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Optically Isolated Linear Error Amplifier
Features * Optocoupler, precision reference and error amplifier in single package * Low voltage operation 2.7V * 1.240V 2.5% reference * CTR Matching 15% * >70dB THD * 70dB CMRR * 3,750Vrms isolation * UL approval pending Description The LIA120 Optically Isolated Reference Amplifier combines Clare's linear optical coupler technology with an industry standard 431 type precision programmable shunt regulator to provide very linear high gain with excellent temperature stability for a total gain error of less than 2dB. By using optical feedback, the LIA120 essentially eliminates temperature and gain variations due to current transfer ratio (CTR) changes in optocouplers while increasing the bandwidth up to 10X and easing engineering design constraints. The LIA120 is very well suited for high gain feedback amplifiers that require excellent linearity and low temperature variation such as isolated power supply feedback stages, modem audio transformer replacement, isolated industrial control signals, and sensor feedback. By using the LIA120, system designers can save precious board space and reduce component count. Available in an 8 pin surface mount package. Ordering Information
Part # LIA120S LIA120STR
1 8 LED (Input)
LIA120
Applications * Power supply feedback * Telecom central office supply * Telecom bricks * Modem transformer replacement * Digital telephone isolation
Block Diagram
Description 8 Pin Surface Mount (50/Tube) Tape and Reel (1000/Reel)
NC
K
2
7 COMP
A
3
6 FB
NC
4
5 GND
DS-LIA120-R02.0
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1
LIA120
Absolute Maximum Ratings (@ 25 C)
Parameter Photodiode Cathode-Anode Voltage Photodiode Anode-Cathode Voltage Input Voltage Input DC Current Total Power Dissipation (note 1) Operating Temperature Storage Temperature
1
Symbol Ratings Units VKAO 20 V VAKO 0.5 V VLED 9 V ILED 20 mA PD 145 mW T -40 to +85 C T -40 to +125 C
Absolute Maximum Ratings are stress ratings. Stresses in excess of these ratings can cause permanent damage to the device. Functional operation of the device at conditions beyond those indicated in the operational sections of this data sheet is not implied.
Derate linearly from 25C at a rate of 2.42 mW/ C.
Electrical Characteristics:
Parameter Input Characteristics @ 25C LED forward voltage Reference voltage Conditions ILED = 5 mA, VCOMP = VFB (Fig.1) ILED = 10 mA, VCOMP = VFB (Fig.1) TA = -40 to +85C TA = 25C TA = -40 to +85C Symbol VF VREF Min 0.8 1.210 1.228 1.0 1.0 85 1 20 3750 Typ 1.2 1.24 32 2 2 100 226 110 0.001 0.21 0.3 1012 100 70 70 Max 1.4 1.265 1.252 3.0 3.0 115 0.1 100 Units V V mV % % % A A mA A Ohm nA V Vrms kHz dB dB
Deviation of VREF over temperature - See Note 1 VREF (DEV) Transfer Characteristics @ 25C Current Transfer Ratio in Feedback (IREF/ILED) ILED = 5mA, VREF = 0.5V (Fig.2) K1 K2 ILED = 5 mA, VCOMP = VFB, VKA = 5 V (Fig. 4) Current transfer ratio (IKA/ILED) Current Transfer Ratio Matching (IKA/IREF) ILED = 5mA, VKA = 5.0V K3 Feedback input current ILED = 10 mA, R1 = 10 k (Fig.2) IREF Deviation of IREF over temperature - See Note 1 TA = -40 to +85C IREF (DEV) Minimum drive current VCOMP = VFB (Fig.1) ILED (MIN) Off-state error amplifier current VIN = 6 V, VFB = 0 (Fig.3) IOFF Error amplifier output impedance - See Note 2 ILED = 0.1 mA to 15 mA, VCOMP = VFB, f<1 kHz (Fig.1) IZOUTI Output Characteristics @ 25C Cathode dark current VIN = Open, VKA = 10V (Fig. 3) IKAO IKA = 1A BVKA Cathode-Anode voltage breakdown Isolation Characteristics @ 25C Withstand insulation voltage RH 50%, TA = 25C, t = 1 min (Note 3) VISO Resistance (input to output) VI-O = 500 VDC (Note 3) RI-O AC Characteristics @ 25C Bandwidth (LED) - See Note 4 BW Common mode rejection ratio - See Note 5 ILED = 1.0 mA, RL = 100 k, f = 100 Hz (Fig. 5) CMRR Linearity ILED = 5 mA, 100 mVPP THD
1. The deviation parameters VREF(DEV) and IREF(DEV) are defined as the differences between the maximum and minimum values obtained over the rated temperature range. The average full-range temperature coefficient of the reference input voltage, VREF, is defined as: |VREF| (ppm/C) = {VREF (DEV)/VREF (TA 25C)} X 106 / TA T where TA is the rated operating free-air temperature range of the device. T 2. The dynamic impedance is defined as |ZOUT| = VCOMP/ILED, for the application circuit in Figure 6, |Zout| = K1R1 3. Device is considered as a two terminal device: Pins 1, 2, 3 and 4 are shorted together and Pins 5, 6, 7 and 8 are shorted together. 4. See compensation section for calculating bandwidth of LIA120. 5. Common mode transient immunity at output high is the maximum tolerable (positive) dVcm/dt on the leading edge of the common mode impulse signal, Vcm, to assure that the output will remain high. Common mode transient immunity at output low is the maximum tolerable (negative) dVcm/dt on the trailing edge of the common pulse signal,Vcm, to assure that the output will remain low.
