued)
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +2.7V to +3.6V, fSAMPLE = 300kHz, fSCLK = 4.8MHz (50% duty cycle), VREF = 2.5V, TA = TMIN to TMAX, unless otherwise
noted. Typical values are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS (SCLK, DIN, CS, CNVST)
Input Voltage Low
Input Voltage High
Input Hysteresis
VIL
VDD x 0.3
VIH
VDD x 0.7
VHYST
Input Leakage Current
IIN
Input Capacitance
CIN
V
V
200
VIN = 0 or VDD
±0.01
mV
±1.0
µA
15
pF
DIGITAL OUTPUTS (DOUT, EOC)
Output Voltage Low
VOL
Output Voltage High
VOH
Tri-State Leakage Current
Tri-State Output Capacitance
ISINK = 2mA
0.4
ISINK = 4mA
0.8
ISOURCE = 1.5mA
V
VDD - 0.5
V
IL
CS = VDD
±0.05
COUT
CS = VDD
15
±1
µA
pF
POWER REQUIREMENTS
Supply Voltage
VDD
2.7
Internal
reference
Supply Current (Note 8)
IDD
Power-Supply Rejection
PSR
2200
2700
fSAMPLE = 300ksps
1550
1800
fSAMPLE = 0, REF on
1000
1200
0.2
5
During temp sense
1550
2000
fSAMPLE = 300ksps
880
1100
Shutdown
0.2
5
±0.2
±1
Shutdown
External
reference
3.6
During temp sense
VDD = 2.7V to 3.6V; full-scale input
V
µA
mV
Tested at VDD = +2.7V, unipolar input mode.
Offset nulled.
Time for reference to power up and settle to within 1 LSB.
Conversion time is defined as the number of clock cycles multiplied by the clock period; clock has 50% duty cycle.
The operational input voltage range for each individual input of a differentially configured pair is from GND to VDD. The
operational input voltage difference is from -VREF / 2 to +VREF / 2.
Note 6: See Figure 3 (Input Equivalent Circuit) and the Sampling Error vs. Source Impedance curve in the Typical Operating
Characteristics section.
Note 7: Fast automated test, excludes self-heating effects.
Note 8: Supply current is specified depending on whether an internal or external reference is used for voltage conversions.
Temperature measurements always use the internal reference.
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
4
_______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
PARAMETER
SYMBOL
SCLK Clock Period
tCP
CONDITIONS
MIN
Externally clocked conversion
208
Data I/O
100
TYP
MAX
UNITS
ns
SCLK Duty Cycle
tCH
60
%
SCLK Fall to DOUT Transition
tDOT
CLOAD = 30pF
40
ns
CS Rise to DOUT Disable
tDOD
CLOAD = 30pF
40
ns
CS Fall to DOUT Enable
tDOE
CLOAD = 30pF
DIN to SCLK Rise Setup
tDS
SCLK Rise to DIN Hold
tDH
CS to SCLK Rise Setup
tCSS
SCLK Rise to CS Hold
tCSH
40
ns
40
tTS
CS or CNVST Rise to EOC
Low (Note 9)
ns
ns
0
tCSW
CNVST Pulse Width
40
40
ns
0
ns
CKSEL = 00, CKSEL = 01 (temp sense)
40
ns
CKSEL = 01 (voltage conversion)
1.4
µs
Temp sense
55
Voltage conversion
7
Reference power-up
65
µs
Note 9: This time is defined as the number of clock cycles needed for conversion multiplied by the clock period. If the internal reference needs to be powered up, the total time is additive. The internal reference is always used for temperature measurements.
Typical Operating Characteristics
(VDD = +3V, VREF = +2.5V, fSCLK = 4.8MHz, CLOAD = 30pF, TA = +25°C, unless otherwise noted.)
0.4
0.2
0
-0.2
-0.4
-0.6
0.8
0.6
0.4
90
80
AMPLITUDE (dB)
0.6
SINAD vs. FREQUENCY
100
MAX1227/29/31 toc02
INTEGRAL NONLINEARITY (LSB)
0.8
1.0
DIFFERENTIAL NONLINEARITY (LSB)
MAX1227/29/31 toc01
1.0
DIFFERENTIAL NONLINEARITY
vs. OUTPUT CODE
0.2
0
-0.2
70
60
50
40
-0.4
30
-0.6
20
-0.8
-0.8
10
-1.0
-1.0
0
1024
2048
OUTPUT CODE
3072
4096
MAX1227/29/31 toc03
INTEGRAL NONLINEARITY
vs. OUTPUT CODE
0
0
1024
2048
OUTPUT CODE
3072
4096
0.1
1
10
100
1000
FREQUENCY (kHz)
_______________________________________________________________________________________
5
MAX1227/MAX1229/MAX1231
TIMING CHARACTERISTICS (Figure 1)
Typical Operating Characteristics (continued)
(VDD = +3V, VREF = +2.5V, fSCLK = 4.8MHz, CLOAD = 30pF, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. SAMPLING RATE
60
40
MAX1227/29/31 toc05
500
400
0
200
10
100
1000
500
1
FREQUENCY (kHz)
10
100
1000
SUPPLY CURRENT vs. TEMPERATURE
625
MAX1227/29/31 toc07
0.4
fS = 300ksps
SUPPLY CURRENT (µA)
SHUTDOWN SUPPLY CURRENT (µA)
0.5
3.3
SUPPLY VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
0.3
0.2
620
615
610
0.1
0
605
2.7
3.0
3.3
3.6
-40
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
INTERNAL REFERENCE VOLTAGE
vs. SUPPLY VOLTAGE
0.4
0.3
0.2
0.1
2.4990
INTERNAL REFERENCE VOLTAGE (V)
MAX1227/29/31 toc09
0.5
SHUTDOWN SUPPLY CURRENT (µA)
3.0
2.7
SAMPLING RATE (ksps)
MAX1227/29/31 toc08
1
600
85
MAX1227/29/31 toc10
0.1
650
550
300
20
2.4986
2.4982
2.4978
2.4974
2.4970
0
-40
-15
10
35
TEMPERATURE (°C)
6
SUPPLY CURRENT vs. SUPPLY VOLTAGE
