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DS-LIA120-R01.0 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
uses Clare’s linear optical coupler technology and
the IX431 precision programmable shunt regulator
to provide very linear high gain signals with excellent
temperature stability for a total gain error of less
than 2dB. By using a linear optocoupler, the LIA120
essentially eliminates temperature and gain variations
due to current transfer ratio (CTR) changes in the
optocouplers, increases the bandwidth up to 10X, and
eases engineering design constraints.
The LIA120 is very well suited for high gain
feedback amplifiers that require excellent linearity
and low temperature variation, like 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. 1.0
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 VCOMP = VFB, ILED = 10 mA (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 (IKA/ILED) ILED = 5 mA, VCOMP = VFB, VKA = 5 V (Fig. 4) K11.0 2 3.0 %
Current Transfer Ratio in Feedback (IREF/ILED) ILED = 5mA, VREF = 0.5V (Fig.2) 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) I (OFF) - 0.001 0.1 µA
Error amplifier output impedance - See Note 2 VCOMP = VFB, ILED = 0.1 mA to 15 mA, f<1 kHz 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 ID = 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 fig. 9, |Zout| = K2R1
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
Storage Temperature T -40 to +125 °C
Operating Temperature T -40 to +85 °C
Input Voltage VLED 9 V
Input DC Current ILED 20 mA
Photodiode Cathode-Anode Voltage VKAO 20 V
Photodiode Anode-Cathode Voltage VAKO 0.5 V
Total Power Dissipation (note 1) PD145 mW
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. 1.0
ILED
VIN
VCOMP
IKAO
ID
VKA
VREF
VF
VREF
8 2
3
V
V
10V
7
6
5
ILED
IOFF
IREF
8
7
2
3
2
3
V
V
6
5
8
7
6
5
8
7
2
3
6
5
R1
FIG. 1. V
REF
, V
F,
I
LED
(min) TEST CIRCUIT FIG. 2. I
REF
TEST CIRCUIT
FIG. 4. CTR TEST CIRCUIT
FIG. 3. I
OFF KAO
I TEST CIRCUIT
3
2
1
4
8
7
6
5
VCC = +5V DC
VOUT
VCM
10VP-P
R1
100K
+
_
Fig. 5 CMRR Test Circuit
VREF
ILED
ILED
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4
LIA120
Rev. 1.0
3
2
1
4
8
7
6
5
3
4
2
1
6
5
7
8
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
RB2
RB1
RC
CC
RL
+
–
–
100Ω
LIA120
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Rev. 1.0
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
Current Transfer Ratio vs LED Current
(IKA/IF) - Current Transfer Ratio (%)
ILED - Forward Current (mA)
VKA = 5V
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
10 20 30 40 50
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
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6
LIA120
Rev. 1.0
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
LIA120
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Rev. 1.0
The LIA120
The LIA120 is an optically isolated error amplifier. It
incorporates three of the most common elements
necessary to make an isolated power supply: a
reference voltage, and error amplifier, and a linear
optocoupler. It is functionally equivalent to the IX431
shunt regulator plus a linear optocoupler.
Powering the isolated input
The isolated input of the LIA120 is powered through
the LED pin (pin 8) through the part to it’s isolated
ground. The typical operating current in the device
is dictated by the output voltage and output current
requirements, and the CTR of the linear optocoupler.
The output voltage is typically constrained by the
user, RL also affects the total gain, and CTR varies
with process, but the nominal LED current should be
around 1-2mA, and can be as high as 10mA-15mA if
the user requires.
The LED current is limited by a resistor in series with
the LED pin to the supply and is typically 10-100
ohms for operating currents of 1-2mA. The current
limiting resistor, in conjunction with the LED voltage,
and voltage headroom of the IX431 sets the minimum
operating voltage of the isolated input to 2.74V plus
the drop of the limiting resistor.
Feedback
Setting the gain for the LIA120 is accomplished simply
by setting two resistors. The application circuit 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:
Where:
• Gm = 1/ZKA which is ~ 3 Siemens
• CTRFB is approximately CTRForward = 0.02 nominally
CTRFB/CTRForward = K3
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 signals.
In the localized optical feedback there are two poles
to consider, the IX431 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 limited to typically
<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 IX431
CTR is the current transfer ratio of the feedback
optocoupler (0.025 – 0.005)
RLED is the combined impedance of the limiting
resistor and the LED resistance (25 Ohms)
Gm is transconductance of the IX431 (3 Siemens)
However, since some of these elements vary over
operating conditions and temperature, the bandwidth
should be practically limited to <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
m
m
m
m
m
m
m
m
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8
LIA120
Rev. 1.0
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-R01.0
©Copyright 2004, Clare, Inc.
All rights reserved. Printed in USA.
11/15/04
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)