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DS-LIA120-R02.0 1
LIA120
Optically Isolated Linear Error Amplifier
Part # Description
LIA120S 8 Pin Surface Mount (50/Tube)
LIA120STR Tape and Reel (1000/Reel)
Applications
Features Description
Ordering Information
Block Diagram
• Power supply feedback
• Telecom central office supply
• Telecom bricks
• Modern transformer replacement
• Digital telephone isolation
• 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
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.
1
2
3
4 5
6
7
8LED (Input)
FB
COMP
GND
NC
K
A
NC
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2
LIA120
Rev. 2.0
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.
Parameter Conditions Symbol Min Typ Max Units
Input Characteristics @ 25°C
LED forward voltage ILED = 5 mA, VCOMP = VFB (Fig.1) VF0.8 1.2 1.4 V
Reference voltage ILED = 10 mA, VCOMP = VFB (Fig.1)
TA = -40 to +85°C VREF
1.210 - 1.265 V
TA = 25°C 1.228 1.24 1.252
Deviation of VREF over temperature - See Note 1 TA = -40 to +85°C VREF (DEV) - 32 - mV
Transfer Characteristics @ 25°C
Current Transfer Ratio in Feedback (IREF/ILED) ILED = 5mA, VREF = 0.5V (Fig.2) K11.0 2 3.0 %
Current transfer ratio (IKA/ILED) ILED = 5 mA, VCOMP = VFB, VKA = 5 V (Fig. 4) K21.0 2 3.0 %
Current Transfer Ratio Matching (IKA/IREF) ILED = 5mA, VKA = 5.0V K385 100 115 %
Feedback input current ILED = 10 mA, R1 = 10 kΩ (Fig.2) IREF - 226 - µA
Deviation of IREF over temperature - See Note 1 TA = -40 to +85°C IREF (DEV) - 110 - µA
Minimum drive current VCOMP = VFB (Fig.1) ILED (MIN) 1 - - mA
Off-state error amplifier current VIN = 6 V, VFB = 0 (Fig.3) IOFF - 0.001 0.1 µA
Error amplifier output impedance - See Note 2 ILED = 0.1 mA to 15 mA, VCOMP = VFB, f<1 kHz (Fig.1) IZOUTI - 0.21 - Ohm
Output Characteristics @ 25°C
Cathode dark current VIN = Open, VKA = 10V (Fig. 3) IKAO - 0.3 100 nA
Cathode-Anode voltage breakdown IKA = 1µA BVKA 20 - - V
Isolation Characteristics @ 25°C
Withstand insulation voltage RH ≤ 50%, TA = 25°C, t = 1 min (Note 3) VISO 3750 - - Vrms
Resistance (input to output) VI-O = 500 VDC (Note 3) RI-O - 1012 -Ω
AC Characteristics @ 25°C
Bandwidth (LED) - See Note 4 BW- 100 - kHz
Common mode rejection ratio - See Note 5 ILED = 1.0 mA, RL = 100 kΩ, f = 100 Hz (Fig. 5) CMRR - 70 - dB
Linearity ILED = 5 mA, 100 mVPP THD - 70 - dB
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 25°C)} X 106 / ∆TA
where ∆TA is the rated operating free-air temperature range of the device.
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.
Electrical Characteristics:
Parameter Symbol Ratings Units
Photodiode Cathode-Anode Voltage VKAO 20 V
Photodiode Anode-Cathode Voltage VAKO 0.5 V
Input Voltage VLED 9 V
Input DC Current ILED 20 mA
Total Power Dissipation (note 1) PD145 mW
Operating Temperature T -40 to +85 °C
Storage Temperature T -40 to +125 °C
Absolute Maximum Ratings (@ 25˚ C)
1 Derate linearly from 25°C at a rate of 2.42 mW/ °C.
˜
LIA120
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Rev. 2.0
R1
FIG. 1. VREF, VF, ILED (MIN) TEST CIRCUIT FIG. 2. IREF TEST CIRCUIT
FIG. 4. CTR TEST CIRCUIT
FIG. 3. IOFF, IKAO TEST CIRCUIT
VCC = +5VDC
VOUT
VCM
10VPP
R1
100K
+
_
Fig. 5. CMRR Test Circuit
ILED
VF
2
3
5
6
7
8
V
VREF
ILED
2
3
5
6
7
8
V
VREF
ILED
IREF
VREF
VKA
VIN
2
3
5
6
7
8
V
10V
IOFF
IKAO
2
3
5
6
7
8
VCOMP
2
3
5
6
7
8
V
ILED
IKA
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4
LIA120
Rev. 2.0
PERFORMANCE DATA*
*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.
