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LMP91050
SNAS517E – NOVEMBER 2011 – REVISED SEPTEMBER 2015
LMP91050 Configurable AFE for Nondispersive Infrared (NDIR) Sensing Applications
1 Features
3 Description
•
•
•
•
•
The LMP91050 device is a programmable integrated
Sensor Analog Front End (AFE) optimized for
thermopile sensors, as typically used in NDIR
applications. It provides a complete signal path
solution between a sensor and microcontroller that
generates an output voltage proportional to the
thermopile voltage. The programmability of the
LMP91050 enables it to support multiple thermopile
sensors with a single design as opposed to the
multiple discrete solutions.
1
Programmable Gain Amplifier
Dark Signal Offset Cancellation
Supports External Filtering
Common-Mode Generator and 8-Bit DAC
Key Specifications
– Programmable Gain 167 to 7986 V/V
– Low Noise (0.1 to 10 Hz) 0.1 μVRMS
– Gain Drift 100 ppm/°C (Maximum)
– Phase Delay Drift 500 ns (Maximum)
– Power Supply Voltage Range 2.7 to 5.5 V
The LMP91050 features a programmable gain
amplifier (PGA), dark phase offset cancellation, and
an adjustable common-mode generator (1.15 V or
2.59 V) which increases output dynamic range. The
PGA offers a low-gain range of 167 V/V to 1335 V/V
plus a high-gain range of 1002 V/V to 7986 V/V which
enables the user to use thermopiles with different
sensitivities. The PGA is highlighted by low-gain drift
(100 ppm/°C), output offset drift (1.2 mV/°C at G =
1002 V/V), phase delay drift (500 ns) and noise
specifications (0.1 μVRMS 0.1 to 10Hz).
2 Applications
•
•
•
•
•
•
•
NDIR Sensing
Demand Control Ventilation
Building Monitoring
CO2 Cabin Control — Automotive
Alcohol Detection — Automotive
Industrial Safety and Security
GHG and Freons Detection Platforms
Device Information(1)
PART NUMBER
LMP91050
PACKAGE
VSSOP (10)
BODY SIZE (NOM)
3.00 mm × 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application Circuit
10 µF
6.8 nF
160 k
VDD
10 µF
CMOUT
10 nF
VDD
Thermopile
160 k
A0
A1
OUT
IN
1 kO
û ADC
10 nF
LMP91050
1 µF
CSB
CMOUT
SCLK
SDIO
10 nF
GND
Configurable AFE for NDIR
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LMP91050
SNAS517E – NOVEMBER 2011 – REVISED SEPTEMBER 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Description (continued).........................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
3
7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
3
4
4
4
4
6
6
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
SPI Interface .............................................................
Timing Characteristics .............................................
Typical Characteristics ..............................................
Detailed Description ............................................ 12
8.1 Overview ................................................................. 12
8.2 Functional Block Diagram ....................................... 12
8.3
8.4
8.5
8.6
9
Feature Description.................................................
Device Functional Modes........................................
Programming...........................................................
Register Maps .........................................................
12
14
14
16
Application and Implementation ........................ 18
9.1 Application Information............................................ 18
9.2 Typical Application ................................................. 18
10 Power Supply Recommendations ..................... 21
11 Layout................................................................... 21
11.1 Layout Guidelines ................................................. 21
11.2 Layout Example .................................................... 21
12 Device and Documentation Support ................. 22
12.1
12.2
12.3
12.4
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
22
22
22
22
13 Mechanical, Packaging, and Orderable
Information ........................................................... 22
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (March 2013) to Revision E
•
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
Changes from Revision C (April 2012) to Revision D
•
2
Page
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 17
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5 Description (continued)
The offset cancellation circuitry compensates for the dark signal by adding an equal and opposite offset to the
input of the second stage, thus removing the original offset from the output signal. This offset cancellation
circuitry allows optimized usage of the ADC full scale and relaxes ADC resolution requirements.
The LMP91050 allows extra signal filtering (high-pass, lowpass or bandpass) through dedicated pins A0 and A1,
in order to remove out of band noise. The user can program through the on board SPI interface. Available in a
small form factor 10-pin package, the LMP91050 operates from –40 to 105°C.
