last update November 30, 2010 reference smtutin page 1/27 Features • Provides interfacing for many types of sensor elements: Capacitors, platinum resistors, thermistors, Resistive bridges and potentiometers • • • • • • • • • • • • • Measurement of multiple sensor elements Single 2.9 V - 5.5 V power supply, current consumption below 2.
last update November 30, 2010 reference smtutin page 2/27 couplers required in insulated systems. For information about insulated UTI applications, please see the relevant application notes in the support shop of our website. Continuous auto-calibration of offset and gain of the complete system is performed by using the three-signal technique. The low-frequency interference is removed by an advanced chopping technique.
last update November 30, 2010 reference smtutin page 3/27 3. Absolute Maximum Ratings Specified at TA=25° unless otherwise noted Absolute maximum ratings at 25 °C. Power supply voltage Power supply current (excluding connection to the sensor) Power dissipation Power dissipation at power down Output voltage 21 mW 7 µW -0.3 V to VDD+0.3 V Output driving current (A,F) Output impedance Input voltage ref. to VSS 8 mA 60 Ω -0.3 V to VDD+0.
last update November 30, 2010 reference smtutin page 4/27 4.1 Output The UTI outputs a microcontroller-compatible period-modulated signal and excitation signals to drive the sensing elements. Table 3 shows some output specifications of the UTI. Because all UTI data is present on one single digital output, only four wires are needed to make a versatile insulated front end. For information about insulated use of UTI please go to the relevant application notes in the support shop of our website.
last update November 30, 2010 reference smtutin page 5/27 The pin PD is used to set the power-down of the UTI. When PD = 0, the UTI is powered down and the output node is floating (high-impedance). This enables to connect several UTI outputs to a single output wire, provided that only a single UTI is selected (PD = 1). The pin CML is always connected to GND except in mode CMUX. In mode CMUX, the pin CML is used for the measurement-range selection.
last update November 30, 2010 reference smtutin page 6/27 5. Some theory about measuring sensor elements 5.1 About the three-signal technique and calibration The three-signal technique is a technique to eliminate the effects of unknown offset and unknown gain in a linear system. In order to apply this technique, in addition to the measurement of the sensor signal, two reference signals are required to be measured in an identical way.
last update November 30, 2010 reference smtutin page 7/27 As explained above in the theory of the three signal technique the internal input of the UTI has to be switched to three or more elements. During the first phase the internal offset of the linear system is measured (normally there are no external components connected to the corresponding pins). During the second phase the UTI measures the value of a reference element, by switching to the corresponding connecting pins.
last update November 30, 2010 reference smtutin page 8/27 5.3 Resolution The output signal of the UTI is digitized by the microcontroller. This sampling introduces quantization noise, which also limits the resolution. The quantization noise of any phase measurement, as given by the relative standard deviation σq, amounts to: σq = 1 ts 6 Tphase (2) where ts is the sampling time and Tphase the phase duration.
last update November 30, 2010 reference smtutin page 9/27 3.5E-03 3.0E-03 Nonlinearity 2.5E-03 2.0E-03 1.5E-03 1.0E-03 5.0E-04 0.0E+00 -5.0E-04 0.0E+00 2.0E+02 4.0E+02 6.0E+02 8.0E+02 1.0E+03 1.2E+03 Parasitic capacitance (pF) Figure 5. The nonlinearity versus the parasitic capacitance Cp The measurement range equals 0 -2 pF 5.5 Capacitive measurements with the UTI The way UTI measures capacitance values is special.
last update November 30, 2010 reference smtutin page 10/27 In figure 5 the relation between accuracy and parasitic cable capacitance Cp is depicted. From the graph it can be seen that the linearity is still 1.0E-3 in case of a cable capacitance of about 500 pF. When multiple capacitances are measured, each node (fi A, B, C,D,E,F) is activated for a certain time and after that the UTI switches on to the next node.
