Universal Sensors and Transducers
Interface
USTI
FEATURES
29 measuring modes and one generator mode
2 identical channels
Provides frequency (time)-to-digital conversion
for many types of sensors and transducers
Provides interfacing for resistive (including
platinum (Pt), cuprum (Cu) resistors and
thermistors (Ni)), capacitive sensing elements
and resistive bridges
Frequency range from 0.05 Hz up to 9 MHz
without prescaling and 144 MHz with
prescaling;
Programmable accuracy (relative error) for
frequency (period) conversion from 1 % to
0.0005%
Relative quantization error is constant in all
specified frequency range
Non-redundant conversion time
Scalable resolution
Internal reference clock 625 kHz, 20 MHz
@ 20 MHz quartz oscillator
Quartz-accurate automated calibration
3-wire serial interface (SPI compatible)
2-wire interface (I
2
C compatible)
RS-232/485 serial interface
Master and slave communication modes
Frequency generator mode 10 MHz with quartz
crystal stability
FUNCTIONAL BLOCK DIAGRAM
resolution and programmable accuracy during the non-
redundant conversion time.
The USTI covers a wide range of frequencies and
accuracies for modern frequency-time domain
sensors. In addition, the USTI provides interfacing for
resistive (including platinum, cuprum resistors and
thermistors), capacitive sensing elements and resistive
bridges.
By using this IC it is possible to build a wide variety of
digital, smart sensors and intelligent sensor systems.
The device represents a high-resolution conversion
and designed to support all range of frequency-time
domain and digital sensor applications. It offers high
performances with flexibility and requires minimum
possible number of external components.
The USTI can be easy included into digital
environment, controlled by an external microcontroller
(slave mode) or work independently as a separate
measuring unit without an external control (master
mode). The function selection can be configured in
both software and hardware.
The IC converts frequency-time domain signals,
resistance and capacitance of sensing elements and
resistance of sensor bridges into digital and provides
digital, bus interface to microcontroller, DAQ or sensor
system to read these digital results. Sensing elements
can be directly connected to the USTI without the need
for extra electronics. Only a single reference element,
of the same kind as the sensor, is required.
The USTI has 29 measuring and one generating
modes. The measuring mode can be hardware-
APPLICATIONS
Physical and Chemical Sensor Systems
Digital Sensors, SoC, SiP, BioMEMS, Lab-on-Chip
Smart and Intelligent Sensors and Systems
Industrial and Process Control
Data Acquisition Systems
Instrumentations
Customer Electronics
Automotive
GENERAL DESCRIPTION
The Universal Sensors and Transducers Interface
(USTI) is a fully digital CMOS integrated circuit of
universal, 2-channel, high precision, multifunctional
converter based on novel, advanced methods for
frequency, period, its ratio, duty-cycle and phase-shift
measurements. It is perfectly suited to any applications
where frequency-time parameters but also sensors
output signal, have to be measured with highest
selected by using four selection external pins M0-M2
and the relative error by using four selection pins N0-
N2 (RS232 master communication mode). The mode
and accuracy can be also selected by using any of
three possible interfaces (slave communication mode).
A communication interface type (RS232, SPI or I
2
C)
can be automatically selected according to the circuit
connection.
according to the following equation:
q
½
1
100%,
20
10
6
t
x
where
t
x
is the appropriate measuring value of
t
p
, t
s
or
x
depending on the mode.
MEASURING MODES
Frequency, f
x
0.05 Hz – 9 MHz directly and up to
144 MHz with prescaling
Period, T
X
110 ns – 20 s
Phase shift,
X
0 - 360º at f
xmax
= 625 kHz
at 50 % duty-cycle
Time interval between start – and stop-pulse,
X
1.5 µs – 250 s
Duty-cycle, DC 0 – 1 at f
xmax
≤
625 kHz
Duty-off factor, Q
1
10
-8
– 8·10
6
at f
xmax
≤
625 kHz
Frequency difference, f
X2
– f
X2
with sign recognition,
0 – 9 MHz
Period difference, T
X1
– T
X2
with sign recognition,
0 – 20 s
Frequency ratio, f
X1
/f
X2
5.5·10
-9
– 1.8·10
8
Period ratio, T
X1
/T
X2
4.0·10
-9
– 2·10
8
Rotation speed, n
X
= (f
X
·60)/Z, where Z
is the number of encoder teeth
Pulse width, t
P
1.5 µs – 250 s
Space interval, t
S
1.5 µs – 250 s
Pulse number (events) counting, N
X
0 – 4·10
9
Frequency deviation absolute D
A1,
0-9 MHz
Frequency deviation relative D
R1,
0-100 %
Resistance, R
x
10
to 10 M with average relative
error
0.47
% and
0.01
% error at splitting of the
range into sub ranges
Capacitance, C
x
50 pF to 100
F
with average
relative error
0.036
% and
0.7
% the worst case
relative error
Resistive bridges, B
x
must not include any internal
components other than 4 arms forming a bridge
NOTE: The USTI can also work with any voltage and
current output sensors. It this case, any voltage–to-
frequency converter (VFC) can be used. The accuracy
of such system will be determined by sensor accuracy
as well as by VFC accuracy.
