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ZMD31050 RB

series

Advanced Differential Sensor Signal Conditioner

Datasheet

PRELIMINARY

Features

· Digital compensation of sensor offset, sensitivity,

temperature drift and non-linearity

· Accommodates nearly all bridge sensors by PGA

and programmable ADC

· Capable with sensor signals from 1 up to

275mV/V span

· Sensor connections check and aging detection
· Selectable temperature compensation reference:

bridge, thermistor, internal diode or external diode

· Output options: voltage (0...5V), current

(4...20mA), PWM, I

C, SPI, ZACwire

(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
· Operation temperature -40...+125°C

(-50...+150°C derated)

· Supply voltage +2.7V...+5.5V
· Available in SSOP16 or as die

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)

Brief Description

The ZMD31050 is a CMOS integrated circuit that
belongs to ZMD's RB

series. It performs highly-

accurate amplification/scaling and sensor-specific
correction of bridge sensor signals.
Digital compensation of sensor offset, sensitivity,
temperature drift and non-linearity is accomplished via
a 16-bit RISC micro-controller running a correction
algorithm with calibration 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

) can be used for a simple PC-controlled

calibration, 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

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

2/23

ZMD31050 RB

series

Advanced Differential Sensor Signal Conditioner

Datasheet

PRELIMINARY

Contents

CIRCUIT DESCRIPTION ..............................................................................................................3

1.1

IGNAL

LOW

..............................................................................................................................3

1.2

PPLICATION

ODES

...................................................................................................................4

1.3

NALOG

RONT

(AFE) .........................................................................................................5

1.3.1.

Programmable Gain Amplifier .............................................................................................5

1.3.2.

Measurement Cycle Realized by Multiplexer ......................................................................5

1.3.3.

Analog Offset Compensation ..............................................................................................6

1.3.4.

Analog-to-Digital Converter .................................................................................................6

1.4

YSTEM

ONTROL

.......................................................................................................................8

1.5

UTPUT

TAGE

...........................................................................................................................9

1.5.1.

Serial Digital Interface .......................................................................................................10

1.5.2.

ZACwire

Single Wire Digital Interface............................................................................10

1.5.3.

Analog Output ...................................................................................................................12

1.5.4.

Comparator Module (ALARM Output) ...............................................................................13

1.6

OLTAGE

EGULATOR

...............................................................................................................13

1.7

RROR

ETECTION

...................................................................................................................14

APPLICATION CIRCUIT EXAMPLES........................................................................................15

ESD/LATCH-UP-PROTECTION.................................................................................................15

PIN CONFIGURATION AND PACKAGE ...................................................................................16

IC CHARACTERISTICS .............................................................................................................17

5.1

BSOLUTE

AXIMUM

ATINGS

...................................................................................................17

5.2

PERATING

ONDITIONS

OLTAGES RELATED TO

VSS) ........................................................17

5.3

UILD

HARACTERISTICS

.......................................................................................................18

5.3.8 Cycle Rate versus A/D-Resolution ........................................................................................19

5.3.9 PWM Frequency....................................................................................................................19

5.4

LECTRICAL

ARAMETERS

OLTAGES RELATED TO

VSS)......................................................20

5.5

NTERFACE

HARACTERISTICS

...................................................................................................21

TEST ...........................................................................................................................................22

RELIABILITY ..............................................................................................................................22

CUSTOMIZATION ......................................................................................................................22

RELATED DOCUMENTS ...........................................................................................................22

10.

ORDERING INFORMATION.......................................................................................................23

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ZMD31050 RB

series

Advanced Differential Sensor Signal Conditioner

Datasheet

PRELIMINARY

1. Circuit

Description

1.1 Signal

Flow

Fig.3: Block diagram of ZMD31050

PGA

programmable gain amplifier

MUX

multiplexer

ADC

analog-to-digital

converter

CMC

calibration

microcontroller

DAC

digital-to-analog

converter

FIO1

flexible I/O 1: analog out (voltage/current), PWM2,
ZACwire

(one-wire-interface)

FIO2

flexible I/O 2: PWM1, SPI data out, SPI slave select, Alarm1, Alarm2

SIF

serial interface: I2C data I/O, SPI data in, clock

PCOMP programmable

comparator

EEPROM

for calibration parameters and configuration

on-chip temperature sensor (pn-junction)

ROM

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).

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ZMD31050 RB

series

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

ZACwire

). 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:

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

Analog output

- Choice of output method (voltage value, current loop, PWM) for output register 1.
- Optional choice of additional 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.

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ZMD31050 RB

series

Advanced Differential Sensor Signal Conditioner

Datasheet

PRELIMINARY

1.3

Analog Front End (AFE)

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 table shows the adjustable gains and the processable sensor signal spans.

No.

PGA Gain

Max. span in mV/V

1 420

2 300

2.8

3 210

4 150

5.6

5 105

6 75

11.2

7 52.5

8 37.5

22.4

9 21.75

10 14

11 10

12 7

13 3

275

Table 1: Adjustable gains and processable sensor signal spans

1.3.2.

Measurement Cycle Realized by Multiplexer

The Multiplexer selects, depending on EEPROM settings, the following inputs in a certain sequence.

Pre-amplified bridge sensor signal

Bridge temperature signal measured by external diode

Bridge temperature signal measured by internal pn-junction

Bridge temperature signal measured by bridge resistors

Separate temperature signal measured by external thermistor

Internal offset of the input channel measured by input short circuiting

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: ZMD31050AC

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: ZMD31050AC