6 Pin Configuration and Functions
DGS Package
10-Pin VSSOP
Top View
VDD
IN
SDIO
CMOUT
A0
LMP91050
SCLK
A1
CSB
GND
OUT
Pin Functions
PIN
NO.
NAME
TYPE
DESCRIPTION
1
IN
Analog Input
2
CMOUT
Analog Output
Signal Input
Common-Mode Voltage Output
3
A0
Analog Output
First Stage Output
4
A1
Analog Input
5
GND
Power
6
OUT
Analog Output
7
CSB
Digital Input
Chip Select, active low
8
SCLK
Digital Input
Interface Clock
9
SDIO
10
VDD
Second Stage Input
Ground
Signal Output, reference to the same potential as CMOUT
Digital Input / Output Serial Data Input / Output
Power
Positive Supply
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2) (3)
MIN
MAX
UNIT
Supply Voltage (VDD)
–0.3
6
V
Voltage at Any Pin
–0.3
VDD + 0.3
V
5
mA
150
°C
150
°C
Input Current at Any Pin
Junction Temperature (4)
Storage Temperature, Tstg
(1)
(2)
(3)
(4)
–65
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
For soldering specifications: see product folder at www.ti.com and SNOA549.
The maximum power dissipation is a function of TJ(MAX), θJA, and the ambient temperature, TA. The maximum allowable power
dissipation at any ambient temperature is PDMAX = (TJ(MAX) - TA)/ θJA All numbers apply for packages soldered directly onto a PC
board.
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SNAS517E – NOVEMBER 2011 – REVISED SEPTEMBER 2015
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7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2500
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±1250
Machine Model
±250
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
Supply Voltage
2.7
5.5
V
Junction Temperature (2)
–40
105
°C
(1)
(2)
UNIT
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
The maximum power dissipation is a function of TJ(MAX), θJA, and the ambient temperature, TA. The maximum allowable power
dissipation at any ambient temperature is PDMAX = (TJ(MAX) - TA)/ θJA All numbers apply for packages soldered directly onto a PC board.
7.4 Thermal Information
LMP91050
THERMAL METRIC
(1)
DGS (VSSOP)
UNIT
10 PINS
RθJA
(1)
Junction-to-ambient thermal resistance
176
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
7.5 Electrical Characteristics
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, unless otherwise specified. All other limits apply to TA = TJ
= +25°C. (1)
PARAMETER
TEST CONDITIONS
MIN (2)
TYP (3)
MAX (2)
UNIT
POWER SUPPLY
VDD
Supply voltage
2.7
3.3
5.5
V
IDD
Supply current
All analog block ON
3.1
3.7
4.2
mA
Power-down supply current
All analog block OFF
45
85
121
μA
OFFSET CANCELLATION (OFFSET DAC)
Resolution
LSB
256
All gains
DNL
-1
Error
Output referred offset error, all gains
Offset adjust range
Output referred, all gains
DAC settling time
steps
33.8
mV
2
±100
0.2
LSB
mV
VDD – 0.2
V
μs
480
PROGRAMMABLE GAIN AMPLIFIER (PGA) 1ST STAGE, RL = 10 kΩ, CL = 15 pF
5
IBIAS
(1)
(2)
(3)
4
Bias current
TA = –40°C to +85°C
200
pA
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped
production material.
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Electrical Characteristics (continued)
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, unless otherwise specified. All other limits apply to TA = TJ
= +25°C.(1)
PARAMETER
VINMAX
_HGM
Max input signal high-gain
mode
VINMAX
_LGM
Max input signal low-gain
mode
VOS
Input offset voltage
G _HGM
G_LGM
GE
Gain error
VOUT
Output voltage range
TEST CONDITIONS
MIN (2)
Referenced to CMOUT voltage, it refers
to the maximum voltage at the IN pin
before clipping; It includes dark voltage of
the thermopile and signal voltage.
