8-Channel, I2C, 12-Bit SAR ADC
with Temperature Sensor
Enhanced Product
AD7291-EP
Rev. 0 Document Feedback
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FEATURES
12-bit SAR ADC
8 single-ended analog input channels
Analog input range: 0 V to 2.5 V
12-bit temperature to digital converter
Temperature sensor accuracy of ±1°C typical
Channel sequencer operation
Specified for VDD of 2.8 V to 3.6 V
Logic voltage VDRIVE = 1.65 V to 3.6 V
Internal 2.5 V reference
I2C-compatible serial interface supports standard and
fast speed modes
Out of range indicator/alert function
Autocycle mode
Power-down current: 13 µA maximum
20-lead LFCSP package
ENHANCED PRODUCT FEATURES
Supports defense and aerospace applications (AQEC
standard)
Extended industrial temperature range: −55°C to +125°C
Controlled manufacturing baseline
1 assembly/test site
1 fabrication site
Product change notification
Qualification data available upon request
FUNCTIONAL BLOCK DIAGRAM
TEMP
SENSOR
12-BIT
SUCCESSIVE
APPROXIMATION
ADC
INPUT
MUX
T/H
V
DD
GND
PD/RST
SCL
SDA
AS1
AS0
V
DRIVE
V
IN7
V
IN0
CONTROL LOGIC
I
2
C INTERF ACE
SEQUENCER
V
REF
BUFREF
AD7291-EP
15915-001
ALERT
Figure 1.
GENERAL DESCRIPTION
The AD7291-EP is a 12-bit, low power, 8-channel, successive
approximation analog-to-digital converter (ADC) with an
internal temperature sensor.
The device operates from a single 3.3 V power supply and
features an I2C-compatible interface. The device contains a
9-channel multiplexer and a track-and-hold amplifier with an
input bandwidth of 30 MHz. The device has an on-chip 2.5 V
reference that can be disabled to allow the use of an external
reference.
The AD7291-EP provides a 2-wire serial interface compatible
with I2C interfaces. The I2C interface supports standard and fast
I2C interface modes. The AD7291-EP normally remains in a
partial power-down state while not converting and powers up
for conversions. The conversion process can be controlled by a
command mode where conversions occur across I2C write
operations or an autocycle mode selected through software control.
The AD7291-EP includes a high accuracy band gap temperature
sensor, which is monitored and digitized by the 12-bit ADC to
give a resolution of 0.25°C.
The AD7291-EP offers a programmable sequencer, which
enables the selection of a preprogrammable sequence of
channels for conversion.
On-chip limit registers can be programmed with high and low
limits for the conversion results; an out-of-range indicator output
(ALERT) becomes active when the programmed high or low
limits are violated by the conversion result. This output can be
used as an interrupt.
Additional application and technical information can be found
in the AD7291 data sheet.
AD7291-EP Enhanced Product
Rev. 0 | Page 2 of 8
TABLE OF CONTENTS
Features .............................................................................................. 1
Enhanced Product Features ............................................................ 1
Functional Block Diagram .............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 5
Thermal Resistance .......................................................................5
ESD Caution...................................................................................5
Pin Configuration and Function Descriptions ..............................6
Typical Performance Characteristics ..............................................7
Outline Dimensions ..........................................................................8
Ordering Guide .............................................................................8
REVISION HISTORY
7/2017—Revision 0: Initial Version
Enhanced Product AD7291-EP
Rev. 0 | Page 3 of 8
SPECIFICATIONS
VDD = 2.8 V to 3.6 V; VDRIVE = 1.65 V to 3.6 V; fSCL = 400 kHz, fast SCLK mode; VREF = 2.5 V internal/external; TA = −55°C to +125°C,
unless otherwise noted.
Table 1.
