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Converter IC for Capacitive Signals
FEATURES
* Wide Supply Voltage Range: 5...18V * Wide Operating Temperature Range: -25C...+85C * High Detection Sensivity of Relative Capacitive Changes: 5% - 100% * Detection Frequency up to 2kHz * Adjustable Voltage Output * Adjustable Namur Current Output * Low Power Dissipation: 5mW @ 5V
CAN404
GENERAL DESCRIPTION
The CAN404 is a universal multipurpose interface for capacitive sensors and contains the complete signal conditioning unit on chip. The CAN404 detects the relative capacitive change of a measuring capacity to a fixed reference capacity. The IC is optimized for capacities in the wide range of 10pF to 2nF with possible changes of capacity of 5% to 100% of the reference capacity. The CAN404 offers an output signal proportional to the change of the measuring capacity and can be adjusted by an active lowpass filter. Referring the output signal to an internal reference allows a temperature compensation. In addition to the voltage output, a voltage-to-current interface according to the Namur norm is implemented. With only a few external components, the CAN404 is suitable for a great variety of applications including a zero compensation.
APPLICATIONS
* * * * * Industrial Process Control Distance Measurement Pressure Measurement Humidity Measurement Level Control
BLOCK DIAGRAM
COSC 16
Reference Oscillator fosc
VB+ 10
VBCX1 18 CX2 20
Capacitive Oscillator 1 Capacitive Oscillator 2
V I
GND
9
8 Imax
VSTAB R01
LOWPASS
R02
Internal Power Supply
19
VBG 15
CL1 1
RL1 2
RL2 3
CL2 4
RL3 5
LPOUT 6
SET 7
VM 17
RCX1
RCX2 14
ROSC RSUP 13 12 11
Figure 1
analog microelectronics
Analog Microelectronics Vertriebs GmbH & Co. KG An der Fahrt 13, D - 55124 Mainz Internet: http://www.analogmicro.de Phone: +49 (0)6131/91 073 - 0 Fax: +49 (0)6131/91 073 - 30 E-Mail: amv@analogmicro.de
March 99 1/6 Rev. 2.2
Converter IC for Capacitive Signals
ELECTRICAL SPECIFICATIONS
Tamb = 25C, VCC = 8.2V, RI = 1k (unless otherwise noted)
Parameter Supply Voltage Range Supply Current Range Symbol VCC ICC,0 ICC Temperature Specifications Operating Storage Junction Reference Voltage Reference Voltage 4.5V Temperature Coefficient VVSTAB Reference Voltage VBG Temperature Coefficient VBG Reference Voltage 2V Temperature Coefficient VM Reference Oscillator Oscillator Capacitor Oscillator Frequency Oscillator Current Capacitive Oscillators 1 and 2 Capacitor 1 Capacitive Oscillator Current 1 Capacitive Detection Sensitivity Capacitor 2 Capacitive Oscillator Current 2 Detection Frequency Lowpass Adjustable Gain 1 Adjustable Gain 2 Output Voltage Load Capacitor at PIN LPOUT 3dB Corner Frequency 1 3dB Corner Frequency 2 Temperature Coefficient VOUT (with input stages) Internal Resistors 1 and 2 Temperature Coefficient R01,02 Power Supply Rejection Ratio Namur Output Stage Threshold Voltage Output Resistance Temperature Coefficient ICC VSET ZOUT TKICC see Application Notes ZOUT = dVCC / dICC Tamb = -25 ... 85C, Namur: active 850 200 A1 A2 VLPOUT CLPOUT fC1 fC2 TKVOUT R01, R02 TKR01, R02 PSRR Tamb = -25 ... 85C VCC = 8V 18V; AGES = 1 R01 = 20k R02 = 20k VOUT = VLPOUT - VM, Tamb = -25 ... 85C 200 20 1.9 90 see Application Notes see Application Notes 1 1 1.1 CX1 IX1 CX CX2 IX2 fDET RCX1 = 400k CX = (CX2 - CX1 )/CX1 CX2 = CX1 (1 + CX ) RCX2 = 400k CL1 = CL2 =1nF, COSC = 20pF 10 4.75 5 10.5 4.75 5 5 COSC fOSC IOSC ROSC = 200k COSC = 2 CX1 20 1 9.5 10 VSTAB TKVSTAB VBG TKVBG VM TKVM Tamb = -25 ... 85C for internal usage only Tamb = -25 ... 85C for internal usage only Tamb = -25 ... 85C 1.9 1.23 4.27 4.5 100 1.30 100 2 100 Tamb Tst TJ -25 -55 Namur: not active, VSET = VM Namur: active, see Application Notes Conditions Min. 5 Typ. 8.2 0.9