TYP (3)
MAX (2)
UNIT
±2
mV
±12
mV
-165
µV
Gain high-gain mode
250
V/V
Gain low-gain mode
42
V/V
Both HGM and LGM
2.5%
0.5
PhDly
Phase delay
1-mV input step signal, HGM, VOUT
measured at Vdd/2
TCPhDly
Phase delay variation with
temperature
1-mV input step signal, HGM, VOUT
measured at Vdd/2,
SSBW
Small signal bandwidth
Vin = 1mVpp, Gain = 250 V/V
Cin
Input capacitance
VDD – 0.5
V
6
μs
416
ns
18
kHz
100
pF
1.65
V
0.82
V
PROGRAMMABLE GAIN AMPLIFIER (PGA) 2ND STAGE, RS = 1 kΩ, CL = 1 µF
VINMAX
Max input signal
VINMIN
Min input signal
GAIN = 4 V/V
G
Gain
Programmable in 4 steps
GE
Gain error
Any gain
VOUT
Output voltage range
4
32
V/V
2.5
0.2
%
VDD – 0.2
V
PhDly
Phase delay
100-mV input sine 35-kHz signal, Gain =
8, VOUT measured at 1.65 V, RL = 10 kΩ
TCPhDly
Phase delay variation with
temperature
250-mV input step signal, Gain = 8, VOUT
measured at Vdd/2
SSBW
Small signal bandwidth
Gain = 32 V/V
Cin
Input capacitance
CLOAD,
OUT
OUT pin load capacitance
Series RC
1
µF
RLOAD,
OUT
OUT pin load resistance
Series RC
1
kΩ
Combination of both current and voltage
noise, with a 86kΩ source impedance at
5Hz, Gain = 7986
30
nV/√Hz
Combination of both current and voltage
Input-referred integrated noise noise, with a 86kΩ source impedance
0.1Hz to 10Hz, Gain = 7986
0.1
1
µs
84
ns
360
kHz
5
pF
COMBINED AMPLIFIER CHAIN SPECIFICATION
en
G
GE
(4)
Input-referred noise density
Gain
Gain error
PGA1 GAIN = 42, PGA2 GAIN = 4
167
PGA1 GAIN = 42, PGA2 GAIN = 8
335
PGA1 GAIN = 42, PGA2 GAIN = 16
669
PGA1 GAIN = 42, PGA2 GAIN = 32
1335
PGA1 GAIN = 250, PGA2 GAIN = 4
1002
PGA1 GAIN = 250, PGA2 GAIN = 8
2004
PGA1 GAIN = 250, PGA2 GAIN = 16
4003
PGA1 GAIN = 250, PGA2 GAIN = 32
7986
Any gain
0.12 (4)
µVrms
V/V
5%
Specified by design and characterization. Not tested on shipped production material.
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Electrical Characteristics (continued)
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, unless otherwise specified. All other limits apply to TA = TJ
= +25°C.(1)
PARAMETER
TEST CONDITIONS
(5)
TCCGE
Gain temp coefficient
PSRR
Power supply rejection ratio
DC, 3-V to 3.6-V supply, gain = 1002 V/V
PhDly
Phase delay
1-mV input step signal, Gain = 1002,
VOUT measured at Vdd/2
TCPhDly
Phase delay variation with
temperature (6)
1-mV input step signal, Gain=1002, VOUT
measured at Vdd/2, TA = –40°C to +85°C
TCVOS
Output offset voltage
temperature drift (5)
MIN (2)
TYP (3)
TA = –40°C to +85°C
MAX (2)
100
90
UNIT
ppm/°C
110
dB
9
µs
500
Gain = 167 V/V, TA = –40°C to +85°C
–0.525
0.525
Gain = 335 V/V, TA = –40°C to +85°C
–0.6
0.6
Gain = 669 V/V, TA = –40°C to +85°C
–0.9
0.9
Gain = 1335 V/V, TA = –40°C to +85°C
–1.5
1.5
Gain = 1002 V/V, TA = –40°C to +85°C
–1.2
1.2
Gain = 2004 V/V, TA = –40°C to +85°C
–1.9
1.9
Gain = 4003 V/V, TA = –40°C to +85°C
–3.7
3.7
Gain = 7986V/V, TA = –40°C to +85°C
–7.1
7.1
ns
mV/°C
COMMON-MODE GENERATOR
VCM
Common-mode voltage
Programmable, see Common-Mode
Generation
1.15 or
2.59
VCM accuracy
CLOAD
(5)
(6)
V
2%
CMOut load capacitance
10
nF
TCCGE and TCVOS are calculated by taking the largest slope between -40°C and 25°C linear interpolation and 25°C and 85°C linear
interpolation.
TCPhDly is largest change in phase delay between -40°C and 25°C measurements and 25°C and 85°C measurements.
