ZMD31050
Advanced Differential Sensor Signal Conditioner
Datasheet
Features
•
•
•
•
•
•
•
•
•
•
•
•
Digital compensation of sensor offset, sensitivity,
temperature drift and non-linearity
Accommodates nearly all bridge sensors types
(signal spans from 1 up to 275mV/V processable)
Digital one-shot calibration: quick and precise
Selectable temperature compensation reference:
bridge, thermistor, internal diode or external diode
Output options: voltage (0...5V), current
(4...20mA), PWM, I
2
C, SPI, ZACwire
TM
(one-
wire-interface), alarm
Adjustable output resolution (up to 15 bits) versus
sampling rate (up to 3.9kHz)
Selectable bridge excitation: ratiometric voltage,
constant voltage or constant current
Input channel for separate temperature sensor
Sensor connection and common mode check
(Sensor aging detection)
operation temperature, depending on product
version, up to -40...+125°C (-55...+150°C
derated)
Supply voltage +2.7V...+5.5V
Available in SSOP16 or as die
PRELIMINARY
Brief Description
ZMD31050 is a CMOS integrated circuit for highly-
accurate amplification and sensor-specific correction
of bridge sensor signals. The device provides digital
compensation of sensor offset, sensitivity,
temperature drift and non-linearity by a 16-bit RISC
micro controller running a correction algorithm with
correction coefficients stored in non-volatile
EEPROM.
The ZMD31050 accommodates virtually any bridge
sensor (e.g. piezo-resistive, ceramic-thickfilm or steel
membrane based). In addition, the IC can interface a
separate temperature sensor.
The bi-directional digital interfaces (I C, SPI,
ZACwire
TM
) can be used for a simple PC-controlled
one-shot calibration procedure, in order to program a
set of calibration coefficients into an on-chip
EEPROM. Thus a specific sensor and a ZMD31050
are mated digitally: fast, precise and without the cost
overhead associated with laser trimming, or
mechanical potentiometer methods.
§
Application kit available (SSOP16 samples,
calibration PCB, calibration software, technical
documentation)
§
Support for industrial mass calibration
available
§
Quick circuit customization possible for large
production volumes
2
Benefits
•
•
•
No external trimming components required
PC-controlled configuration and calibration via
digital bus interface - simple, low cost
High accuracy (±0.1% FSO @ -25...85°C;
±0.25% FSO @ -40...125°C)
Application Circuit (Examples)
Fig.1: Ratiometric measurement with voltage output,
temperature compensation via external diode
Fig.2: Two wire 4...20mA (5...40V) configuration,
temperature compensation via internal diode
Copyright © 2004, ZMD AG, Rev. 0.7, 2004-09-02, PRELIMINARY
1/20
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written
consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
ZMD31050
Advanced Differential Sensor Signal Conditioner
Datasheet
PRELIMINARY
Contents
1.
CIRCUIT DESCRIPTION ............................................................................................................3
1.1 S
IGNAL
F
LOW
...........................................................................................................................3
1.2 A
PPLICATION
M
ODES
.................................................................................................................4
1.3 A
NALOG
F
RONT
E
ND
(AFE) .......................................................................................................5
1.3.1.
Programmable Gain Amplifier ........................................................................................5
1.3.2.
Analogue Sensor Offset Compensation - Extended Zero Shift (XZC)............................5
1.3.3.
Measurement Cycle Realized by Multiplexer .................................................................6
1.3.4.
Analog-to-Digital Converter............................................................................................7
1.4 S
YSTEM
C
ONTROL
....................................................................................................................8
1.5 O
UTPUT
S
TAGE
.........................................................................................................................9
1.5.1.
Analog Output..............................................................................................................10
1.5.2.
Comparator Module (ALARM Output)..........................................................................10
1.5.3.
Serial Digital Interface..................................................................................................10
1.6 V
OLTAGE
R
EGULATOR
.............................................................................................................11
1.7 E
RROR
D
ETECTION
.................................................................................................................11
2.
3.
4.
5.
APPLICATION CIRCUIT EXAMPLES ......................................................................................13
ESD/LATCH-UP-PROTECTION ...............................................................................................13
PIN CONFIGURATION AND PACKAGE...................................................................................14
IC CHARACTERISTICS............................................................................................................15
5.1 A
BSOLUTE
M
AXIMUM
R
ATINGS
.................................................................................................15
5.2 O
PERATING
C
ONDITIONS
(V
OLTAGES RELATED TO
VSS) ......................................................15
5.3 B
UILD
I
N
C
HARACTERISTICS
.....................................................................................................16
5.3.8 Cycle Rate versus A/D-Resolution ......................................................................................17
5.3.9 PWM Frequency .................................................................................................................17
5.4 E
LECTRICAL
P
ARAMETERS
(V
OLTAGES RELATED TO
VSS) ....................................................18
5.5 I
NTERFACE
C
HARACTERISTICS
.................................................................................................19
6.
7.
8.
9.
TEST ........................................................................................................................................20
RELIABILITY ............................................................................................................................20
CUSTOMIZATION ....................................................................................................................20
RELATED DOCUMENTS .........................................................................................................20
Copyright © 2004, ZMD AG, Rev. 0.7, 2004-09-02, PRELIMINARY
2/20
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written
consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
ZMD31050
Advanced Differential Sensor Signal Conditioner
Datasheet
PRELIMINARY
1.