2
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Rev. 2.0
LIA120
ILED VF
8
ILED IREF
8
7
2
7
2
V VREF
6
3
V R1
6
3
5
VREF
5
FIG. 1. VREF, VF, ILED (MIN) TEST CIRCUIT
FIG. 2. IREF TEST CIRCUIT
IOFF
8
ILED IKAO 10V
8
IKA
7 2
7
2
V
VIN
6
3
V
VCOMP VREF
6
3
VKA
5
5
FIG. 3. IOFF, IKAO TEST CIRCUIT
FIG. 4. CTR TEST CIRCUIT
VCC = +5VDC
ILED
8
R1 100K VOUT
2
7
3
6
5
_
VCM
+
10VPP
Fig. 5. CMRR Test Circuit
Rev. 2.0
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3
LIA120
PERFORMANCE DATA*
LIA120 Reference Voltage vs. Ambient Temperature
ILED = 10mA
15 ILED - Supply Current (mA) 10 5 0 -5 -10
LIA120 LED Current vs. Cathode Voltage
ILED - Supply Current (A)
-15 -1.0
-0.5
0.0
0.5
1.0
1.5
150 120 90 60 30 0 -30 -60 -90 -120 -150 -1.0
LIA120 LED Current vs. Cathode Voltage
1.30 VREF - Reference Voltage (V) -0.5 0.0 0.5 1.0 1.5 1.37 1.24 1.21 1.18
-40
-20
0
20
40
60
80
VCOMP - Cathode Voltage (V)
VCOMP - Cathode Voltage (V)
55C
25C
IREF - Reference Current (A)
I(OFF) - Off Current (nA)
300 250 200 150 100 50
2.0 1.5 1.0 0.5 0
ILED - Forward Current (mA)
350
LIA120 Reference Current vs. Ambient Temperature
ILED = 10mA R1 = 10 k
2.5
LIA120 Off Current vs. Ambient Temperature
VIN = 10V VFB = 0
20 15 10 5
LIA120 LED Forward Current vs. Forward Voltage
85C -5C
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
0 1.0
1.1
1.2
1.3
1.4
1.5
VF - Forward-Voltage (V)
50 IKAO - Dark Current (nA) 40 30 20 10 0 -10
(IKA/IF) - Current Transfer Ratio (%)
LIA120 Dark Current vs. Temperature
VKA = 10V IK - Cathode Current (A)
1400 1200 1000 800 600 400 200 0
LIA120 Cathode Current vs. Ambient Temperature
VKA = 5V ILED = 20mA
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
LIA120 Current Transfer Ratio vs LED Current
VKA = 5V
ILED = 10mA ILED = 5mA ILED = 1mA -40 -20 0 20 40 60 80 100
-40
-20
0
20
40
60
80
100
0
10
20
30
40
50
ILED - Forward Current (mA)
500 450 400 350 300 250 200 150 100 50 0
LIA120 Cathode Current vs. Photodiode Voltage
50 ILED = 20mA Frequency (kHz) 40 30 20 10 0
LIA120 Bandwidth vs. Temperature for High Frequency Applications
Voltage Gain, A(Vo/Vin) dB
60
LIA120 Voltage Gain vs. Frequency
IK - Cathode Current (A)
40
ILED = 10mA ILED = 5mA ILED = 1mA 0 1 2 3 4 5 6 7 8 9 10
20
0
10
20
30
40
50
60
70
80
90
0
10
100 Frenquency kHz
1000
VKA (V)
*The Performance data shown in the graphs above is typical of device performance. For guaranteed parameters not indicated in the written specifications, please contact our application department.