7.6 SPI Interface
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, CL = 15 pF, unless otherwise specified. All other limits
apply to TA = TJ = +25°C. (1)
PARAMETER
VIH
Logic input high
VIL
Logic input low
VOH
Logic output high
VOL
Logic output low
IIH/IIL
(1)
(2)
(3)
Input digital leakage current
TEST CONDITIONS
MIN (2)
TYP (3)
MAX (2)
0.7 × VDD
V
0.8
2.6
V
V
0.4
TA = –40°C to +85°C
UNIT
–100
100
–200
200
V
nA
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped
production material.
7.7 Timing Characteristics
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, CL = 15 pF, unless otherwise specified. All other limits
apply to TA = TJ = +25°C. (1)
(1)
6
Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very
limited self-heating of the device such that TJ = TA. No ensured specification of parametric performance is indicated in the electrical
tables under conditions of internal self-heating where TJ > TA. Absolute Maximum Ratings indicate junction temperature limits beyond
which the device may be permanently degraded, either mechanically or electrically.
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Timing Characteristics (continued)
The following specifications apply for VDD = 3.3 V, VCM = 1.15 V, CL = 15 pF, unless otherwise specified. All other limits
apply to TA = TJ = +25°C.(1)
PARAMETER
TEST CONDITIONS
MIN (2)
TYP (3)
MAX (2)
Wake-up time
fSCLK
Serial clock frequency
tPH
SCLK pulse width high
0.4 / fSCLK
ns
tPL
SCLK pulse width low
0.4 / fSCLK
ns
tCSS
CSB set-up time
10
ns
tCSH
CSB hold time
10
ns
tSU
SDI set-up time prior to rise
edge of SCLK
10
ns
tSH
SDI hold time prior to rise edge
of SCLK
10
ns
tDOD1
SDO disable time after rise
edge of CSB
45
ns
tDOD2
SDO disable time after 16th rise
edge of SCLK
45
ns
tDOE
SDO enable time from the fall
edge of 8th SCLK
35
ns
tDOA
SDO access time after the fall
edge of SCLK
35
ns
tDOH
SDO hold time after the fall
edge of SCLK
tDOR
SDO rise time
5
ns
tDOF
SDO fall time
5
ns
(2)
(3)
1
UNIT
tWU
ms
10
5
MHz
ns
Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlations using
statistical quality control (SQC) method.
Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary
over time and will also depend on the application and configuration. The typical values are not tested and are not ensured on shipped
production material.
Figure 1. SPI Timing Diagram
tPL
tPH
16th clock
SCLK
tH
tSU
SDI
Valid Data
Valid Data
Figure 2. SPI Set-Up Hold Time
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Figure 3. SDO Disable Time After 16th Rise Edge of SCLK
Figure 4. SDO Access Time (tDOA) and SDO Hold Time (tDOH) After the Fall Edge of SCLK
Figure 5. SDO Enable Time from the Fall Edge of 8th SCLK
Figure 6. SDO Disable Time after Rise Edge of CSB
Figure 7. SDO Rise and Fall Times
8
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7.8 Typical Characteristics
168.4
336.0
168.3
335.9
168.2
335.8
GAIN (V/V)
GAIN (V/V)
VDD = +3.3 V, VCM = 1.15 V, and TA = 25°C unless otherwise noted
168.1
168.0
335.6
167.9
335.5
167.8
-50
335.7
-25
0
25
50
75
TEMPERATURE (°C)
335.4
-50
100
Figure 8. Gain = 167 V/V vs. Temperature
-25
0
25
50
75
TEMPERATURE (°C)
100
Figure 9. Gain = 335 V/V vs. Temperature
672.5
1011
672.4
GAIN (V/V)
GAIN (V/V)
672.3
672.2
672.1
672.0
1010
1009
671.9
671.8
671.7
-50
1008
-25
0
25
50
75
TEMPERATURE (°C)
100
-50
2014
9.3
2013
9.2
2012
2011
2010
9.1
9.0
8.9
8.8
2009
8.7
2008
8.6
-50
-25
0
25
50
75
TEMPERATURE (°C)
100
Figure 11. Gain = 1002 V/V vs. Temperature