700
SUPPLY CURRENT (µA)
80
600
SUPPLY CURRENT (µA)
MAX1227/29/31 toc04
100
700
MAX1227/29/31 toc06
SFDR vs. FREQUENCY
120
AMPLITUDE (dB)
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
60
85
2.7
3.0
3.3
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3.6
3.6
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
2.502
2.498
2.494
0.3
OFFSET ERROR (LSB)
0.2
OFFSET ERROR (LSB)
2.506
0.4
MAX1227/29/31 toc12
0.3
MAX1227/29/31 toc11
2.510
0.1
0
-0.1
-0.2
2.490
-15
10
35
60
TEMPERATURE (°C)
3.0
3.3
-0.1
-40
3.6
-15
35
60
85
GAIN ERROR vs. TEMPERATURE
1.5
GAIN ERROR (LSB)
1.0
MAX1227/29/31 toc15
2.0
MAX1227/29/31 toc14
1.5
10
TEMPERATURE (°C)
GAIN ERROR vs. SUPPLY VOLTAGE
1.0
0.5
0.5
0
2.7
3.0
-40
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE SENSOR ERROR
vs. TEMPERATURE
SAMPLING ERROR
vs. SOURCE IMPEDANCE
0.75
0.50
GRADE A
0.25
0
-0.25
GRADE B
1
0
SAMPLING ERROR (LSB)
MAX1227/29/31 toc16
1.00
-0.50
0
3.6
3.3
85
MAX1227/29/31 toc17
GAIN ERROR (LSB)
0
SUPPLY VOLTAGE (V)
2.0
-1
-2
-3
-4
-0.75
-1.00
0.1
-0.3
2.7
85
0.2
-0.2
-0.3
-40
TEMPERATURE SENSOR ERROR (°C)
INTERNAL REFERENCE VOLTAGE (V)
OFFSET ERROR
vs. TEMPERATURE
OFFSET ERROR
vs. SUPPLY VOLTAGE
MAX1227/29/31 toc13
INTERNAL REFERENCE VOLTAGE
vs. TEMPERATURE
-5
-40
-15
10
35
TEMPERATURE (°C)
60
85
0
2
4
6
8
10
SOURCE IMPEDANCE (kΩ)
_______________________________________________________________________________________
7
MAX1227/MAX1229/MAX1231
Typical Operating Characteristics (continued)
(VDD = +3V, VREF = +2.5V, fSCLK = 4.8MHz, CLOAD = 30pF, TA = +25°C, unless otherwise noted.)
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
MAX1227/MAX1229/MAX1231
Pin Description
8
MAX1231
QFN
MAX1231
QSOP
MAX1229
MAX1227
NAME
2–12, 26,
27, 28,
1–14
—
—
AIN0–13
—
—
1–10
—
AIN0–9
Analog Inputs
—
—
—
1–6
AIN0–5
Analog Inputs
13
15
—
—
REF-/AIN14
Negative Input for External Differential Reference/Analog Input 14.
See Table 3 for details on programming the setup register.
—
—
11
—
REF-/AIN10
Negative Input for External Differential Reference/Analog Input 10.
See Table 3 for details on programming the setup register.
—
—
—
7
REF-/AIN6
Negative Input for External Differential Reference/Analog Input 6.
See Table 3 for details on programming the setup register.
14
16
—
—
CNVST/
AIN15
Active-Low Conversion Start Input/Analog Input 15. See Table 3
for details on programming the setup register.
—
—
12
—
CNVST/
AIN11
Active-Low Conversion Start Input/Analog Input 11. See Table 3
for details on programming the setup register.
—
—
—
8
CNVST/
AIN7
Active-Low Conversion Start Input/Analog Input 7. See Table 3 for
details on programming the setup register.
15
17
13
9
REF+
Positive Reference Input. Bypass to GND with a 0.1µF capacitor.
16
18
14
10
GND
Ground
18
19
15
11
VDD
Power Input. Bypass to GND with a 0.1µF capacitor.
20
20
16
12
SCLK
21
21
17
13
CS
Active-Low Chip Select Input. When CS is low, the serial interface
is enabled. When CS is high, DOUT is high impedance.
22
22
18
14
DIN
Serial Data Input. DIN data is latched into the serial interface on
the rising edge of SCLK.
23
23
19
15
DOUT
Serial Data Output. Data is clocked out on the falling edge of
SCLK. High impedance when CS is connected to VDD.
24
1, 17, 19,
25
24
20
16
EOC
End of Conversion Output. Data is valid after EOC pulls low.
—
—
—
N.C.
No Connection. Not internally connected.
FUNCTION
Analog Inputs
Serial Clock Input. Clocks data in and out of the serial interface.
(Duty cycle must be 40% to 60%.) See Table 3 for details on
programming the clock mode.
_______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
MAX1227/MAX1229/MAX1231
CS
tCP
tCH
tCSS
tCSH
tCSH
tCSS
SCLK
tDH
tDS
DIN
tDOT
tDOD
tDOE
DOUT
Figure 1. Detailed Serial-Interface Timing Diagram
CS
DIN
SCLK
SERIAL
INTERFACE
OSCILLATOR
CONTROL
DOUT
EOC
CNVST
AIN1
AIN2
T/H
AIN15
12-BIT
SAR
ADC
FIFO AND
ACCUMULATOR
TEMP
SENSE
REFREF+
INTERNAL
REFERENCE
MAX1227
MAX1229
MAX1231
Figure 2. Functional Diagram
Detailed Description
The MAX1227/MAX1229/MAX1231 are low-power, serial-output, multichannel ADCs with temperature-sensing
capability for temperature-control, process-control, and
monitoring applications. These 12-bit ADCs have internal track and hold (T/H) circuitry that supports singleended and fully differential inputs. Data is converted
from an internal temperature sensor or analog voltage
sources in a variety of channel and data-acquisition
configurations. Microprocessor (µP) control is made
easy through a 3-wire SPI/QSPI/MICROWIRE-compatible
serial interface.