1.1
Circuit Description
Signal Flow
Fig.3: Block diagram of ZMD31050
PGA
MUX
ADC
CMC
DAC
FIO1
FIO2
SIF
PCOMP
EEPROM
TS
ROM
PWM
programmable gain amplifier
multiplexer
analog-to-digital converter
calibration microcontroller
digital-to-analog converter
flexible I/O 1: analog out (voltage/current), PWM2,
ZACwire
TM
(one-wire-interface)
flexible I/O 2: PWM1, SPI data out, SPI slave select, Alarm1, Alarm2
serial interface: I2C data I/O, SPI data in, clock
programmable comparator
for calibration parameters and configuration
on-chip temperature sensor (pn-junction)
for correction formula and –algorithm
PWM module
The ZMD31050’s signal path is partly analog (blue) and partly digital (red).
The differential signal from the bridge sensor is pre-amplified by the programmable gain amplifier
(PGA). The Multiplexer (MUX) transmits the signals from bridge sensor, external diode or separate
temperature sensor to the ADC in a certain sequence (instead of the temp. diode the internal pn-
junction (TS) can be used optionally). Afterwards the ADC converts these signals into digital values.
The digital signal correction takes place in the calibration micro-controller (CMC). It is based on a
special correction formula located in the ROM and on sensor-specific coefficients (stored into the
EEPROM during calibration).
Copyright © 2004, ZMD AG, Rev. 0.7, 2004-09-02, PRELIMINARY
3/20
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written
consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
ZMD31050
Advanced Differential Sensor Signal Conditioner
Datasheet
PRELIMINARY
Dependent on the programmed output configuration the corrected sensor signal is output as analog
value, as PWM signal or in digital format (SPI, I
2
C,
ZACwire
TM
). The output signal is provided at 2
flexible I/O modules (FIO) and at the serial interface (SIF). The configuration data and the correction
parameters can be programmed into the EEPROM via the digital interfaces.
The modular circuit concept enables fast custom designs varying these blocks and, as a result,
functionality and die size.
1.2
Application Modes
For each application a configuration set has to be established (generally prior to calibration) by
programming the on-chip EEPROM regarding to the following modes:
§
−
−
−
−
−
§
−
−
−
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Sensor channel
Sensor mode: ratiometric voltage or current supply mode.
Input range: The gain of the analog front end has to be chosen with respect to the maximum
sensor signal span and the zero point of the ADC has to be set with respect to the possible input
voltage range
Additional offset compensation: The extended analog offset compensation has to be enabled if
required, e.g. if the sensor offset voltage is near to or larger than the sensor span.
Resolution/response time: The A/D converter has to be configured for resolution and converting
scheme (first or second order). These settings influence the sampling rate, signal integration time
and this way the noise immunity
Sample order: The order and interval of multiplexed measurements (pressure, temperature, auto
zero) has to be set
Ability to invert the sensor bridge inputs
Analog output
Choice of output method (voltage value, current loop, PWM) for output register 1.
Optional choice of output register 2: PWM module via IO1 or alarm out module via IO1/2.
Digital communication: The preferred protocol and its parameter have to be set.
Temperature
The temperature measure channel for the temperature correction has to be chosen.
Optional: the temperature measure channel as the second output has to be chosen.
Supply voltage : For non-ratiometric output the voltage regulation has to be configured.
§
§
§
Note:
Not all possible combinations of settings are allowed (see section 1.5).
The calibration procedure must include
−
the set of coefficients of calibration calculation
and depending on configuration,
−
the adjustment of the extended offset compensation,
−
the zero compensation of temperature measurement,
−
the adjustment of the bridge current
and if necessary
−
the set of thresholds and delays for the alarms,
−
the reference voltage.
Copyright © 2004, ZMD AG, Rev. 0.7, 2004-09-02, PRELIMINARY
4/20
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written
consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
ZMD31050
Advanced Differential Sensor Signal Conditioner
Datasheet
1.3
Analog Front End (AFE)
PRELIMINARY
The analog front end consists of the programmable gain amplifier (PGA), the multiplexer (MUX) and
the analog-to-digital converter (ADC).
1.3.1.
Programmable Gain Amplifier
The following tables show the adjustable gains, the processable sensor signal spans and the allowed
common mode range.
Max. span
Input range
in mV/V
in % VDDA
1
420
2
43 - 57
2
280
3
38 - 62
3
210
4
43 - 57
4
140
6
40 - 59
5
105
8
38 - 62
6
70
12
40 - 59
7
52,5
16
38 - 62
8
35
24
40 - 59
9
26,3
32
38 - 62
10
14
50
43 - 57
11
9,3
80
40 - 59
12
7
100
38 - 62
13
2,8
280
21 - 76
Table 1: Adjustable gains, resulting sensor signal spans and common mode ranges
1.3.2.
Analogue Sensor Offset Compensation - Extended Zero Shift (XZC)
No.
PGA Gain
The ZMD31050 supports two methods of sensor offset cancellation (zero shift):
•
•
digital offset correction
analogue cancellation for large offset values (up to 300% of span)
Digital sensor offset correction will be processed at the digital signal correction/conditioning by the
CMC. Analogue sensor offset precompensation will be needed for compensating of large offset
values, which would be overdrive the analogue signal path by uncompensated gaining. For analogue
sensor offset precompensation an compensation voltage will be added in the analogue pregaining
signal path (coarse offset removal). The analog offset compensation in the AFE can be adjusted by 6
EEPROM bits. It allows a zero point shift up to 300% of the processable signal span.
The zero point shift of the temperature measurements can also be adjusted by 6 EEPROM bits.
Copyright © 2004, ZMD AG, Rev. 0.7, 2004-09-02, PRELIMINARY
5/20
All rights reserved. The material contained herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written
consent of the copyright owner. The Information furnished in this publication is preliminary and subject to changes without notice.
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