LIA120
LED Current vs. Cathode Voltage
VCOMP - Cathode Voltage (V)
ILED - Supply Current (mA)
-1.0
15
10
5
0
-5
-10
-15
-0.5 0.0 0.5 1.0 1.5
LIA120
LED Current vs. Cathode Voltage
VCOMP - Cathode Voltage (V)
ILED - Supply Current (µA)
-1.0
150
120
90
60
30
0
-30
-60
-90
-120
-150
-0.5 0.0 0.5 1.0 1.5
LIA120
Reference Voltage vs.
Ambient Temperature
VREF - Reference Voltage (V)
-40
1.30
1.37
1.24
1.21
1.18
-20 0 20 40 60 80
ILED = 10mA
LIA120
Reference Current vs.
Ambient Temperature
IREF - Reference Current (µA)
-40
350
300
250
200
150
100
50
-20 0 20 40 60 80 100
ILED = 10mA
R1 = 10 kΩ
LIA120
Off Current vs. Ambient Temperature
I(OFF) - Off Current (nA)
-40
2.5
2.0
1.5
1.0
0.5
0
-20 0 20 40 60 80 100
VIN = 10V
VFB = 0
LIA120
LED Forward Current vs. Forward Voltage
ILED - Forward Current (mA)
VF - Forward-Voltage (V)
20
15
10
5
0
1.0 1.1 1.2 1.3 1.4 1.5
85ºC
55ºC
25ºC
-5ºC
LIA120
Dark Current vs. Temperature
IKAO - Dark Current (nA)
VKA = 10V
-40
50
40
30
20
10
0
-10
-20 0 20 40 60 80 100
LIA120
Cathode Current vs. Ambient Temperature
IK - Cathode Current (µA)
VKA = 5V
ILED = 20mA
ILED = 10mA
ILED = 5mA
ILED = 1mA
-40
1400
1200
1000
800
600
400
200
0
-20 0 20 40 60 80 100
LIA120
Cathode Current vs. Photodiode Voltage
IK - Cathode Current (µA)
VKA (V)
0
500
450
400
350
300
250
200
150
100
50
0
12345678910
ILED = 20mA
ILED = 10mA
ILED = 5mA
ILED = 1mA
LIA120
Bandwidth vs. Temperature for
High Frequency Applications
Frequency (kHz)
0
50
40
30
20
10
0
10 20 30 40 50 60 70 80 90
LIA120
Voltage Gain vs. Frequency
Voltage Gain, A(Vo/Vin) dB
Frenquency kHz
10
60
40
20
0
100 1000
LIA120
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Rev. 2.0
PERFORMANCE DATA*
*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.
LIA120
Output Linearity
THD for 40dB Setup
-1.00E+02
-9.00E+01
-8.00E+01
-7.00E+01
-6.00E+01
-5.00E+01
-4.00E+01
-3.00E+01
-2.00E+01
-1.00E+01
0.00E+00
1.0E+
03
2.0E+
03
3.0E+
03
4.0E+
03
5.0E+
03
6.0E+
03
7.0E+
03
8.0E+
03
9.0E+
03
Frequency (Hz)
)
B
d
(
rewoP
LIA120
Noise Spectrum for 40dB Gain Setup
(220K/2.2K Gain)
-140
-120
-100
-80
-60
-40
-20
0
1.000E+02 1.000E+03 1.000E+04 1.000E+05
Frequency (Hz)
)zH/m
B
d
(
nE
Input Spectrum at FB
Output Spectrum
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6
LIA120
Rev. 2.0
VC
VCC
Vin
100Ω
VOUT
+
VOUT
VOUT
RL
R1
RC
CC
R2
Fig. 6. Power Supply Feedback Application Circuit
Fig. 7. Non-inverting Linear Amplifier Circuit
Vi
VDD
Ri
R2
R1
RC
CC
RL
+
–
–
100 Ω
2
3
5
6
7
8
2
3
5
6
7
8
LIA120
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Rev. 2.0
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.