4
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Rev. 2.0
LIA120
PERFORMANCE DATA*
LIA120 Output Linearity THD for 40dB Setup
0.00E+00 -1.00E+01 -2.00E+01 -3.00E+01 -4.00E+01 -5.00E+01 -6.00E+01 -7.00E+01 -8.00E+01 -9.00E+01 -1.00E+02 1.0E+ 2.0E+ 3.0E+ 4.0E+ 5.0E+ 6.0E+ 7.0E+ 8.0E+ 9.0E+ 03 03 03 03 03 03 03 03 03 Frequency (Hz)
LIA120 Noise Spectrum for 40dB Gain Setup (220K/2.2K Gain)
0 -20 E n ( dB m / H z ) -40 -60 -80 -100 -120 -140 1.000E+02 1.000E+03 1.000E+04 1.000E+05 Frequency (Hz) Input Spectrum at FB Output Spectrum
*The Performance data shown in the graphs above is typical of device performance. For guaranteed parameters not indicated in the written specifications, please contact our application department.
Rev. 2.0
Power (dB)
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5
LIA120
VC
RL
8
100
+
VOUT
+
2
7
3
6
CC RC
R1
V in
VOUT
5
-
R2
-
Fig. 6. Power Supply Feedback Application Circuit
VCC
2
8
100 R1 CC RC R2 Ri
V DD
7
VOUT RL
3
6
Vi
5
Fig. 7. Non-inverting Linear Amplifier Circuit
6
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Rev. 2.0
LIA120
The LIA120 The LIA120 is an optically-coupled isolated linear error amplifier. It integrates three of the most fundamental elements necessary to make an isolated power supply: a reference voltage, an error amplifier, and an isolated coupling devices. It is functionally equivalent to a 431 type shunt regulator plus a linear optical amplifier. Powering the Isolated Input The isolated input of the LIA120 is powered through the LED pin (pin 8) via the part to it's isolated ground at pin 5. The typical operating current of the device is determined by the output voltage and current requirements as well as the CTR of the linear optocoupler. For Figure 7, the LED current requirement is set by the following equation. Vout, bias ILED RL * K1 The output voltage R typically constrained by the user to is R1 1 1 satisfy the design requirements of the application circuit. R2 K3 Design considerations must also take into account that RL affects the total gain and that CTR gains vary with process. Nominally the K3 current should be around LED R1 1-2mA but can be as high as 10-15mA if the user requires. LED current is limited by the resistor in series with mpin 8, VOUT VIN * the LED pin, to the supply and is typically 10-100 ohms for operating currents of 1-2mA. The minimum operating m voltage of 2.74V for the LIA120 from pin 8 to pin 5 is based on the sum of the voltage drop of the R CTRFB R1 LED and 2 the operational voltage headroom of the 431. Minimum R1 R2 operating voltage for the application circuit is therefore the sum of the LIA120 minimum operating voltage plus RLED C R the voltage drop of the current limiting resistor cFor1 aR2 P 1 design with 1mA of LED current and a current limiting resistor of 100 ohms, the minimum operating voltage is calculated to be 2.74 + (0.001)(100) = 2.84V. Feedback Setting the gain for the LIA120 is accomplished simply Vout, bias ILED by setting two resistors. The application circuit in Vout, bias IRL * K resistor LED Figure 6 shows a 1R * K divider feeding the FB pin, so L the operating conditions1 for the gain are governed by: R1 R1 1 R1 R 1 R2 K31 R2 K3 K3 is taken from the datasheet as 1 nominally. The ac K3 R1 K3 gain of the setup canRbe represented by:
1
Where: * Gm = 1/ZOUT which is ~ 3 Siemens * CTRFB is approximately CTRForward = 0.02 nominally CTRFB = K1, CTRFORWARD = K2, CTRFORWARD/CTRFB = K3 This calculation provides a more accurate gain calculation but is only necessary when the voltage Vout, bias ILED divider resistor's impedance is becoming close to the RL * K1 optical output impedance of the shunt regulator.