CAN404
Max. 18 1.0 2.5
Unit V mA mA
85 125 150
C C C
4.73
V ppm/C
1.37
V ppm/C
2.15
V ppm/C
2200 150 10.8
pF kHz A
1000 5.38 100 2000 5.38 2
pF A % pF A kHz
10 10 3.3 50 8 8 V pF kHz kHz ppm/C k 10-3/C dB
VM
V k ppm/C
analog microelectronics
March 99 2/6
Converter IC for Capacitive Signals
BOUNDARY CONDITIONS
Parameter Current Sense Resistor Gain 1 Resistor Sum Gain 2 Resistor Sum VM Capacitor VSTAB Capacitor VBG Capacitor VCC Capacitor Namur Resistor Sum Set Resistor 1 (Capacitive Oscillator 1) Set Resistor 2 (Capacitive Oscillator 2) Set Resistor 3 (Reference Oscillator) Set Resistor 4 (Internal Power Supply) Set Resistor 5 (Reference Voltage 4.5V) Set Resistor 6 (Internal Stabilized Voltage) Symbol RM RL1+ RL2 RL3+ RL4 CVM CBG1 CBG2 CS RN1+ RN2 RCX1 RCX2 ROSC RSUP RBG1 RBG2 Min. 100 100 80 1.7 100 2.2 100 220 100 400 400 200 400 249 100 Typ.
CAN404
Max. 90 200 200 120 2.7
Unit k k nF F pF nF k k k
90 396 396 198 396 246 99
200
202 404 252 101
k k k k
For the performance of the entire system it is important that all Set Resistors have to have a small temperature coefficient. An offset compensation over temperature can only be achieved by choosing the resistors RCX1 and RCX2 with the same temperature coefficient and a very close placement of them in the entire circuit.
FUNCTIONAL DIAGRAM
COSC 16
Reference Oscillator fosc
VB+ 10
VS CS
COSC
CX1 18
VB-
CX1
CX2 20
Capacitive Oscillator 1 Capacitive Oscillator 2
V I
GND
9
IOUT RM RI Ground
8 Imax
CX2
VSTAB R01
Lowpass
R02
Internal Power Supply
VBG
19
RBG1
15
CBG2 CBG1
CL1 1
RL1 2
RL2 3
CL2 4
RL3 5
LPOUT 6
SET 7
VM 17
RCX1
RCX2 14
ROSC RSUP 13 12 11
RBG2
CL1 RL2
RL1
CL2 RL4
RCX1 RL3 RN2 RN1 CVM
RCX2
ROSC
RSUP
Figure 2
analog microelectronics
March 99 3/6
Converter IC for Capacitive Signals
FUNCTIONAL DESCRIPTION
CAN404
Basically the CAN404 is composed of two input stages, a signal processing unit and a voltage-tocurrent interface according to the Namur standard. A reference oscillator with a frequency, adjusted by the capacity COSC, drives two symmetrically built oscillators synchronously to its clock and its phase. The capacitors CX1 and CX2 determine the amplitude of the two driven oscillators. The difference of the oscillator amplitudes gives the relative change of the capacities CX1 and CX2 to each other with high common mode rejection and high resolution. This difference signal is rectified by a lowpass filter. The corner frequency and gain of it can be adjusted with a few external components. The output of the lowpass filter is connected to a voltage-to-current interface (Namur output). The maximum current of the output is adjustable externally. In Namur operation (Figure 2), the external reference point Ground is connected by the resistors RM and RI to the ground pin 10 of the IC (GND). The minimum supply voltage of the entire system VS depends on the minimum supply voltage VCC (5V) of the IC, the value of the input resistance RI of the power supply and the current sense resistor RM and has to fulfil the following relationship: VS VCC ,min + I OUT ,max (RI + RM ) The rated Namur operation is characterised by: VS,n = (8.2 0.1) V RI,n = (1000 10) Adjustment