Figure 2 shows a simplified functional diagram of the
MAX1227/MAX1229/MAX1231 internal architecture.
The MAX1227 has eight single-ended analog input
channels or four differential channels. The MAX1229
has 12 single-ended analog input channels or six differential channels. The MAX1231 has 16 single-ended
analog input channels or eight differential channels.
_______________________________________________________________________________________
9
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Converter Operation
The MAX1227/MAX1229/MAX1231 ADCs use a fully differential, successive-approximation register (SAR) conversion technique and an on-chip T/H block to convert
temperature and voltage signals into a 12-bit digital
result. Both single-ended and differential configurations
are supported, with a unipolar signal range for singleended mode and bipolar or unipolar ranges for differential mode.
Input Bandwidth
The ADC’s input-tracking circuitry has a 1MHz smallsignal bandwidth, so it is possible to digitize highspeed transient events and measure periodic signals
with bandwidths exceeding the ADC’s sampling rate by
using undersampling techniques. Anti-alias prefiltering
of the input signals is necessary to avoid high-frequency signals aliasing into the frequency band of interest.
Analog Input Protection
Internal ESD protection diodes clamp all pins to VDD
and GND, allowing the inputs to swing from (GND 0.3V) to (VDD + 0.3V) without damage. However, for
accurate conversions near full scale, the inputs must
not exceed VDD by more than 50mV or be lower than
GND by 50mV. If an off-channel analog input voltage
exceeds the supplies, limit the input current to 2mA.
Tables 1–7 detail the register descriptions. Bits 5 and 4,
CKSEL1 and CKSEL0, respectively, control the clock
modes in the setup register (see Table 3). Choose
between four different clock modes for various ways to
start a conversion and determine whether the acquisitions are internally or externally timed. Select clock
mode 00 to configure CNVST/AIN_ to act as a conversion start and use it to request the programmed, internally timed conversions without tying up the serial bus.
In clock mode 01, use CNVST to request conversions
one channel at a time, controlling the sampling speed
without tying up the serial bus. Request and start internally timed conversions through the serial interface by
writing to the conversion register in the default clock
mode 10. Use clock mode 11 with SCLK up to 4.8MHz
for externally timed acquisitions to achieve sampling
rates up to 300ksps. Clock mode 11 disables scanning
and averaging. See Figures 4–7 for timing specifications and how to begin a conversion.
These devices feature an active-low, end-of-conversion
output. EOC goes low when the ADC completes the lastrequested operation and is waiting for the next input
data byte (for clock modes 00 and 10). In clock mode
01, EOC goes low after the ADC completes each
requested operation. EOC goes high when CS or CNVST
goes low. EOC is always high in clock mode 11.
3-Wire Serial Interface
Single-Ended/Differential Input
The MAX1227/MAX1229/MAX1231 feature a serial
interface compatible with SPI/QSPI and MICROWIRE
devices. For SPI/QSPI, ensure the CPU serial interface
runs in master mode so it generates the serial clock
signal. Select the SCLK frequency of 10MHz or less,
and set clock polarity (CPOL) and phase (CPHA) in the
µP control registers to the same value. The MAX1227/
MAX1229/MAX1231 operate with SCLK idling high or
low, and thus operate with CPOL = CPHA = 0 or CPOL
= CPHA = 1. Set CS low to latch input data at DIN on
the rising edge of SCLK. Output data at DOUT is
updated on the falling edge of SCLK. Bipolar true differential results and temperature sensor results are
available in two’s complement format, while all others
are in binary.
Serial communication always begins with an 8-bit input
data byte (MSB first) loaded from DIN. Use a second
byte, immediately following the setup byte, to write to
the unipolar mode or bipolar mode registers (see
Tables 1, 3, 4, and 5). A high-to-low transition on CS initiates the data input operation. The input data byte and
the subsequent data bytes are clocked from DIN into
the serial interface on the rising edge of SCLK.
The MAX1227/MAX1229/MAX1231 use a fully differential ADC for all conversions. The analog inputs can be
configured for either differential or single-ended conversions by writing to the setup register (see Table 3).
Single-ended conversions are internally referenced to
GND (see Figure 3).
In differential mode, the T/H samples the difference
between two analog inputs, eliminating common-mode
DC offsets and noise. IN+ and IN- are selected from
the following pairs: AIN0/AIN1, AIN2/AIN3, AIN4/AIN5,
AIN6/AIN7, AIN8/AIN9, AIN10/AIN11, AIN12/AIN13,
and AIN14/AIN15. AIN0–AIN7 are available on the
MAX1227, MAX1229, and MAX1231. AIN8–AIN11 are
only available on the MAX1229 and MAX1231.
AIN12–AIN15 are only available on the MAX1231. See
Tables 2–5 for more details on configuring the inputs.
For the inputs that can be configured as CNVST or an
analog input, only one can be used at a time. For the
inputs that can be configured as REF- or an analog
input, the REF- configuration excludes the analog input.
10
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
CIN+
DAC
COMPARATOR
+
HOLD
GND
(SINGLE ENDED);
AIN1, AIN3,
AIN5…AIN15
(DIFFERENTIAL)
CIN-
HOLD
HOLD
VDD/2
Figure 3. Equivalent Input Circuit
Unipolar/Bipolar
Address the unipolar and bipolar registers through the
setup register (bits 1 and 0). Program a pair of analog
channels for differential operation by writing a 1 to the
appropriate bit of the bipolar or unipolar register.
Unipolar mode sets the differential input range from 0
to VREF. A negative differential analog input in unipolar
mode causes the digital output code to be zero.
Selecting bipolar mode sets the differential input range
to ±VREF / 2. The digital output code is binary in unipolar mode and two’s complement in bipolar mode
(Figures 8 and 9).
In single-ended mode, the MAX1227/MAX1229/
MAX1231 always operate in unipolar mode. The analog
inputs are internally referenced to GND with a full-scale
input range from 0 to VREF.