The output voltage is typically constrained by the user to
satisfy the design requirements of the application circuit.
Design considerations must also take into account that
RL affects the total gain and that CTR gains vary with
process. Nominally the LED current should be around
1-2mA but can be as high as 10-15mA if the user
requires.
LED current is limited by the resistor in series with pin 8,
the LED pin, to the supply and is typically 10-100 ohms
for operating currents of 1-2mA. The minimum operating
voltage of 2.74V for the LIA120 from pin 8 to pin 5 is
based on the sum of the voltage drop of the LED and
the operational voltage headroom of the 431. Minimum
operating voltage for the application circuit is therefore
the sum of the LIA120 minimum operating voltage plus
the voltage drop of the current limiting resistor For a
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
by setting two resistors. The application circuit in
Figure 6 shows a resistor divider feeding the FB pin, so
the operating conditions for the gain are governed by:
K3 is taken from the datasheet as 1 nominally. The ac
gain of the setup can be represented by:
Compensation
The LIA120 is relatively easy to compensate but two
factors must be considered when analyzing the circuit.
The frequency response of the LIA120 can be as high
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
dominant pole and the linear optical coupler pole. The
open loop gain of the optical loop (for the application
diagram) is:
The open loop gain is affected by the selection of R1
and R2 and without any compensation the circuit may
oscillate. The addition of a compensation network (Cc
and Rc) control the maximum bandwidth so that open
loop gain is rolling off long before the optical pole causes
the circuit to oscillate. The optical pole is at ~180kHz so
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
response is generally desired to be such that the circuit
will not oscillate for a large selection of R1 and R2.
Therefore the compensation capacitor should not be less
than 100pF which gives adequate bandwidth for most
designs. The bandwidth through the part will be:
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.
This calculation provides a more accurate gain
calculation but is only necessary when the voltage
divider resistor’s impedance is becoming close to the
optical output impedance of the shunt regulator.
m
m
RL • K1
•
R11
R1
VOUT VIN
R1R2
CTRFB
RLED Cc
R1R2
P1
R1R2
R1
K3
K3
R2
Vout, bias
ILED
m
m
RL • K1
•
R11
R1
VOUT VIN
R1R2
CTRFB
RLED Cc
R1R2
P1
R1R2
R1
K3
K3
R2
Vout, bias
ILED
m
m
RL • K1
•
R11
R1
VOUT VIN
R1R2
CTRFB
RLED Cc
R1R2
P1
R1R2
R1
K3
K3
R2
Vout, bias
ILED
m
m
RL • K1
•
R11
R1
VOUT VIN
R1R2
CTRFB
RLED Cc
R1R2
P1
R1R2
R1
K3
K3
R2
Vout, bias
ILED
m
m
RL • K1
•
R11
R1
VOUT VIN
R1R2
CTRFB
RLED Cc
R1R2
P1
R1R2
R1
K3
K3
R2
Vout, bias
ILED
Where:
• Gm = 1/ZOUT which is ~ 3 Siemens
• CTRFB is approximately CTRForward = 0.02 nominally
CTRFB = K1, CTRFORWARD = K2, CTRFORWARD/CTRFB = K3
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8
LIA120
Rev. 2.0
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
245ºC component body temperature for 10 seconds.
Washing
Clare does not recommend ultrasonic cleaning or the
use of chlorinated solvents.
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
©Copyright 2005, Clare, Inc.
All rights reserved. Printed in USA.
2/17/05
For additional information please visit our website at: www.clare.com
MECHANICAL DIMENSIONS
PC Board Pattern
(Top View)
Dimensions:
mm
(inches)
Tape and Reel Packaging for 8 Pin Surface Mount Package
K0 = 4.90
(0.193)
K1 = 4.20
(0.165)
Top Cover
Tape
P = 12.00
(0.472)
User Direction of Feed
NOTE: Tape dimensions not shown, comply with JEDEC Standard EIA-481-2
Embossment
Embossed Carrier
Top Cover
Tape Thickness
0.102 MAX.
(0.004)
330.2 DIA.
(13.00)
AO = 10.30
(0.406)
BO = 10.30
(0.406)
W = 16.30 max
(0.642 max)
8 Pin Surface Mount (“S” Suffix)