PHASE DELAY ( s)
GAIN (V/V)
Figure 10. Gain = 669 V/V vs. Temperature
-25
0
25
50
75
TEMPERATURE (°C)
100
Figure 12. Gain = 2004 V/V vs. Temperature
-50
-25
0
25
50
TEMPERATURE (°C)
75
100
Figure 13. Phase Delay vs. Temperature
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Typical Characteristics (continued)
VDD = +3.3 V, VCM = 1.15 V, and TA = 25°C unless otherwise noted
1.160
100
COMMON MODE VOLTAGE (V)
OUTPUT OFFSET (mV)
90
80
70
60
50
40
30
G = 1002 V/V
20
10
0
-50
-25
0
25
50
TEMPERATURE (°C)
75
1.154
1.152
0
5
-1
4
-2
-3
-25
0
25
50
75
TEMPERATURE (°C)
100
Figure 15. Common-Mode Voltage vs. Temperature
IDD (mA)
IBIAS (pA)
1.156
1.150
-50
100
Figure 14. Output Offset vs. Temperature
1.158
3
2
G = 1002 V/V
-4
1
-5
0
-50
-25
0
25
50
TEMPERATURE (°C)
75
100
-50
Figure 16. Input Bias Current vs. Temperature
-25
0
25
50
TEMPERATURE (°C)
75
100
Figure 17. Supply Current vs. Temperature
4.5
120
4.0
110
3.5
100
IDD ( A)
IDD (mA)
3.0
2.5
2.0
1.5
80
PGA ALL ON
PGA2 ON
PGA1 ON
1.0
0.5
70
0.0
2.5
60
3.0
3.5
4.0
4.5
VDD (V)
5.0
5.5
Figure 18. Supply Current vs. Supply Voltage
10
90
2.5
3.0
3.5
4.0
4.5
VDD (V)
5.0
5.5
Figure 19. Power-Down Supply Current vs. Supply Voltage
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Typical Characteristics (continued)
VDD = +3.3 V, VCM = 1.15 V, and TA = 25°C unless otherwise noted
OUTPUT OFFSET (mV)
70
G = 1002 V/V
65
60
55
50
2.5
3.0
3.5
4.0
4.5
VDD (V)
5.0
5.5
Figure 20. Output Offset vs. Supply Voltage
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8 Detailed Description
8.1 Overview
The input channel of the LMP91050 features two programmable gain stages that give the user flexibility in
optimizing the system gain. Access to the inter-stage connection between the gain blocks also allows the
inclusion of appropriate filtering if needed. The internal DAC allows the DC offset of the output voltage to be
adjusted independently of the common-mode voltage supplied to the sensor, enabling the sampled signal to be
centered within the ADC full-scale input range.
The following paragraphs discuss the LMP91050’s features in more detail.
8.2 Functional Block Diagram
CMOUT
VDD
A0
A1
LMP91050
G2=4,8,16,32
G1=250,42
IN
SPI
OUT
PGA2
PGA1
DAC
CMOUT
SPI
CM GEN
VREF
GND
CSB SCLK SDIO
8.3 Feature Description
8.3.1 Programmable Gain Amplifier
The LMP91050 offers two programmable gain modes (low or high) with four programmable gain settings each.
The purpose of the gain mode is to enable thermopiles with larger dark voltage levels. All gain settings are
accessible through bits GAIN1 and GAIN2[1:0]. The low-gain mode has a range of 167 V/V to 1335 V/V while the
high-gain mode has a range of 1002 V/V to 7986 V/V. The PGA is referenced to the internally generated VCM.
Input signal, referenced to this VCM voltage, should be within ±2 mV (see VINMAX_HGM specification) in highgain mode. In the low gain mode the first stage will provide a gain of 42 V/V instead of 250 V/V, thus allowing a
larger maximum input signal up to ±12 mV (VINMAX_LGM).
Table 1. Gain Modes
BIT SYMBOL
0: 250 (default)
GAIN1
12
GAIN
1: 42
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Feature Description (continued)
Table 1. Gain Modes (continued)
BIT SYMBOL
GAIN
00: 4 (default)
01: 8
GAIN2 [1:0]
10: 16
11: 32
8.3.2 External Filter
The LMP91050 offers two different measurement modes selectable through EXT_FILT bit. EXT_FILT bit is
present in the Device configuration register and is programmable through SPI.