True Differential Analog Input T/H
The equivalent circuit of Figure 3 shows the MAX1227/
MAX1229/MAX1231s’ input architecture. In track mode,
a positive input capacitor is connected to AIN0–AIN15
in single-ended mode (and AIN0, AIN2, AIN4…AIN14
in differential mode). A negative input capacitor is connected to GND in single-ended mode (or AIN1, AIN3,
AIN5…AIN15 in differential mode). For external T/H
timing, use clock mode 01. After the T/H enters hold
mode, the difference between the sampled positive
and negative input voltages is converted. The time
required for the T/H to acquire an input signal is determined by how quickly its input capacitance is charged.
If the input signal’s source impedance is high, the
required acquisition time lengthens. The acquisition
t AQC = 9 x (RS + RIN ) x 24pF + tPWR
where RIN = 1.5kΩ, RS is the source impedance of the
input signal, and tPWR = 1µs, the power-up time of the
device. The varying power-up times are detailed in the
explanation of the clock mode conversions.
tACQ is never less than 1.4µs, and any source impedance below 300Ω does not significantly affect the
ADC’s AC performance. A high-impedance source can
be accommodated either by lengthening tACQ or by
placing a 1µF capacitor between the positive and negative analog inputs.
Internal FIFO
The MAX1227/MAX1229/MAX1231 contain a FIFO
buffer that can hold up to 16 ADC results plus one temperature result. This allows the ADC to handle multiple
internally clocked conversions and a temperature measurement, without tying up the serial bus.
If the FIFO is filled and further conversions are requested without reading from the FIFO, the oldest ADC
results are overwritten by the new ADC results. Each
result contains 2 bytes, with the MSB preceded by four
leading zeros. After each falling edge of CS, the oldest
available byte of data is available at DOUT, MSB first.
When the FIFO is empty, DOUT is zero.
The first 2 bytes of data read out after a temperature
measurement always contain the temperature result
preceded by four leading zeros, MSB first. If another
temperature measurement is performed before the first
temperature result is read out, the old measurement is
overwritten by the new result. Temperature results are
in degrees Celsius (two’s complement) at a resolution
of 1/8 of a degree. See the Temperature Measurements
section for details on converting the digital code to a
temperature.
Internal Clock
The MAX1227/MAX1229/MAX1231 operate from an
internal oscillator, which is accurate within 10% of the
4.4MHz nominal clock rate. The internal oscillator is
active in clock modes 00, 01, and 10. Read out the
data at clock speeds up to 10MHz. See Figures
4–7 for details on timing specifications and starting a
conversion.
______________________________________________________________________________________
11
MAX1227/MAX1229/MAX1231
REF
GND
AIN0-AIN15
(SINGLE ENDED);
AIN0, AIN2,
AIN4…AIN14
(DIFFERENTIAL)
time, tACQ, is the maximum time needed for a signal to
be acquired, plus the power-up time. It is calculated by
the following equation:
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Applications Information
Register Descriptions
The MAX1227/MAX1229/MAX1231 communicate
between the internal registers and the external circuitry
through the SPI/QSPI-compatible serial interface. Table
1 details the registers and the bit names. Tables 2–7
show the various functions within the conversion register, setup register, averaging register, reset register,
unipolar register, and bipolar register.
Conversion Time Calculations
The conversion time for each scan is based on a number of different factors: conversion time per sample,
samples per result, results per scan, if a temperature
measurement is requested, and if the external reference is in use.
Use the following formula to calculate the total conversion time for an internally timed conversion in clock
modes 00 and 10 (see the Electrical Characteristics
section as applicable):
total conversion time = tcnv x navg x nresult + tTS + tRP
where:
tcnv = tacq(max) + tconv(max)
navg = samples per result (amount of averaging)
nresult = number of FIFO results requested; determined
by number of channels being scanned or by NSCAN1,
NSCAN0
tTS = time required for temperature measurement; set
to zero if temp measurement is not requested
tRP = internal reference wake up; set to zero if internal
reference is already powered up or external reference
is being used
In clock mode 01, the total conversion time depends on
how long CNVST is held low or high, including any time
required to turn on the internal reference. Conversion
time in externally clocked mode (CKSEL1, CKSEL0 = 11)
depends on the SCLK period and how long CS is held
high between each set of eight SCLK cycles. In clock
mode 01, the total conversion time does not include the
time required to turn on the internal reference.
Conversion Register
Select active analog input channels, scan modes, and
a single temperature measurement per scan by writing
to the conversion register. Table 2 details channel
selection, the four scan modes, and how to request a
temperature measurement. Request a scan by writing
to the conversion register when in clock mode 10 or 11,
or by applying a low pulse to the CNVST pin when in
clock mode 00 or 01.
A conversion is not performed if it is requested on a
channel that has been configured as CNVST or REF-.
Do not request conversions on channels 8–15 on the
MAX1227 and channels 12–15 on the MAX1229. Set
CHSEL3:CHSEL0 to the lower channel’s binary values.
If the last two channels are configured as a differential
pair and one of them has been reconfigured as CNVST
or REF-, the pair is ignored.
Select scan mode 00 or 01 to return one result per single-ended channel and one result per differential pair
within the requested range, plus one temperature result if
selected. Select scan mode 10 to scan a single input
channel numerous times, depending on NSCAN1 and
NSCAN0 in the averaging register (Table 6). Select scan
mode 11 to return only one result from a single channel.
Setup Register
Write a byte to the setup register to configure the clock,
reference, and power-down modes. Table 3 details the
Table 1. Input Data Byte (MSB First)
REGISTER NAME
Conversion
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1
CHSEL3
CHSEL2
CHSEL1
CHSEL0
SCAN1
SCAN0
TEMP
Setup
0
1
CKSEL1
CKSEL0
REFSEL1
REFSEL0
DIFFSEL1
DIFFSEL0
Averaging
0
0
1
AVGON
NAVG1
NAVG0
NSCAN1
NSCAN0
Reset
0
0
0
1
RESET
X
X
X
Unipolar mode (setup)
UCH0/1
UCH2/3
UCH4/5
UCH6/7
UCH8/9*
Bipolar mode (setup)
BCH0/1
BCH1/2
BCH4/5
BCH6/7
BCH8/9*
UCH10/11 UCH12/138** UCH14/15**
BCH10/11 BCH12/13** BCH14/15**
*Unipolar/bipolar channels 8–15 are only valid on the MAX1229 and MAX1231.