last update November 30, 2010 reference smtutin ! page 11/27 6 CAPACITIVE MODES (MODE 0 – 4) 6.1 Mode 0. C25: 5 capacitors 0-2pF In this mode, 5 capacitors in the range of 0 - 2 pF with one common electrode can be measured. In order to understand what this means in practical terms, please refer to the note in paragraph 5.5. The connection of capacitors is depicted in Fig 6. All measured capacitors should have a common receiver electrode, connected to node A.
last update November 30, 2010 reference smtutin ! page 12/27 6.2 Mode 1. C23: 3 capacitors 0-2pF In this mode, 3 capacitors in the range of 0 - 2 pF with one common electrode can be measured. In order to understand what this means in practical terms, please refer to the note in paragraph 5.5. The difference with mode C25 is that one cycle consists of only 3 phases. The connection of the capacitors is shown in Fig 6 where CEA and CFA are omitted now.
last update November 30, 2010 reference smtutin ! page 13/27 6.4 Mode 3. CMUX: X capacitors 0-2pF/0-12pF, external MUX In this mode, an arbitrary number of capacitors in the range of 0 - 2 pF (CML = 0) or the range of 0 - 12 pF (CML = 1) with a common electrode can be measured. The UTI does not perform a phase selection, so an external multiplexer should be used. Just for this application, Smartec developed a novel multiplexer MUX with nine outputs and four inputs.
last update November 30, 2010 reference smtutin ! page 14/27 6.5 Mode 4. C300: 3 capacitors, range up to 300pF In this mode, 3 capacitors in a variable range up to 300 pF with a common electrode can be measured. In order to understand what this means in practical terms, please refer to the note in paragraph 5.5. The connection of sensors and external resistors is depicted in Figure 8. These resistors set the voltage swing at the transmitting electrode of CiA. Vdd Figure 8.
last update November 30, 2010 reference smtutin ! page 15/27 7 RESISTIVE MODES (MODE 5 – 15) 7.1 Mode 5. Pt: 1 platinum resistor Pt100/ Pt1000, 4-wire In this mode, one platinum resistor and one reference resistor can be measured. The connection of the resistors to the UTI is depicted in Figure 9. Because of the use of force/sense wires, both resistors Rx and Rref are measured in a 4-wire setup, thereby completely eliminating the effect of lead resistances.
last update November 30, 2010 reference smtutin ! page 16/27 To calculate the ratio as in (1), we have to make different calculations for the 2-, 3- and 4 wire measurement: M 2 − ,4 − wire = M 3− wire = Tphase 3 − Tphase1 Tphase 2 − Tphase1 Tphase 3 − Tphase 4 Tphase 2 − Tphase1 = Rx Rref (3) R = x Rref The linearity is better than 13 bits provided that the amplitude of the voltages VAB and VCD is below 0.7 V for VDD = 5V. For VDD = 3.3 V, these voltages should be less than 0.4 V.
last update November 30, 2010 reference smtutin ! page 17/27 7.2 Mode 6. Ther: 1 thermistor, 4-wire In this mode, one thermistor and one reference resistor can be measured. The connection of the thermistor and the reference resistor is shown in Figure 10. The driving voltage VEF is a chopped voltage with an amplitude of VDD/12.5 (0.4 V at VDD = 5 V) and a DC value VDD/2. The ratio of the thermistor and the reference resistor is also given by (3).
last update November 30, 2010 reference smtutin ! page 18/27 7.3 Mode 7. Pt2: 2 or 3 platinum resistors In this mode, 2 or 3 platinum resistors can be measured. The connection of the resistors to the UTI is shown in Figure 11. The voltage VEF is the same as in the mode Pt. Rbias RREF Rx1 RX2 E Rbia E A RREF A B Rx1 C RX2 D Rx3 F B C D F - .- Figure 11.
last update November 30, 2010 reference smtutin ! page 19/27 7.4 Mode 8. Ther2: 2 or 3 thermistors In this mode, 2 or 3 thermistors can be measured. The connection is depicted in Figure 12. The number of phases is also 5, as listed in Table 15. The specifications listed in Table 14 also hold for this mode. With the connection shown in Figure 12(a), the effect of lead resistances can not be eliminated.