Table 2. Measurement Modes
BIT SYMBOL
EXT_FILT
MEASUREMENT MODE
0: The signal from the thermopile is being processed by the internal PGAs, without
additional external decoupling or filtering (default).
1: The signal from the thermopile is being processed by the first internal PGA and fed to the A0
pin. An external low pass, high pass or band pass filter can be connected through pins A0, A1.
An external filter can be applied when EXT_FILT = 1. A typical band pass filter is shown in the picture below.
Resistor and capacitor can be connected to the CMOUT pin of the LMP91050 as shown. Discrete component
values have been added for reference.
10 µF
160 k
A1
A0
6.8 nF
160 k
CMOUT
Figure 21. Typical Bandpass Filter
8.3.3 Offset Adjust
Procedure of the offset adjust is to first measure the dark signal, program the DAC to adjust, and then measure
in a second cycle the residual of the dark signal for further signal manipulation within the µC. The signal source
is expected to have an offset component (dark signal) larger than the actual signal. During the dark phase, the
time when no light is detected by the sensor, the µC can program LMP91050 internal DAC to compensate for a
measured offset. A low output offset voltage temperature drift (TCVOS) ensures system accuracy over
temperature. See Figure 22 below which plots the maximum TCVOS allowed over a given temperature drift in
order to achieve n bit system accuracy.
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MAX TCVOS (mV/°C)
100
12 bit Accuracy
11 bit Accuracy
10 bit Accuracy
9 bit Accuracy
8 bit Accuracy
10
1
100m
10m
1
2 3 4 5 6 7 8 9
TEMPERATURE DRIFT (°C)
10
Figure 22. System Accuracy vs. TCVOS and Temperature Drift
8.3.4 Common-Mode Generation
As the offset of the sensor is bipolar, there is a need to supply a VCM to the sensor. This can be programmed as
1.15 V or 2.59 V (approximately mid rail of 3.3-V or 5-V supply). TI does not recommend to use 2.59-V VCM with
a 3.3-V supply
8.3.5 CSB
Chip Select is a active-low signal. CSB needs to be asserted throughout a transaction. That is, CSB should not
pulse between the Instruction Byte and the Data Byte of a single transaction.
NOTE
CSB de-assertion always terminates an on-going transaction, if it is not already complete.
Likewise, CSB assertion will always bring the device into a state, ready for next
transaction, regardless of the termination status of a previous transaction.
CSB may be permanently tied low for a 2-wire SPI communication protocol.
8.3.5.1 SCLK
SCLK can idle High or Low for a write transaction. However, for a READ transaction, SCLK must idle high. SCLK
features a Schmitt-triggered input and although it has hysterisis, TI recommends to keep SCLK as clean as
possible to prevent glitches from inadvertently spoiling the SPI frame.
8.4 Device Functional Modes
To read the registers of the LMP91050, the SDIO mode enable register must be written using a special
sequence, as described in the SDIO Mode section. During the reading process, the analog OUT pin is still active,
as normal. There are no other special modes for the device.
8.5 Programming
8.5.1 SPI Interface
An SPI interface is available in order to program the device parameters like PGA gain of two stages, enabling
external filter, enabling power for PGAs, offset adjust and common-mode (VCM) voltage.
8.5.1.1 Interface Pins
The Serial Interface consists of SDIO (Serial Data Input / Output), SCLK (Serial Interface Clock) and CSB (Chip
Select Bar). The serial interface is write-only by default. Read operations are supported after unlocking the
SDIO_MODE_PASSWD. This is discussed in detail later in the document.
14
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Programming (continued)
8.5.1.2 Communication Protocol
Communication on the SPI normally involves Write and Read transactions. Write transaction consists of single
Write Command Byte, followed by single Data byte. The following figure shows the SPI Interface Protocol for
write transaction.
CSB
1
2
3
4
5
6
7
8
9
11
10
12
13
14
15
16
SCK
COMMAND FIELD
DATA FIELD
MSB
c7
Wb=0
c6
c5
c4
c3
Reserved to 0
c2
c1
c0
d7
LSB
d6
d5
Address (4 bits)
d4
d3
d2
d1
d0
Write Data (8-bits)
Figure 23. SPI Interface Protocol
For Read transactions, user first needs to write into a SDIO mode enable register for enabling the SPI read
mode. Once the device is enabled for Reading, the data is driven out on the SDIO pin during the Data field of the
Read Transaction. SDIO pin is designed as a bidirectional pin for this purpose. Figure 24 shows the Read
transaction. The sequence of commands that need to be issued by the SPI Master to enable SPI read mode is
shown in Figure 25.