**Unipolar/bipolar channels 12–15 are only valid on the MAX1231.
X = Don’t care.
12
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
BIT
NAME
—
BIT
FUNCTION
7 (MSB) Set to 1 to select conversion register.
CHSEL3
6
Analog input channel select.
CHSEL2
5
Analog input channel select.
CHSEL1
4
Analog input channel select.
CHSEL0
3
Analog input channel select.
SCAN1
2
Scan mode select.
SCAN0
1
Scan mode select.
TEMP
Set to 1 to take a single temperature
0 (LSB) measurement. The first conversion result
of a scan contains temperature information.
*See below for bit details.
CHSEL3
CHSEL2
CHSEL1
CHSEL0
SELECTED
CHANNEL (N)
0
0
0
0
AIN0
0
0
0
1
AIN1
0
0
1
0
AIN2
0
0
1
1
AIN3
0
1
0
0
AIN4
0
1
0
1
AIN5
0
1
1
0
AIN6
0
1
1
1
AIN7
1
0
0
0
AIN8
1
0
0
1
AIN9
1
0
1
0
AIN10
1
0
1
1
AIN11
1
1
0
0
AIN12
1
1
0
1
AIN13
1
1
1
0
AIN14
1
1
1
1
AIN15
SCAN1 SCAN0
SCAN MODE (CHANNEL N IS
SELECTED BY BITS CHSEL3–CHSEL0)
0
0
Scans channels 0 through N.
0
1
Scans channels N through the highest
numbered channel.
1
0
Scans channel N repeatedly. The averaging
register sets the number of results.
1
1
No scan. Converts channel N once only.
bits in the setup register. Bits 5 and 4 (CKSEL1 and
CKSEL0) control the clock mode, acquisition and sampling, and the conversion start. Bits 3 and 2 (REFSEL1
and REFSEL0) control internal or external reference use.
Bits 1 and 0 (DIFFSEL1 and DIFFSEL0) address the
unipolar mode and bipolar mode registers and configure
the analog input channels for differential operation.
Unipolar/Bipolar Registers
The final 2 bits (LSBs) of the setup register control the
unipolar/bipolar mode address registers. Set bits 1 and
0 (DIFFSEL1 and DIFFSEL0) to 10 to write to the unipolar mode register. Set bits 1 and 0 to 11 to write to the
bipolar mode register. In both cases, the setup byte
must be followed immediately by 1 byte of data written
to the unipolar register or bipolar register. Hold CS low
and run 16 SCLK cycles before pulling CS high. If the
last 2 bits of the setup register are 00 or 01, neither the
unipolar mode register nor the bipolar mode register is
written. Any subsequent byte is recognized as a new
input data byte. See Tables 4 and 5 to program the
unipolar and bipolar mode registers.
If a channel is configured as both unipolar and bipolar,
the unipolar setting takes precedence. In unipolar
mode, AIN+ can exceed AIN- by up to VREF. The output format in unipolar mode is binary. In bipolar mode,
either input can exceed the other by up to VREF / 2. The
output format in bipolar mode is two's complement.
Averaging Register
Write to the averaging register to configure the ADC to
average up to 32 samples for each requested result,
and to independently control the number of results
requested for single-channel scans.
Table 2 details the four scan modes available in the conversion register. All four scan modes allow averaging as
long as the AVGON bit, bit 4 in the averaging register, is
set to 1. Select scan mode 10 to scan the same channel
multiple times. Clock mode 11 disables averaging.
Reset Register
Write to the reset register (as shown in Table 7) to clear
the FIFO or to reset all registers to their default states.
Set the RESET bit to 1 to reset the FIFO. Set the reset
bit to zero to return the MAX1227/MAX1229/MAX1231
to the default power-up state.
Power-Up Default State
The MAX1227/MAX1229/MAX1231 power up with all
blocks in shutdown, including the reference. All registers
power up in state 00000000, except for the setup register, which powers up in clock mode 10 (CKSEL1 = 1).
______________________________________________________________________________________
13
MAX1227/MAX1229/MAX1231
Table 2. Conversion Register*
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Table 3. Setup Register*
BIT NAME
BIT
FUNCTION
—
7 (MSB)
—
6
Set to 1 to select setup register.
CKSEL1
5
Clock mode and CNVST configuration. Resets to 1 at power-up.
CKSEL0
4
Clock mode and CNVST configuration.
REFSEL1
3
Reference mode configuration.
REFSEL0
2
Reference mode configuration.
DIFFSEL1
1
Unipolar/bipolar mode register configuration for differential mode.
DIFFSEL0
0 (LSB)
Unipolar/bipolar mode register configuration for differential mode.
Set to zero to select setup register.
*See below for bit details.
CKSEL1
CKSEL0
CONVERSION CLOCK
ACQUISITION/SAMPLING
CNVST CONFIGURATION
0
0
Internal
Internally timed
CNVST
0
1
Internal
Externally timed through CNVST
CNVST
1
0
Internal
Internally timed
AIN15/11/7
1
1
External (4.8MHz max)
Externally timed through SCLK
AIN15/11/7
REFSEL1
REFSEL0
VOLTAGE REFERENCE
AutoShutdown
REF- CONFIGURATION
Reference off after scan; need
wake-up delay.
AIN14/10/6
0
0
Internal
0
1
External single ended
Reference off; no wake-up delay.
AIN14/10/6
AIN14/10/6
REF-
1
0
Internal
Reference always on; no wake-up
delay.
1
1
External differential
Reference off; no wake-up delay.
DIFFSEL1
DIFFSEL0
0
0
0
1
No data follows the setup byte. Unipolar mode and bipolar mode registers remain unchanged.
