SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Description
The SX8725 is a data acquisition system based on
Semtech’s low power ZoomingADC™ technology. It
directly connects most types of miniature sensors
with a general purpose microcontroller.
With 1 differential input, it can adapt to multiple
sensor systems. Its digital outputs are used to bias
or reset the sensing elements.
Features
•
•
•
•
•
•
•
•
•
•
Up to 16-bit differential data acquisition
Programmable gain: (1/12 to 1000)
Sensor offset compensation up to 15 times
full scale of input signal
1 differential or 2 single-ended signal inputs
Programmable Resolution versus Speed
versus Supply current
2 digital outputs to bias Sensors
Internal or external voltage reference
Internal time base
Low-power (250 uA for 16b @ 500 S/s)
2-WIRE interface
Applications
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•
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Industrial pressure sensing
Industrial temperature sensing
Barometer
Compass
Ordering Information
Device
Package
Reel quantity
3000
1000
SX8725E083TRT
MLPD-W-12 4x4
SX8725E083TDT
MLPD-W-12 4x4
1) Available in tape and reel only
2) Lead free, WEEE and RoHS compliant.
Functional Block Diagram
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SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Table of Contents
Description..............................................................................................................................................................1
Applications............................................................................................................................................................1
Features ..................................................................................................................................................................1
Ordering Information .............................................................................................................................................1
Functional Block Diagram.....................................................................................................................................1
Absolute Maximum Ratings ..................................................................................................................................4
Electrical Characteristics ......................................................................................................................................5
ZoomingADC Specifications.................................................................................................................................6
Timing Characteristics ..........................................................................................................................................8
2-WIRE Timing Waveforms ...................................................................................................................................8
Pin Configuration ...................................................................................................................................................9
Marking Information...............................................................................................................................................9
Pin Description .......................................................................................................................................................9
Circuit Description ...............................................................................................................................................10
General Description .............................................................................................................................................. 10
Block Diagram ....................................................................................................................................................... 10
VREF ..................................................................................................................................................................... 10
GPIO ..................................................................................................................................................................... 11
Charge Pump ........................................................................................................................................................ 12
RC Oscillator ......................................................................................................................................................... 13
2-WIRE.................................................................................................................................................................. 14
2-WIRE Communication Format ........................................................................................................................... 14
2-WIRE Address.................................................................................................................................................... 14
ZoomingADC ........................................................................................................................................................15
Features ................................................................................................................................................................ 15
Overview ............................................................................................................................................................... 15
ZADC Description.................................................................................................................................................. 15
Acquisition Chain................................................................................................................................................... 15
Registers ............................................................................................................................................................... 17
ZADC Detailed Functionality Description .............................................................................................................. 18
Continuous-Time vs. On-Request......................................................................................................................... 18
Input Multiplexers .................................................................................................................................................. 19
Programmable Gain Amplifiers ............................................................................................................................. 20
PGA & ADC Enabling............................................................................................................................................ 21
PGA1 ..................................................................................................................................................................... 21
PGA2 ..................................................................................................................................................................... 21
PGA3 ..................................................................................................................................................................... 21
ADC Characteristics .............................................................................................................................................. 22
Conversion Sequence ........................................................................................................................................... 22
Over-Sampling Frequency .................................................................................................................................... 22
Over-Sampling Ratio ............................................................................................................................................. 23
Elementary Conversions ....................................................................................................................................... 23
Resolution ............................................................................................................................................................. 24
Conversion Time and Throughput......................................................................................................................... 25
Output Code Format ............................................................................................................................................. 26
Power Saving Modes ............................................................................................................................................ 27
Registers Map ....................................................................................................................................................... 28
Registers Descriptions .......................................................................................................................................... 28
RC Register........................................................................................................................................................... 28
GPIO Registers ..................................................................................................................................................... 29
ZADC Registers .................................................................................................................................................... 30
Mode Register ....................................................................................................................................................... 31
Optional Operating Modes: External Voltage Reference Option .......................................................................... 32
Application Hints..................................................................................................................................................33
Recommended Operation Mode and Registers Settings...................................................................................... 33
Operation Mode..................................................................................................................................................... 33
V1.8 © 2009 Semtech Corp.