R1 R1 1 Compensation R2 K3 The LIA120 is relatively easy to compensate but two factors must be considered when analyzing the circuit. K3 The frequency response of the LIA120 can be as high R1 as 40kHz, but must be limited because of the closed loop optical feedback to the input signal. In the localized optical feedback there are two poles to consider, the 431 m dominant pole VOUT the linear * and VIN optical coupler pole. The open loop gain of the optical loop (for the application diagram) is: m Vout, bias CTRFB R1 R2
ILED R1 R2 RL K1 The open *loop gain is affected by the selection of R1 and R2 and without any compensation the circuit may RLED Cc R1 R2 R1 R1 P1 oscillate. The addition of 1 compensation network (Cc a R2 Rc) control the maximum bandwidth so that open K3 and loop gain is rolling off long before the optical pole causes the circuit to oscillate. The optical pole is at ~180kHz so K3 R1 the bandwidth is typically limited to less than 40kHz.
While there is flexibility in the part to change the compensation technique, the upper limit on frequency m VOUT VIN * response is generally desired to be such that the circuit will not oscillate for a large selection of R1 and R2. m Therefore the compensation capacitor should not be less than 100pF which gives adequate bandwidth for most CTRFB R1 R2 designs. The bandwidth through the part will be:
R1 R2 RLED Cc R1 R2 P1
Where: P1 max is 1kHz (6.28krad/s) due to the internal compensation of the 431. CTR is the current transfer ratio of the feedback optocoupler (0.001-0.003). RLED is the combined impedance of the limiting resistor and the LED resistance (25 ohms) and Gm is the transconductance of the 431 (3 Siemens). However, since some of these elements vary over operating conditions and temperature, the bandwidth should be practically limited to less than 40kHz to avoid oscillations, which is the value computed by 100pF.
VOUT VIN * VOUT VIN
m
*
m m
m
Rev. 2.0
CTRFB R1 R2 CTRFB R1 R2 R1 R2
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RR
7
LIA120
Photodiode The output of the LIA120 is a photodiode capable or withstanding high voltages. For the most accurate results, attempt to bias the voltage across the cathode anode the same as VREF. The load resistors can be placed in series with the cathode or anode for desired output polarity. Manufaturing Information Soldering Recommended soldering processes are limited to 245C component body temperature for 10 seconds. Washing Clare does not recommend ultrasonic cleaning or the use of chlorinated solvents.
8
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Rev. 2.0
MECHANICAL DIMENSIONS
8 Pin Surface Mount ("S" Suffix) PC Board Pattern (Top View)
Tape and Reel Packaging for 8 Pin Surface Mount Package
330.2 DIA. (13.00) Top Cover Tape Thickness 0.102 MAX. (0.004)
W = 16.30 max (0.642 max) BO = 10.30 (0.406) Top Cover Tape
Embossed Carrier
Embossment
K1 = 4.20 (0.165) K0 = 4.90 (0.193)
P = 12.00 (0.472) User Direction of Feed
AO = 10.30 (0.406)
NOTE: Tape dimensions not shown, comply with JEDEC Standard EIA-481-2
Dimensions: mm (inches) For additional information please visit our website at: www.clare.com
Clare, Inc. makes no representations or warranties with respect to the accuracy or completeness of the contents of this publication and reserves the right to make changes to specifications and product descriptions at any time without notice. Neither circuit patent licenses nor indemnity are expressed or implied. Except as set forth in Clare's Standard Terms and Conditions of Sale, Clare, Inc. assumes no liability whatsoever, and disclaims any express or implied warranty, relating to its products including, but not limited to, the implied warranty of merchantability, fitness for a particular purpose, or infringement of any intellectual property right. The products described in this document are not designed, intended, authorized or warranted for use as components in systems intended for surgical implant into the body, or in other applications intended to support or sustain life, or where malfunction of Clare's product may result in direct physical harm, injury, or death to a person or severe property or environmental damage. Clare, Inc. reserves the right to discontinue or make changes to its products at any time without notice.
Specification: DS-LIA120-R02.0 (c)Copyright 2005, Clare, Inc. All rights reserved. Printed in USA. 2/17/05

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