1
0
One byte of data follows the setup byte and is written to the unipolar mode register.
1
1
One byte of data follows the setup byte and is written to the bipolar mode register.
14
FUNCTION
No data follows the setup byte. Unipolar mode and bipolar mode registers remain unchanged.
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Output Data Format
Figures 4–7 illustrate the conversion timing for the
MAX1227/MAX1229/MAX1231. The 12-bit conversion
result is output in MSB-first format with four leading
zeros. DIN data is latched into the serial interface on
the rising edge of SCLK. Data on DOUT transitions on
the falling edge of SCLK. Conversions in clock modes 00
and 01 are initiated by CNVST. Conversions in clock
modes 10 and 11 are initiated by writing an input data
byte to the conversion register. Data is binary for unipolar mode and two’s complement for bipolar mode.
The reference voltage used for the temperature measurements is derived from the internal reference source
to ensure that 1 LSB corresponds to 1/8 of a degree.
Table 4. Unipolar Mode Register (Addressed Through Setup Register)
BIT NAME
BIT
FUNCTION
UCH0/1
7 (MSB)
Set to 1 to configure AIN0 and AIN1 for unipolar differential conversion.
UCH2/3
6
Set to 1 to configure AIN2 and AIN3 for unipolar differential conversion.
UCH4/5
5
Set to 1 to configure AIN4 and AIN5 for unipolar differential conversion.
UCH6/7
4
Set to 1 to configure AIN6 and AIN7 for unipolar differential conversion.
UCH8/9
3
Set to 1 to configure AIN8 and AIN9 for unipolar differential conversion (MAX1229/MAX1231 only).
UCH10/11
2
Set to 1 to configure AIN10 and AIN11 for unipolar differential conversion (MAX1229/MAX1231 only).
UCH12/13
1
Set to 1 to configure AIN12 and AIN13 for unipolar differential conversion (MAX1231 only).
UCH14/15
0 (LSB)
Set to 1 to configure AIN14 and AIN15 for unipolar differential conversion (MAX1231 only).
Table 5. Bipolar Mode Register (Addressed Through Setup Register)
BIT NAME
BIT
BCH0/1
7 (MSB)
Set to 1 to configure AIN0 and AIN1 for bipolar differential conversion.
FUNCTION
BCH2/3
6
Set to 1 to configure AIN2 and AIN3 for bipolar differential conversion.
BCH4/5
5
Set to 1 to configure AIN4 and AIN5 for bipolar differential conversion.
BCH6/7
4
Set to 1 to configure AIN6 and AIN7 for bipolar differential conversion.
BCH8/9
3
Set to 1 to configure AIN8 and AIN9 for bipolar differential conversion (MAX1229/MAX1231 only).
BCH10/11
2
Set to 1 to configure AIN10 and AIN11 for bipolar differential conversion (MAX1229/MAX1231 only).
BCH12/13
1
Set to 1 to configure AIN12 and AIN13 for bipolar differential conversion (MAX1231 only).
BCH14/15
0 (LSB)
Set to 1 to configure AIN14 and AIN15 for bipolar differential conversion (MAX1231only).
______________________________________________________________________________________
15
MAX1227/MAX1229/MAX1231
Temperature Measurements
The MAX1227/MAX1229/MAX1231 perform temperature measurements with an internal diode-connected
transistor. The diode bias current changes from 68µA
to 4µA to produce a temperature-dependent bias voltage difference. The second conversion result at 4µA is
subtracted from the first at 68µA to calculate a digital
value that is proportional to absolute temperature. The
output data appearing at DOUT is the above digital
code minus an offset to adjust from Kelvin to Celsius.
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Table 6. Averaging Register*
BIT NAME
BIT
—
7 (MSB)
Set to zero to select averaging register.
FUNCTION
—
6
Set to zero to select averaging register.
Set to 1 to select averaging register.
—
5
AVGON
4
Set to 1 to turn averaging on. Set to zero to turn averaging off.
NAVG1
3
Configures the number of conversions for single-channel scans.
NAVG0
2
Configures the number of conversions for single-channel scans.
NSCAN1
1
Single-channel scan count. (Scan mode 10 only.)
NSCAN0
0 (LSB)
Single-channel scan count. (Scan mode 10 only.)
*See below for bit details.
AVGON
NAVG1
NAVG0
FUNCTION
0
x
x
Performs 1 conversion for each requested result.
1
0
0
Performs 4 conversions and returns the average for each requested result.
1
0
1
Performs 8 conversions and returns the average for each requested result.
1
1
0
Performs 16 conversions and returns the average for each requested result.
1
1
1
Performs 32 conversions and returns the average for each requested result.
NSCAN1
NSCAN0
0
0
Scans channel N and returns 4 results.
0
1
Scans channel N and returns 8 results.
1
0
Scans channel N and returns 12 results.
1
1
Scans channel N and returns 16 results.
FUNCTION (APPLIES ONLY IF SCAN MODE 10 IS SELECTED)
Table 7. Reset Register
BIT NAME
BIT
—
7 (MSB)
Set to zero to select reset register.
—
6
Set to zero to select reset register.
—
5
Set to zero to select reset register.
16
FUNCTION
—
4
Set to 1 to select reset register.
RESET
3
Set to zero to reset all registers. Set to 1 to clear the FIFO only.
x
2
Reserved. Don’t care.
x
1
Reserved. Don’t care.
x
0 (LSB)
Reserved. Don’t care.
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
the internal oscillator. See Figure 5 for clock mode 01
timing.
Performing Conversions in Clock Mode 00
In clock mode 00, the wake-up, acquisition, conversion,
and shutdown sequences are initiated through CNVST
and performed automatically using the internal oscillator. Results are added to the internal FIFO to be read
out later. See Figure 4 for clock mode 00 timing.
Setting CNVST low begins an acquisition, wakes up the
ADC, and places it in track mode. Hold CNVST low for
at least 1.4µs to complete the acquisition. If internal reference needs to wake up, an additional 65µs is
required for the internal reference to power up. If a temperature measurement is being requested, reference
power-up and temperature measurement are internally
timed. In this case, hold CNVST low for at least 40ns.
