LIA120
Optically Isolated
Linear Error Amplifier
INTEGRATED CIRCUITS DIVISION
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
Applications
• Power supply feedback
• Telecom central office supply
• Telecom bricks
• Modem transformer replacement
• Digital telephone isolation
Description
The LIA120 Optically Isolated Reference Amplifier
combines IXYS IC Division’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.
Block Diagram
By using the LIA120, system designers can save
precious board space and reduce component count.
Available in an 8-pin surface mount package.
NC
1
8 LED (Input)
K
2
7 COMP
A
3
6 FB
NC
4
5 GND
Approvals
• UL 1577 Recognized Component: File E76270
Ordering Information
DS-LIA120-R04
Part #
LIA120S
LIA120STR
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Description
8-Pin Surface Mount, Tubed (50/Tube)
8-Pin Surface Mount, Tape and Reel (1000/Reel)
1
INTEGRATED CIRCUITS DIVISION
LIA120
Absolute Maximum Ratings (@ 25ºC)
Parameter
Photodiode Cathode-Anode Voltage
Photodiode Anode-Cathode Voltage
Input Voltage
Input DC Current
Total Power Dissipation (note 1)
Operating Temperature
Symbol Ratings
VKAO
20
VAKO
0.5
VLED
9
20
ILED
PD
145
T
-40 to +85
Storage Temperature
1
T
Units
V
V
V
mA
mW
ºC
-40 to +125
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.
ºC
Derate linearly from 25°C at a rate of 2.42 mW/ °C.
Electrical Characteristics:
Parameter
Input Characteristics @ 25ºC
LED forward voltage
Reference voltage
Deviation of VREF over temperature - See Note 1
Transfer Characteristics @ 25ºC
Current Transfer Ratio in Feedback (IREF/ILED)
Current transfer ratio (IKA/ILED)
Current Transfer Ratio Matching (IKA/IREF)
Feedback input current
Deviation of IREF over temperature - See Note 1
Minimum drive current
Off-state error amplifier current
Error amplifier output impedance - See Note 2
Output Characteristics @ 25ºC
Cathode dark current
Cathode-Anode voltage breakdown
Isolation Characteristics @ 25ºC
Withstand insulation voltage
Resistance (input to output)
AC Characteristics @ 25ºC
Bandwidth (LED) - See Note 4
Common mode rejection ratio - See Note 5
Linearity
Conditions
Symbol
Min
Typ
Max
Units
ILED = 5 mA, VCOMP = VFB (Fig.1)
ILED = 10 mA, VCOMP = VFB (Fig.1)
TA = -40 to +85°C
TA = 25°C
TA = -40 to +85°C
VF
0.8
1.2
1.4
V
1.210
1.228
-
1.24
32
1.265
1.252
-
mV
2
2
100
226
110
0.001
0.21
3.0
3.0
115
0.1
-
%
%
%
µA
µA
mA
µA
VREF
VREF (DEV)
K1
K2
K3
V
ILED = 5mA, VREF = 0.5V (Fig.2)
ILED = 5 mA, VCOMP = VFB, VKA = 5 V (Fig. 4)
ILED = 5mA, VKA = 5.0V
ILED = 10 mA, R1 = 10 kΩ (Fig.2)
TA = -40 to +85°C
VCOMP = VFB (Fig.1)
VIN = 6 V, VFB = 0 (Fig.3)
ILED = 0.1 mA to 15 mA, VCOMP = VFB, f<1 kHz (Fig.1)
IREF (DEV)
ILED (MIN)
IOFF
IZOUTI
1.0
1.0
85
1
-
VIN = Open, VKA = 10V (Fig. 3)
IKA = 1µA
IKAO
BVKA
20
0.3
-
100
-
nA
V
RH ≤ 50%, TA = 25°C, t = 1 min (Note 3)
VI-O = 500 VDC (Note 3)
VISO
RI-O
3750
-
1012
-
Vrms
ILED = 1.0 mA, RL=100 kΩ, f=100 Hz (Fig. 5)
ILED = 5 mA, 100 mVPP
BW
CMRR
THD
-
100
70
70
-
kHz
dB
dB
IREF
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.