Figure 24. Read Transaction
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Programming (continued)
Sequence of transactions for unlocking SDIO_MODE
CSB
SDI
Write cmd
(sdio_mod
e_en reg)
Write data Write cmd Write
(0xFE first (sdio_mode data
byte of
_en reg) (0xED)
sdio_mode
_en reg)
Read cmd (to
read contents of
any register
specified by the
address bits)
SDO
Read data
Bus turnaround time = half cycle
Note:
1. Once the SDIO_mode is unlocked. The user can read as many registers as long as nothing
else is written to sdio_mode_en register to disturb the state of SDIO_mode
2. The separate signals SDI and SDO are given in the figure for the sake of understanding.
However, only one signal SDIO exists in the design
Figure 25. Enable SDIO Mode for Reading SPI Registers
8.5.1.3 Registers Organization
Configuring the device is achieved using Write of the designated registers in the device. All the registers are
organized into individually addressable byte-long registers that have a unique address. The format of the Write/
Read instruction is as shown below.
Table 3. Write / Read Instruction Format
Bit[7]
0 : Write Instruction
1 : Read Instruction
Bit[6:4]
Reserved to 0
Bit[3:0]
Address
8.6 Register Maps
This section describes the programmable registers and the associated programming sequence, if any, for the
device. Table 4 shows the summary listing of all the registers that are available to the user and their power-up
values.
Table 4. Register Descriptions
Title
Address (Hex)
Device Configuration
0x0
DAC Configuration
0x1
SDIO Mode Enable
0xF
16
Power-up/Reset
Value (Hex)
Type
Read-Write
(Read allowed in SDIO Mode)
Read-Write
(Read allowed in SDIO Mode)
Write-only
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0x0
0x80
0x0
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8.6.1 Device Configuration
Table 5. Device Configuration Register (Address 0x0)
Bit
Bit Symbol
7
RESERVED
Description
Reserved to 0.
00: PGA1 OFF PGA2 OFF (default)
[6:5]
EN
01: PGA1 OFF, PGA2 ON
10: PGA1 ON, PGA2 OFF
11: PGA1 ON, PGA2 ON
4
EXT_FILT
3
CMN_MODE
0: PGA1 to PGA2 direct (default)
1: PGA1 to PGA2 via external filter
0 : 1.15V (default)
1 : 2.59V
00: 4 (default)
[2:1]
GAIN2
01: 8
10: 16
11: 32
0
GAIN1
0: 250 (default)
1: 42
8.6.2 DAC Configuration
The output DC level will shift according to the formula Vout_shift = -33.8mV * (NDAC - 128).
Table 6. DAC Configuration Register (Address 0x1)
Bit
Bit Symbol
[7:0]
NDAC
Description
128 (0x80): Vout_shift = -33.8mV * (128 - 128) = 0mV (default)
8.6.3 SDIO Mode
Write-only
Table 7. SDIO Mode Enable Register (Address 0xf)
Bit
[7:0]
Bit Symbol
SDIO_MODE_EN
Description
To enter SDIO Mode, write the successive sequence 0xFE and 0xED.
Write anything other than this sequence to get out of mode.
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9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
Figure 26 shows a typical NDIR sensing circuit with a bandpass filter with a high frequency cutoff of
approximately 100 Hz. The lowpass filter at the output has a cutoff of approximately 110 Hz.
9.2 Typical Application
10 µF
6.8 nF
160 k
VDD
10 µF
CMOUT
10 nF
VDD
Thermopile
160 k
A0
A1
OUT
IN
1 kO
û ADC
10 nF
LMP91050
1 µF
CSB
CMOUT
SCLK
SDIO
10 nF
GND
Figure 26. Typical NDIR Sensing Application Circuit
9.2.1 Design Requirements
The design requirements for using the LMP91050 in an application basically include the following:
• Determine the characteristics of the thermopile and the appropriate gain and common mode voltage that will
maximize the dynamic range of the sensor. Consult the manufacturer’s data sheet.