Parameter Min Typ Max Unit1 Test Conditions/Comments
DYNAMIC PERFORMANCE
f
IN
= 1 kHz sine wave
Signal-to-Noise Ratio (SNR) 70 71 dB
Signal-to-Noise + Distortion Ratio (SINAD) 70 71 dB
Total Harmonic Distortion (THD) −84 −78 dB
Spurious-Free Dynamic Range (SFDR) −85 −80 dB
Intermodulation Distortion (IMD)
f
A
= 5.4 kHz, f
B
= 4.6 kHz
Second-Order Terms −88 dB
Third-Order Terms −88 dB
Channel-to-Channel Isolation −100 dB fIN = 10 kHz
Full Power Bandwidth2 30 MHz At 3 dB
10 MHz At 0.1 dB
DC ACCURACY
Resolution 12 Bits
Integral Nonlinearity (INL) ±0.5 ±1 LSB
Differential Nonlinearity (DNL)
±0.5
LSB
Guaranteed no missing codes to 12 bits
Offset Error ±2 ±4.5 LSB
Offset Error Matching ±2.5 ±4.5 LSB
Offset Temperature Drift 4 ppm/°C
Gain Error ±1 ±4 LSB
Gain Error Matching
±1
LSB
Gain Temperature Drift 0.5 ppm/°C
ANALOG INPUT
Input Voltage Ranges 0 VREF V
DC Leakage Current ±0.01 ±1 µA
Input Capacitance2 34 pF When in track
8 pF When in hold
REFERENCE INPUT/OUTPUT
Reference Output Voltage3 2.4925 2.5 2.5075 V ±0.3% maximum at 25°C
Long-Term Stability 150 ppm For 1000 hours
Output Voltage Hysteresis 50 ppm
Reference Input Voltage Range4 1 2.5 V
DC Leakage Current ±0.01 ±1 µA External reference applied to Pin VREF
VREF Output Impedance 1 Ω
Reference Temperature Coefficient 12 35 ppm/°C
VREF Noise2 60 µV rms Bandwidth = 10 MHz
LOGIC INPUTS (SDA, SCL)
Input High Voltage, VINH 0.7 × VDRIVE V
Input Low Voltage, VINL 0.3 × VDRIVE V
Input Current, IIN ±0.01 ±1 µA VIN = 0 V or VDRIVE
Input Capacitance, C
IN2
6
pF
Input Hysteresis, VHYST 0.1 × VDRIVE V
AD7291-EP Enhanced Product
Rev. 0 | Page 4 of 8
Parameter Min Typ Max Unit1 Test Conditions/Comments
LOGIC OUTPUTS
Output High Voltage, VOH VDRIVE − 0.3 V VDRIVE < 1.8
VDRIVE − 0.2 V VDRIVE ≥ 1.8
Output Low Voltage, VOL 0.4 V ISINK = 3 mA
V
I
SINK
= 6 mA
Floating State Leakage Current ±0.01 ±1 µA
Floating State Output Capacitance2 8 pF
INTERNAL TEMPERATURE SENSOR
Operating Range −55 +125 °C
Accuracy ±1 ±2 °C TA = −55°C to +85°C
±1 ±3 °C TA = 85°C to 125°C
Resolution 0.25 °C LSB size
CONVERSION RATE
Conversion Time 3.2 μs
Autocycle Update Rate5 50 μs
Throughput Rate
kSPS
f
SCL
= 400 kHz
POWER REQUIREMENTS Digital inputs = 0 V or VDRIVE
VDD 2.8 3 3.6 V
VDRIVE 1.65 3 3.6 V
ITOTAL 6, 7
Normal Mode (Operational) 2.9 3.5 mA
Normal Mode (Static) 2.9 3.4 mA
Full Power-Down Mode 0.3 1.6 μA TA = −55°C to +25°C
1.6 4.5 μA TA = >25°C to 85°C
4.9
μA
T
A
= >85°C to 125°C
Power Dissipation7
Normal Mode (Operational) 8.7 10.5 mW VDD = 3 V, VDRIVE = 3 V
10.4 12.6 mW
Normal Mode (Static) 10.4 12.2 mW
Full Power-Down Mode
1.1
µW
T
A
= −55°C to +25°C
5.8 16.2 µW TA = >25°C to 85°C
17.6 46.8 µW TA = >85°C to 125°C
1 All specifications expressed in decibels are referred to full-scale range (FSR) and tested with an input signal at 0.5 dB below full scale, unless otherwise specified.
2 Sample tested during initial product release to ensure compliance.
3 Refers to Pin VREF specified for 25oC.
4 A correction factor can be required on the temperature sensor results when using an external VREF (see the AD7291 data sheet).