last update November 30, 2010 reference " !# ! smtutin page 20/27 8 RESITIVE BRIDGE MODES (MODE 9 – 14) 8.1 Mode 9. Ub2: resistive bridge, ref. is Vbridge, +/- 4% imbalance In this mode, a resistive bridge can be measured where the ratio of the bridge output voltage VCD and the bridge supply voltage VAB represents the physical signal. The measurement range of the bridge imbalance is +/-4% in this mode. The connection of the bridge to the UTI is shown in Figure 13.
last update November 30, 2010 reference " !# ! smtutin page 21/27 To find the bridge imbalance, the microcontroller calculates: M= 1 Tphase 3 − Tphase1 VCD = 32 Tphase 2 − Tphase1 V AB (4) The specifications are listed in Table 17 Parameter (VDD = 5 V) Typical value K2 56 s/V V0 0.54 V Bridge excitation AC Vdd excitation current (max E - F) Bridge resistance Bridge output Voltage 20 mA 250 -10k <+/- 0,2V Accuracy 11 bits (over =/- 0.2V) Offset <10 V Resolution (SF=0) <7 V Table 17.
last update November 30, 2010 reference " !# smtutin ! page 22/27 Parameter (VDD = 5 V) Typical value K2 56 s/V V0 0.54 V Bridge excitation AC Vdd excitation current (max E - F) 20 mA Bridge resistance 250 -10k Bridge output Voltage Accuracy Offset Resolution (SF=0) <+/- 12,5 mV 10 bits (over =/- 0.2V) <10 V < 700 nV Table 19.
last update November 30, 2010 reference " !# ! smtutin page 23/27 8.4 Mode 12. Ib1: resistive bridge, ref. is Ibridge,+/- 0.25% imbalance This mode is similar to mode 11. The connection of the bridge and the resistor is shown in Figure 14. The difference with mode 11 is that the bridge imbalance range is +/- 0.25%. The voltage across the reference resistor should be between 0.1 V and 0.2 V, as in mode 11.
last update November 30, 2010 reference " !# smtutin ! page 24/27 8.5 Mode 13. Brg2: resistive bridge +/- 4% and 2 resistors In this mode, a resistive bridge with a maximum imbalance of +/-4% and two resistors can be measured. One of the resistors can be temperature dependent, so the bridge output can be digitally corrected for temperature effects. Both the voltage across the bridge and the current through the bridge are measured. The connection of the elements to the UTI is shown in Figure 15.
last update November 30, 2010 reference " !# smtutin ! page 25/27 8.6 Mode 14. Brg1: resistive bridge +/- 0.25% and 2 resistors This mode is similar to mode 13. The connection is shown in Figure 15. The difference with mode 13 is that the measurement range of the bridge imbalance is 0.25%. The bridge output voltage VCD is amplified 15 times before it is processed further. The voltages measured during each phase are indicated in Table 26. The specifications are listed in Table 27.
last update November 30, 2010 reference " !# smtutin ! page 26/27 8.7 Mode 15. Potm: 3 potentiometers, 1kΩ Ω-25kΩ Ω In this mode, 3 potentiometers in the range of 1 kΩ to 50 kΩ can be measured. The connection of potentiometers is depicted in Figure 16. When only a single potentiometer is measured with its slide connected to, for instance, node B, nodes C and D should be connected to F.
last update November 30, 2010 reference smtutin ! page 27/27 9. Encapsulations " " ( " % &" % # $ 2 & $ &" 3,# # × ,# # % % " 1 $ , 4 0 61 0 %% !* ' +, -. 6, 6 45 63 *' ,, 5 && ) Figure 17 The pad configuration of UTI SOIC/die 10. Development Kit Fo0 actual development purposes, a development kit is available. This kit can be connected directly to a personal computer. Additional practical information can be found in the UTI application notes in the supports shop of our website.