COMMUNICATION MODES
The USTI can work as an independent measuring unit
(master mode), controlled by any external
microcontroller (or embedded into a sensor), DAQ
board or PC (slave mode). In the master mode, the
conversion accuracy and measurement mode should
be selected by external switches. In this mode the
USTI works only through the RS232 interface in a
unidirectional mode. In the slave mode (with an
external microcontroller), all measuring modes and
programmed accuracy can be set up by a data bus or
through communication I/O ports of master
microcontroller. This allows us use the USTI as a
simple peripheral circuit for a microcontroller. A
bidirectional data exchange is possible with any of
three interfaces RS232, SPI or I
2
C. The USTI works as
a standard element in different systems with I
2
C bus
architecture, or can be controlled through the RS232
or SPI interfaces. The choice of interface can be
performed automatically depend on the circuit
connections.
The selection of communication interface is performed
automatically based on the state of IS1 and IS2 inputs
at the power switch on:
IS1
0
0
1
1
IS2
0
1
0
1
Communication Interface
SPI slave
I2C slave
RS232 master
RS232 slave
CHARACTERISTICS
Single power supply, V: 4.5 – 5.5
External reference frequency, MHz: 20
Internal reference frequency, kHz: 625
Conversion time, s: 0.00016 to 0.32
Supply current (at 20 MHz, 4.5V, 25ºC), mA: < 9.5
Operating temperature range -40ºC to +85ºC
Storage temperature range -65°C to +150°C
ACCURACY
The USTI has programmable relative error from 1 to
0.0005 % in all specified range of frequencies for
frequency and period measurements. This error is
constant and does not depend on the measuring
frequencies in all frequency ranges. The USTI has
non-redundant conversion time. The higher conversion
accuracy needs longer conversion time. However, it is
non-redundant for any selected accuracy and
frequency. For time interval, phase shift, pulse width
and space measurements the relative error is
determined mainly by measurnd and can be calculated
PIN-OUT AND HOUSING
The USTI is available in a 28-lead (0.300"/7.62 mm
Wide) Plastic Dual Inline Package (PDIP); 32-lead 7 x
7 mm Body Size, 1.0 mm Body Thickness, 0.8 mm
Lead Pitch small Thin Profile Plastic Quad Flat
Package (TQFP); and 32-pad, 5 x 5 x 1.0 mm Body,
2
Lead Pitch 0.50 mm, 3.10 mm Exposed Pad, Micro
Lead Frame Package (MLF).
TQFP/MLF TOP VIEW
PIN FUNCTION DESCRIPTIONS
Name
VCC
GND
FX1, ST1
FX2, ST2
OSC1, OSC2
M0, M1, M2
N0, N1, N2
A0, A1, A2
TEST
SCK
MISO
MOSI
SS
SCL
SDA
RXD
TXD
IS0,IS1
BN
BW
BS
CE1
CE2
CHRG, MES,
SMPL
Pin Descriptions
Supply voltage
Ground
Input channel 1
Input channel 2
Oscillator
Mode selection (see table)
Accuracy selection (see table)
Address of I
2
C slave (for I
2
C bus
communication)
Calibration signal
SPI Bus Master clock Input
SPI Bus Master Input/Slave Output
SPI Bus Master Output/Slave Input
SPI Bus Master Slave select
Two-wire (I
2
C compatible) Serial Bus
Clock Line
Two-wire (I
2
C compatible) Serial Bus
Data Input/Output Line
UART Input
UART Output
Interface mode selection
North port of bridge
West port of bridge
South port of bridge
Calibration element 1
Calibration element 2
R
x
and C
x
measurement pins
FX2
ST1
GND
VCC
GND
VCC
OSC1
OSC2
1
2
3
4
5
6
7
8
24
23
22
21
20
19
18
17
M0/A0
MES/BS
NC
GND
NC
NC
VCC
SCK/N2
NOTE: Bottom Pad for MLF Package Should be
Soldered to Ground.
This device can also be supplied in wafer form. Please
contact Technology Assistance BCNA 2010 S. L. sales
office for detailed ordering information and minimum
quantities.
PDIP
For more detailed information, specifications and
application notes the following document are strongly
recommended:
Universal Sensors and Transducers
Interface (USTI): Specification and Application Note
NC
RXD
TXD/IS1
FX1
FX2
ST1
VCC
GND
OSC1
OSC2
ST2
CE2/BN
SMPL
CHRG
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
SCL
SDA/IS0
M2/A2
M1/A1
M0/A0
MES/BS
GND
NC
VCC
SCK/N2
MISO/N1
MOSI/N0
SS/TEST
CE1/BW
Technology Assistance BCNA 2010, S. L.
Riera de Tena, No. 9 Local 4, 08014,
Barcelona, Spain
Tel.:+34 680 282 682
E-mail: info@techassist2010.com
Web: http://www. techassist2010.com
3
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