5 Sampled during initial product release to ensure compliance; not subject to production testing.
6 ITOTAL is the total current flowing in VDD and VDRIVE.
7 ITOTAL and power dissipation are specified with VDD = VDRIVE = 3.6 V, unless otherwise noted.
Enhanced Product AD7291-EP
Rev. 0 | Page 5 of 8
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
VDD to GND1, GND −0.3 V to +5 V
V
DRIVE
to GND1, GND
−0.3 V to +5 V
Analog Input Voltage to GND1 −0.3 V to +3 V
Digital Input Voltage to GND1 −0.3 V to VDRIVE + 0.3 V
Digital Output Voltage to GND1 −0.3 V to VDRIVE + 0.3 V
VREF to GND1 −0.3 V to +3 V
GND to GND1 −0.3 V to +0.3 V
Input Current to Any Pin Except Supplies1 ±10 mA
Operating Temperature Range −55°C to +125°C
Storage Temperature Range −65°C to +150°C
Junction Temperature 150°C
Pb-free Temperature, Soldering
Reflow 260(+0)°C
ESD 2 kV
1 Transient currents of up to 100 mA do not cause latch-up.
Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at these
or any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.
THERMAL RESISTANCE
Thermal performance is directly linked to printed circuit board
(PCB) design and operating environment. Close attention to
PCB thermal design is required.
Table 3. Thermal Resistance
Package Type
θ
JA
θ
JC
Unit
CP-20-81 52 6.5 °C/W
1 Thermal impedance simulated values are based on JEDEC 2S2P thermal test
board with 9 thermal vias. See JEDEC JESD51.
ESD CAUTION
AD7291-EP Enhanced Product
Rev. 0 | Page 6 of 8
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
14
13
12
1
3
4
SDA
15 SCL
AS1
ALERT
11AS0
VIN3
VIN5
2
VIN4
VIN6
5
VIN7
7
V
REF
6
GND1
8
D
CAP
9
GND
10
V
DD
19
V
IN1
20
V
IN2
18
V
IN0
17
PD/RST
16
V
DRIVE
15915-002
NOTES
1. THE EXPOSED METAL PADDLE ON THE BOTTOM
OF THE LF CS P P ACKAGE S HOUL D BE S OL DE RE D
TO P CB GRO UND FO R P ROPE R HE AT DI S S IPAT IO N
AND PERF ORMANCE .
TOP VIEW
(Not to S cale)
AD7291-EP
Figure 2. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 to 5,
18 to 20
VIN3, VIN4,
VIN5, VIN6,
VIN7, VIN0,
VIN1, VIN2
Analog Inputs. The AD7291-EP has eight single-ended analog inputs that are multiplexed into the on-chip track-
and-hold amplifier. Each input channel can accept analog inputs from 0 V to 2.5 V. Any unused input channels
must be connected to GND1 to avoid noise pickup.
6
GND1
Ground. Ground reference point for the internal reference circuitry on the AD7291-EP. All analog input signals and
the external reference signals must be referred to this GND1 voltage. The GND1 pin must be connected to the
ground plane of a system. All ground pins must ideally be at the same potential and must not be more than 0.3 V
apart, even on a transient basis. The VREF pin must be decoupled to this ground pin via a 10 μF decoupling capacitor.
7 VREF Internal Reference/External Reference Supply. The nominal internal reference voltage of 2.5 V appears at this pin.
Provided the output is buffered, the on-
chip reference can be taken from this pin and applied externally to the rest
of a system. Decoupling capacitors must be connected to this pin to decouple the reference buffer. For best
performance, it is recommended to use a 10 μF decoupling capacitor on this pin to GND1. The internal reference
can be disabled and an external reference supplied to this pin if required. The input voltage range for the external
reference is 2.0 V to 2.5 V.
8 DCAP Decoupling Capacitor Pin. Decoupling capacitors (1 μF recommended) are connected to this pin to decouple the
internal low dropout regulator (LDO).
9 GND Ground. Ground reference point for all analog and digital circuitry on the AD7291-EP. The GND pin must be con-
nected to the ground plane of the system. All ground pins must ideally be at the same potential and must not be
more than 0.3 V apart, even on a transient basis. Both DCAP and VDD pins must be decoupled to this GND pin.