• Selecting an analog-to-digital converter that supports the needed resolution and update rate.
• Determining the bandwidth of the inter-stage low-pass filter to limit the noise imposed on the signal
• An SPI interface to a microcontroller or other logic device is required in order to configure the LMP91050.
9.2.2 Detailed Design Procedure
The basic design procedure is as follows:
• Select the appropriate inter-stage bandpass filter bandwidth. Note that the common mode voltage (CMOUT)
is connected to both the thermopile and the bandpass filter, as shown in Figure 26.
• TI recommends that a lowpass filter be inserted between the OUT pin and the input to the ADC, to further
reduce noise on the signal and prevent aliasing.
• Power supply bypassing as shown in figure 32 is recommended.
• Based on the thermopile characteristics, select the common-mode voltage and gain to be programmed into
the LMP91050. CMOUT should be selected to center the expected dynamic range of the thermopile within
the full scale range of the ADC to the best extent possible. The gain should be selected to maximize the
18
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Typical Application (continued)
•
signal range at the ADC input, but should allow some headroom below full scale to prevent clipping. The gain
should also compensate, if possible, for any loss due to the filters in the signal path.
The internal DAC can be programmed to further optimize the signal range on the OUT pin. See Offset Adjust
for further information.
9.2.3 Application Curves
60
40
G = 32 V/V
G = 16 V/V
G = 8 V/V
G = 4 V/V
G = 250 V/V
G = 42 V/V
50
GAIN (dB)
GAIN (dB)
30
40
30
20
20
10
10
0
0
1k
10k
100k
FREQUENCY (Hz)
1M
10k
Figure 27. PGA1 Small Signal Bandwidth
140
G = 7986 V/V
G = 4003 V/V
G = 2004 V/V
G = 1002 V/V
NOISE DENSITY (nV/¥+])
PSRR (dB)
10M
Figure 28. PGA2 Small Signal Bandwidth
120
110
100k
1M
FREQUENCY (Hz)
100
90
80
70
120
100
60
80
60
40
20
0
10
100
FREQUENCY (Hz)
1k
Figure 29. Power Supply Rejection Ratio vs. Frequency
100m
1
10
100
1k
FREQUENCY (Hz)
10k
Figure 30. Input-Referred Noise Density vs. Frequency
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Typical Application (continued)
3.5
5.50
G = 1002 V/V
G = 2004 V/V
G = 4003 V/V
G = 7986 V/V
2.5
2.0
1.5
VDD = 3.3V
1.0
0.5
0.0
4.00
3.25
2.50
VDD = 5V
1.75
1.00
0.25
-0.5
-0.50
0
50
100 150 200
DAC CODE
250
300
Figure 31. DAC DC Sweep With VDD = 3.3 V
20
G = 1002 V/V
G = 2004 V/V
G = 4003 V/V
G = 7986 V/V
4.75
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.0
0
50
100 150 200
DAC CODE
250
300
Figure 32. DAC DC Sweep With VDD = 5 V
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10 Power Supply Recommendations
Because the LMP91050 is used in a sampled data system, care must be taken to maintain power supply noise
below an acceptable level, which will depend on the requirements of the application. In all cases, follow the
manufacturer’s design recommendations for the power conditioning device used in the system. The LMP91050
offers excellent power supply rejection over a wide range of frequencies, but adequate power supply bypassing
should always be used (see Figure 26). If using a switching supply, additional filtering may be required
particularly if the switcher harmonics fall within the passband of the filters used in the system. Ensure that the
selected power conditioning device is capable of sourcing the current required by the LMP91050.
11 Layout
11.1 Layout Guidelines
Figure 33 shows a layout example for the LMP91050. All components should be placed as close as possible
to the device, especially the bypass capacitors to VDD (CBypass1 and CBypass2).
11.2 Layout Example
Figure 33. LMP91050 Layout Example
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12 Device and Documentation Support
12.1 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.2 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
12.3 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.4 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LMP91050MM/NOPB
ACTIVE
VSSOP
DGS
10
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
AN8A
LMP91050MME/NOPB
ACTIVE
VSSOP
DGS
10
250
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
AN8A
LMP91050MMX/NOPB
ACTIVE
VSSOP
DGS
10
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 105
AN8A
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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