Initiate a scan by setting CNVST low for at least 40ns
before pulling it high again. The MAX1227/MAX1229/
MAX1231 then wake up, scan all requested channels,
store the results in the FIFO, and shut down. After the
scan is complete, EOC is pulled low and the results are
available in the FIFO. Wait until EOC goes low before
pulling CS low to communicate with the serial interface.
EOC stays low until CS or CNVST is pulled low again. A
temperature measurement result, if requested, precedes all other FIFO results.
Do not initiate a second CNVST before EOC goes low;
otherwise, the FIFO can become corrupted.
Externally Timed Acquisitions and
Internally Timed Conversions with CNVST
Performing Conversions in Clock Mode 01
In clock mode 01, conversions are requested one at a
time using CNVST and performed automatically using
Set CNVST high to begin a conversion. After the conversion is complete, the ADC shuts down and pulls
EOC low. EOC stays low until CS or CNVST is pulled
low again. Wait until EOC goes low before pulling CS or
CNVST low.
If averaging is turned on, multiple CNVST pulses need
to be performed before a result is written to the FIFO.
Once the proper number of conversions has been performed to generate an averaged FIFO result, as specified by the averaging register, the scan logic
automatically switches the analog input multiplexer to
the next-requested channel. If a temperature measurement is programmed, it is performed after the first rising
edge of CNVST following the input data byte written to
the conversion register. The result is available on DOUT
once EOC has been pulled low.
CNVST
(UP TO 514 INTERNALLY CLOCKED ACQUISITIONS AND CONVERSIONS)
CS
SCLK
DOUT
MSB1
LSB1
MSB2
EOC
SET CNVST LOW FOR AT LEAST 40ns TO BEGIN A CONVERSION.
Figure 4. Clock Mode 00
______________________________________________________________________________________
17
MAX1227/MAX1229/MAX1231
Internally Timed Acquisitions and
Conversions Using CNVST
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
CNVST
(CONVERSION2)
(ACQUISITION1)
(ACQUISITION2)
CS
(CONVERSION1)
SCLK
DOUT
LSB1
MSB1
MSB2
EOC
REQUEST MULTIPLE CONVERSIONS BY SETTING CNVST LOW FOR EACH CONVERSION.
Figure 5. Clock Mode 01
(CONVERSION BYTE)
DIN
(UP TO 514 INTERNALLY CLOCKED ACQUISITIONS AND CONVERSIONS)
CS
SCLK
DOUT
MSB1
LSB1
MSB2
EOC
THE CONVERSION BYTE BEGINS THE ACQUISITION. CNVST IS NOT REQUIRED.
Figure 6. Clock Mode 10
Internally Timed Acquisitions and
Conversions Using the Serial Interface
Performing Conversions in Clock Mode 10
In clock mode 10, the wake-up, acquisition, conversion,
and shutdown sequences are initiated by writing an
input data byte to the conversion register, and are performed automatically using the internal oscillator. This is
the default clock mode upon power-up. See Figure 6
for clock mode 10 timing.
18
Initiate a scan by writing a byte to the conversion register. The MAX1227/MAX1229/MAX1231 then power up,
scan all requested channels, store the results in the
FIFO, and shut down. After the scan is complete, EOC
is pulled low and the results are available in the FIFO. If
a temperature measurement is requested, the temperature result precedes all other FIFO results. EOC stays
low until CS is pulled low again.
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
(ACQUISITION1)
(CONVERSION1)
(ACQUISITION2)
CS
SCLK
DOUT
MSB1
LSB1
MSB2
EOC
EXTERNALLY TIMED ACQUISITION, SAMPLING AND CONVERSION WITHOUT CNVST.
Figure 7. Clock Mode 11
Externally Clocked Acquisitions and
Conversions Using the Serial Interface
Performing Conversions in Clock Mode 11
In clock mode 11, acquisitions and conversions are initiated by writing to the conversion register and are performed one at a time using the SCLK as the conversion
clock. Scanning and averaging are disabled, and the
conversion result is available at DOUT during the conversion. See Figure 7 for clock mode 11 timing.
Initiate a conversion by writing a byte to the conversion
register followed by 16 SCLK cycles. If CS is pulsed
high between the eighth and ninth cycles, the pulse
width must be less than 100µs. To continuously convert
at 16 cycles per conversion, alternate 1 byte of zeros
between each conversion byte.
If reference mode 00 is requested, or if an external reference is selected but a temperature measurement is
being requested, wait 65µs with CS high after writing
the conversion byte to extend the acquisition and allow
the internal reference to power up. To perform a temperature measurement, write 24 bytes (192 cycles) of
zeros after the conversion byte. The temperature result
appears on DOUT during the last 2 bytes of the 192
cycles.
Partial Reads and Partial Writes
If the first byte of an entry in the FIFO is partially read
(CS is pulled high after fewer than eight SCLK cycles),
the second byte of data that is read out contains the
next 8 bits (not b7–b0). The remaining bits are lost for
that entry. If the first byte of an entry in the FIFO is read
out fully, but the second byte is read out partially, the
rest of the entry is lost. The remaining data in the FIFO
is uncorrupted and can be read out normally after taking CS low again, as long as the 4 leading bits (normally zeros) are ignored. Internal registers that are written
partially through the SPI contain new values, starting at
the MSB up to the point that the partial write is stopped.
The part of the register that is not written contains previously written values. If CS is pulled low before EOC
goes low, a conversion cannot be completed and the
FIFO is corrupted.
Transfer Function
Figure 8 shows the unipolar transfer function for singleended or differential inputs. Figure 9 shows the bipolar
transfer function for differential inputs. Code transitions
occur halfway between successive-integer LSB values.
Output coding is binary, with 1 LSB = VREF / 2.5V for
unipolar and bipolar operation, and 1 LSB = 0.125°C
for temperature measurements.