10 VDD Supply Voltage, 2.8 V to 3.6 V. This supply must be decoupled to GND with 10 μF and 100 nF decoupling capacitors.
11, 13 AS0, AS1 Logic Inputs. Together, the logic state of these two inputs selects a unique I2C address for the AD7291-EP. See the
AD7291 data sheet for details. The device address depends on the voltage applied to these pins.
12 ALERT Digital Output. This pin acts as an out-of-range indicator and, if enabled, becomes active when the conversion
result violates the DATAHIGH or DATALOW register values. See the AD7291 data sheet for further details.
14 SDA Digital Input/Output. Serial bus bidirectional data. This open-drain output requires a pull-up resistor. The output
coding is straight binary for the voltage channels and twos complement for the temperature sensor result.
15 SCL Digital Inputs. Serial I2C Bus Clock. This input requires a pull-up resistor. The data transfer rate in I2C mode is
compatible with both 100 kHz and 400 kHz operating modes.
16 VDRIVE Logic Power Supply Input. The voltage supplied at this pin determines the voltage at which the interface operates.
This pin must be decoupled to GND. The voltage range on this pin is 1.65 V to 3.6 V and can be less than the
voltage at VDD but must never exceed it by more than 0.3 V.
17 PD/
RST Power-Down Pin. This pin places the device into a full power-down mode and enables power conservation when
operation is not required. This pin can be used to reset the device by toggling the pin low for a minimum of 1 ns and a
maximum of 100 ns. If the maximum time is exceeded, the device enters power-down mode. When placing the device
in full power-down mode, the analog inputs must be returned to 0 V.
EPAD EPAD Exposed Pad. The exposed metal paddle on the bottom of the LFCSP package must be soldered to PCB ground for
proper functionality and heat dissipation.
Enhanced Product AD7291-EP
Rev. 0 | Page 7 of 8
TYPICAL PERFORMANCE CHARACTERISTICS
–1.5
–1.0
–0.5
0
0.5
1.0
1.5
–55 –40 –25 –10 520 35 55 65 80 95 110 125
TEM P E RATURE E RROR (°C)
TEMPERATURE (°C)
15915-003
Figure 3. Temperature Accuracy at 3 V
0
1
2
3
4
5
6
7
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6
TOTAL CURRENT (µA)
VDD (V)
–55°C
+25°C
+85°C
+125°C
VDRIVE = 3V
15915-004
Figure 4. Full Shutdown Current vs. Supply Voltage for Various Temperatures
AD7291-EP Enhanced Product
Rev. 0 | Page 8 of 8
OUTLINE DIMENSIONS
0.50
BSC
0.50
0.40
0.30
0.30
0.25
0.18
COMPLIANT
TO
JEDEC STANDARDS M O-220- WG GD-11.
4.10
4.00 SQ
3.90
0.80
0.75
0.70 0. 05 M AX
0.02 NO M
0.20 REF
0.25 MIN
COPLANARITY
0.08
PIN 1
INDICATOR
2.75
2.60 SQ
2.35
1
20
6
10
11
15
16
5
BOTTOM VIEW
TOP VIEW
SIDE VIEW FO R P ROPE R CONNECTI ON O F
THE EXPOSED PAD, REFER TO
THE P IN CO NFI GURAT IO N AND
FUNCT IO N DE S CRIPTI ONS
SECTION OF THIS DATA SHEET.
02-21-2017-B
EXPOSED
PAD
PKG-005089
SEATING
PLANE
PIN 1
INDIC ATOR AREA OPTIONS
(SEE DETAIL A)
DETAIL A
(JEDEC 95)
Figure 5. 20-Lead Lead Frame Chip Scale Package [LFCSP]
4 mm × 4 mm Body and 0.75 mm Package Height
(CP-20-8)
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
AD7291TCPZ-EP −55°C to +125°C 20-Lead Lead Frame Chip Scale Package [LFCSP] CP-20-8
AD7291TCPZ-EP-RL7 −55°C to +125°C 20-Lead Lead Frame Chip Scale Package [LFCSP] CP-20-8
1 Z = RoHS Compliant Part.
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
©2017 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D15915-0-7/17(0)