of CAN404: The zero adjustment of the differential output signal VOUT = VLPOUT - VM is made by the resistors RCX1 or RCX2 for the case that the two capacitors have nearly the same value CX2 CX1 (distance sensor without target). Therefore one of the resistors RCX1 or RCX2 is varied until the output voltage is zero: VOUT = 0 The greatest possible change of the capacitors CX2 = CX1 (1 + CX) (distance sensor with target) results in the maximum output signal that can be amplified by the lowpass. The maximum amplification is limited by the maximum allowed output voltage VLPOUT (see Electrical Specifications). In Namur operation, additional adjustments are required. The minimum output signal is VLPOUT,min = VM (for C X 1 = C X 2 and C X ,min = 0 ) (for C X 1 C X 2 and C X ,max = ( C X 2 - C X 1 ) / C X 1 )
The maximum output signal is amplified by the lowpass to a value of VLPOUT,max = 3.2V
The output current ICC consists of the supply current ICC,0 of the system and an additional component. The maximum output current at VLPOUT,max has to be adjusted to ICC,max = 2.5mA
analog microelectronics
March 99 4/6
Converter IC for Capacitive Signals
CAN404
For the minimum output current at VLPOUT,min, a typical value which is greater than the value of the supply current is chosen. That means ICC,min = 0.9mA The transfer function of the Namur output is adjusted by the resistor RM and the voltage VSET. The resistor RM is calculated by RM = VLPOUT ,max - VLPOUT ,min 10 I CC ,max - I CC ,min
(
)
The voltage VSET it is given by VSET = 1 V - 10 R M I CC ,min 11 LPOUT ,min RN 1 V M = -1 RN 2 VSET Sample calculations and typical values for the external components are listed in separate available Application Notes.
(
)
The voltage VSET has to be adjusted by the voltage divider RN1 and RN2:
analog microelectronics
March 99 5/6
Converter IC for Capacitive Signals
PINOUT
PIN
CL1 RL1 RL2 CL2 RL3 LPOUT SET GND VBVB+ 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 CX2 VSTAB CX1 VM COSC VBG RCX1 RCX2 ROSC RSUP
CAN404
NAME CL1 RL1 RL2 CL2 RL3 LPOUT SET GND VB- VB+ RSUP ROSC RCX2 RCX1 VBG COSC VM CX1 VSTAB CX2
BESCHREIBUNG Corner Frequency of Lowpass 1 Gain Adjustment Lowpass 1 Gain Adjustment Lowpass 1 Corner Frequency of Lowpass 2 Gain Adjustment Lowpass 2 Output Lowpass Voltage Setting of Namur Current Output IC Ground Power Supply (negative connection) Power Supply (positive connection) Current Definition of Internal Power Supply Current Definition of Reference Oscillator Current Adjustment of Capacitive Oscillator 2 Current Adjustment of Capacitive Oscillator 1 Internal Stabilised Voltage Capacitor of Reference Oscillator Reference Voltage 2V Oscillator Capacitor 1 Reference Voltage 4.5V Oscillator Capacitor 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Figure 3
DELIVERY
The CAN404 is available in version: * 20 pin DIL packages * SO20 (w) packages * Dice on 5" blue foil
The information provided herein is believed to be reliable; however, Analog Microelectronics assumes no responsibility for inaccuracies or omissions. Analog Microelectronics assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licences to any of the circuits described herein are implied or granted to any third party. Analog Microelectronics does not authorise or warrant any Analog Microelectronics product use in life support devices and/or systems.
analog microelectronics
March 99 6/6

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