Layout, Grounding, and Bypassing
For best performance, use PC boards. Do not use wirewrap boards. Board layout should ensure that digital
and analog signal lines are separated from each other.
Do not run analog and digital (especially clock) signals
parallel to one another or run digital lines underneath the
MAX1227/MAX1229/MAX1231 package. High-frequency noise in the VDD power supply can affect performance. Bypass the VDD supply with a 0.1µF capacitor
to GND, close to the VDD pin. Minimize capacitor lead
lengths for best supply-noise rejection. If the power supply is very noisy, connect a 10Ω resistor in series with
the supply to improve power-supply filtering. For the
QFN package, connect its exposed pad to ground.
______________________________________________________________________________________
19
MAX1227/MAX1229/MAX1231
(CONVERSION BYTE)
DIN
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
OUTPUT CODE
OUTPUT CODE
FULL-SCALE
TRANSITION
11 . . . 111
11 . . . 110
011 . . . 111
FS = VREF + VCOM
2
011 . . . 110
ZS = COM
11 . . . 101
000 . . . 010
000 . . . 001
FS = VREF + VCOM
ZS = VCOM
V
1 LSB = REF
4096
00 . . . 011
00 . . . 010
-VREF
+ VCOM
2
VREF
1 LSB =
4096
-FS =
000 . . . 000
111 . . . 111
111 . . . 110
111 . . . 101
100 . . . 001
00 . . . 001
100 . . . 000
00 . . . 000
0 1
(COM)
2
3
FS
INPUT VOLTAGE (LSB)
FS - 3/2 LSB
*VCOM ≥ VREF / 2
Figure 8. Unipolar Transfer Function, Full Scale (FS) = VREF
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 MAX1227/MAX1229/MAX1231 is measured using
the end-point method.
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.
Aperture Jitter
Aperture jitter (tAJ) is the sample-to-sample variation in
the time between the samples.
Aperture Delay
Aperture delay (t AD ) is the time between the rising
edge of the sampling clock and the instant when an
actual sample is taken.
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 quanti20
- FS
COM*
+FS - 1 LSB
INPUT VOLTAGE (LSB)
Figure 9. Bipolar Transfer Function, Full Scale (±FS) = ±VREF / 2
zation error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused by quantization
error only and results directly from the ADC’s resolution
(N bits):
SNR = (6.02 x N + 1.76)dB
In reality, there are other noise sources besides quantization 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 fundamental, the first five harmonics, and the DC offset.
Signal-to-Noise Plus Distortion
Signal-to-noise plus distortion (SINAD) is the ratio of the
fundamental input frequency’s RMS amplitude to the
RMS equivalent of all other ADC output signals:
SINAD (dB) = 20 x log (SignalRMS / NoiseRMS)
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 error consists of quantization noise only. With an input range equal to the fullscale range of the ADC, calculate the effective number
of bits as follows:
ENOB = (SINAD - 1.76) / 6.02
______________________________________________________________________________________
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference

THD = 20 x log 

(V
2
2
)

+ V32 + V42 + V52 / V1

where V1 is the fundamental amplitude, and V2–V5 are
the amplitudes of the first five 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 distortion component.
Ordering Information (continued)
PART
TEMP RANGE
PIN-PACKAGE
MAX1227BCEE-T
0°C to +70°C
16 QSOP
MAX1227BEEE-T
-40°C to +85°C
16 QSOP
MAX1229ACEP-T*
0°C to +70°C
20 QSOP
MAX1229AEEP-T*
-40°C to +85°C
20 QSOP
MAX1229BCEP-T
0°C to +70°C
20 QSOP
MAX1229BEEP-T
-40°C to +85°C
20 QSOP
MAX1231ACEG-T*
0°C to +70°C
24 QSOP
MAX1231AEEG-T*
-40°C to +85°C
24 QSOP
MAX1231BCEG-T
0°C to +70°C
24 QSOP
MAX1231BEEG-T
-40°C to +85°C
24 QSOP
MAX1231BCGI-T*
0°C to +70°C
28 QFN-EP**
MAX1231BEGI-T*
-40°C to +85°C
28 QFN-EP**
*Future product—contact factory for availability.
**EP = Exposed paddle (connect to GND).
Chip Information
TRANSISTOR COUNT: 30,889
PROCESS: BiCMOS
Pin Configurations (continued)
16 CNVST/AIN15
AIN9 10
15 REF-/AIN14
AIN10 11
14 AIN13
AIN11 12
13 AIN12
QSOP
AIN1
AIN0
N.C.
EOC
DOUT
DIN
27
26
25
24
23
22
4
18
VDD
AIN6
5
17
N.C.
AIN7
6
16
GND
AIN8
7
15
REF+
14
AIN8 9
AIN5
CNVST/AIN15
17 REF+
N.C.
13
AIN7 8
19
MAX1231
REF-/AIN14
18 GND
3
12
AIN6 7
AIN4
AIN13
19 VDD
AIN5 6
SCLK
11
20 SCLK
CS
20
AIN12
MAX1231
21
2
10
AIN4 5
21 CS
1
AIN11
AIN3 4
N.C.
AIN3
9
22 DIN
AIN10
AIN2 3
AIN2
23 DOUT
8
24 EOC
AIN1 2
AIN9
AIN0 1
28
TOP VIEW
QFN
______________________________________________________________________________________
21
MAX1227/MAX1229/MAX1231
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:
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 www.maxim-ic.com/packages.)
QSOP.EPS
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
PACKAGE OUTLINE, QSOP .150", .025" LEAD PITCH
21-0055
22
E
1
______________________________________________________________________________________
1
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
32L QFN.EPS
PACKAGE OUTLINE, 16,20,28,32L QFN,
5x5x0.90 MM
1
21-0091
I
2
______________________________________________________________________________________
23
MAX1227/MAX1229/MAX1231
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
MAX1227/MAX1229/MAX1231
12-Bit 300ksps ADCs with FIFO,
Temp Sensor, Internal Reference
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE, 16,20,28,32L QFN,
5x5x0.90 MM
2
21-0091
I
2
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.
24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.