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SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Registers Settings ................................................................................................................................................. 33
Schematic.............................................................................................................................................................. 34
Input Impedance.................................................................................................................................................... 35
Switched Capacitor Principle ................................................................................................................................ 36
PGA Settling or Input Channel Modifications ........................................................................................................ 37
PGA Gain & Offset, Linearity and Noise ............................................................................................................... 37
Frequency Response ............................................................................................................................................ 38
Power Reduction ................................................................................................................................................... 39
Recommended Design for Other 2-WIRE Devices Connection ........................................................................... 39
Typical Performance ............................................................................................................................................40
Linearity ................................................................................................................................................................. 40
Integral Non-Linearity............................................................................................................................................ 40
Differential Non-Linearity....................................................................................................................................... 43
Noise ..................................................................................................................................................................... 44
Gain Error and Offset Error ................................................................................................................................... 46
Power Consumption .............................................................................................................................................. 47
PCB Layout Considerations................................................................................................................................49
How to Evaluate....................................................................................................................................................49
Package Outline Drawing: MLPD-W-12 4x4.......................................................................................................50
Land Pattern Drawing: MLPD-W-12 4x4.............................................................................................................51
Tape and Reel Specification ...............................................................................................................................52
V1.8 © 2009 Semtech Corp.
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SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device or device malfunction.
Operation outside the parameters specified in the Electrical Characteristics section is not implied.
Parameter
Power supply
Storage temperature
Temperature under bias
Max sensor common mode
Input voltage
Peak reflow temperature
T
PKG
Notes:
This device is ESD sensitive. Use of standard ESD handling precautions is required.
Symbol
V
BATT
T
STORE
T
BIAS
V
VR_P
V
VR_N
Comments / Conditions
Min
V
SS
- 0.3
-55
-40
V
SS
- 300
V
SS
- 300
Max
5.7
150
140
V
BATT
+ 300
V
BATT
+ 300
260
Unit
V
°
C
°
C
mV
mV
°
C
V1.8 © 2009 Semtech Corp.
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SX8725
ZoomingADC™ for Pressure and Temperature Sensing
ADVANCED COMMUNICATIONS & SENSING
Electrical Characteristics
All values are valid within the operating conditions unless otherwise specified.
Parameter
Operating conditions
Power supply
Operating temperature
V
BATT
T
OP
2.4
-40
5.5
125
V
°C
Symbol
Comments / Conditions
Min
Typ
Max
Unit
Current consumption
Active current, @ 30 ° 5.5 V
C,
I
OP
16 b @ 250 Sample/s
ADC, f
s
= 125 kHz
16 b @ 1 kSample/s
PGA3 + ADC, f
s
= 500 kHz
16 b + gain 1000 @ 1 kSample/s
PGA3,2,1 + ADC, f
s
= 500kHz
Active current, @ 30 ° 3.3 V
C,
I
OP
16 b @ 250 Sample/s
PGA3 + ADC, f
s
= 125 kHz
16 b @ 1 kSample/s
PGA3 + ADC, f
s
= 500 kHz
16 b + gain 1000 @ 1 kSample/s
PGA3,2,1 + ADC, f
s
= 500kHz
Sleep current
I
sleep
@ 30 °
C
up to 85 °
C
@125 °
C
250
700
1000
150
300
850
75
100
150
200
nA
300
800
1200
µA
µA
Time base
Max ADC over-sampling frequency
Min ADC over-sampling frequency
F
Smax
F
Smin
@ 25 °
C
@ 25 °
C
450
56.25
500
62.5
550
68.75
kHz
kHz
Digital I/O
Input logic high
Input logic low
Output logic high
Output logic low
V
IH
V
IL
V
OH
V
OL
I
OH
< 4mA
I
OL
< 4mA
0.4
0.7
0.3
V
BATT
-0.4
V
BATT
V
BATT
V
V
VREF: Internal Bandgap Reference
Absolute output voltage
Variation over Temperature
Total Output Noise
V
BATT
> 3V
V
BATT
> 3V, ref to 25° C
V
BATT
> 3V, rms, broadband
1.19
-1
1.22
1.25
+1
1
V
%
mV
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