2
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R04
INTEGRATED CIRCUITS DIVISION
ILED
LIA120
ILED
8
VF
V
7
2
6
3
IREF
V
R1
VREF
2
6
3
5
FIG. 2. IREF TEST CIRCUIT
FIG. 1. VREF, VF, ILED (MIN) TEST CIRCUIT
ILED
8
7
2
6
3
8
IKA
IKAO
7
2
6
3
10V
VIN
V
7
VREF
5
IOFF
8
VKA
V
VCOMP
VREF
5
5
FIG. 3. IOFF, IKAO TEST CIRCUIT
FIG. 4. CTR TEST CIRCUIT
VCC = +5VDC
ILED
R1
100K
VOUT
8
2
7
3
6
5
_
VCM
+
10VPP
Fig. 5. CMRR Test Circuit
R04
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3
INTEGRATED CIRCUITS DIVISION
LIA120
PERFORMANCE DATA*
LED Current vs. Cathode Voltage
5
0
-5
-10
-0.5
0.0
0.5
1.0
1.5
VCOMP - Cathode Voltage (V)
I(OFF) - Off Current (nA)
200
150
100
2.0
1.0
-40
1.5
-20
0
20
40
60
80
0.5
-40
-20
0
20
40
60
80
IK - Cathode Current (PA)
VKA=10V
ILED=20mA
1000
30
20
10
0
800
600
ILED=10mA
400
ILED=5mA
200
ILED=1mA
0
-40
-20
0
20
40
60
80
-40
100
-20
0
20
40
60
80
100
1
2
3
4
5
6
VKA (V)
7
8
9
10
1.4
1.5
VKA=5V
3.0
2.5
2.0
1.5
TA=-5ºC
TA=25ºC
TA=55ºC
TA=85ºC
1.0
0.5
0
0
10
20
30
40
50
Voltage Gain vs. Frequency
40
30
20
10
40
RL=100:
20
0
0
0
1.3
60
Voltage Gain, A(Vo/Vin) dB
Frequency (kHz)
ILED=20mA
ILED=10mA
ILED=5mA
ILED=1mA
1.2
ILED - Forward Current (mA)
50
TA=25ºC
1.1
Current Transfer Ratio
vs LED Current
3.5
Bandwidth vs. Temperature for
High Frequency Applications
Cathode Current
vs. Photodiode Voltage
500
450
400
350
300
250
200
150
100
50
0
5
TA - Ambient Temperature (ºC)
TA - Ambient Temperature (ºC)
80
VF - Forward-Voltage (V)
VKA=5V
1200
40
60
10
0
1.0
100
Cathode Current
vs. Ambient Temperature
1400
40
85ºC
55ºC
25ºC
-5ºC
15
TA - Ambient Temperature (ºC)
50
20
20
1.0
100
0
LED Forward Current
vs. Forward Voltage
0
-40
-20
TA - Ambient Temperature (ºC)
1.5
Dark Current vs. Temperature
IKAO - Dark Current (nA)
0.5
VIN=10V
VFB=0
TA - Ambient Temperature (ºC)
IK - Cathode Current (PA)
1.18
0.0
(IKA / IF) - Current Transfer Ratio (%)
IREF - Reference Current (PA)
ILED=10mA
R1=10k:
250
-10
1.21
Off Current vs. Ambient Temperature
2.5
350
50
1.24
VCOMP - Cathode Voltage (V)
Reference Current vs.
Ambient Temperature
300
ILED = 10mA
1.37
ILED - Forward Current (mA)
-15
-1.0
1.30
150
TA=25ºC
120
VCOMP=VFB
90
60
30
0
-30
-60
-90
-120
-150
-0.5
-1.0
VREF - Reference Voltage (V)
TA=25ºC
VCOMP=VFB
ILED - Supply Current (PA)
ILED - Supply Current (mA)
15
10
Reference Voltage vs.
Ambient Temperature
LED Current vs. Cathode Voltage
0
10
20
30
40
50
60
Temperature (ºC)
70
80
90
10
100
Frequency (kHz)
1000
*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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R04
INTEGRATED CIRCUITS DIVISION
LIA120
PERFORMANCE DATA*
Noise Spectrum for 40dB Gain Setup
(220K/2.2K Gain)
Output Linearity
THD for 40dB Setup
Frequency (Hz)
-20
En (dBm/Hz)
Power (dB)
0
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
-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.
R04
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5
INTEGRATED CIRCUITS DIVISION
LIA120
VC
RL
8
100 Ω
+
2
VOUT
7
R1
CC
RC
+
3
6
VOUT
V in
R2
5
–
–
Fig. 6. Power Supply Feedback Application Circuit
8
VCC
2
100 Ω
V DD
R1
7
CC
3
VOUT
6
Ri
RC
RL
5
Vi
R2
Fig. 7. Non-inverting Linear Amplifier Circuit
6
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R04
INTEGRATED CIRCUITS DIVISION
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 device. 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 its 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.
ILED =
Vout,bias
RL K1
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:
R1 Vin
Vout R1
=
Vref RL
R2 Vref
R04
1
-1
K3
K3 is taken from the datasheet as 1 nominally. The AC
gain of the setup can be represented by:
AV VOUT /VIN
=
RL
R1
R2 R1
1
Gm CTRFB
1
Gm CTRForward
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
divider resistor’s impedance is becoming close to the
optical output impedance of the shunt regulator.
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:
Av, OPTICAL = Gm CTRFB R1 R2
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.
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7
INTEGRATED CIRCUITS DIVISION
LIA120
The bandwidth through the part will be:
BW Hz
=
Gm CTRFB R1 R2
1
*P5LED&C51 R2 +
P1
< BW Hz MAX
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.
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.
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R04
INTEGRATED CIRCUITS DIVISION
LIA120
Manufacturing Information
Moisture Sensitivity
All plastic encapsulated semiconductor packages are susceptible to moisture ingression. IXYS Integrated
Circuits Division classified all of its plastic encapsulated devices for moisture sensitivity according to
the latest version of the joint industry standard, IPC/JEDEC J-STD-020, in force at the time of product
evaluation. We test all of our products to the maximum conditions set forth in the standard, and guarantee proper
operation of our devices when handled according to the limitations and information in that standard as well as to any
limitations set forth in the information or standards referenced below.
Failure to adhere to the warnings or limitations as established by the listed specifications could result in reduced
product performance, reduction of operable life, and/or reduction of overall reliability.
This product carries a Moisture Sensitivity Level (MSL) rating as shown below, and should be handled according
to the requirements of the latest version of the joint industry standard IPC/JEDEC J-STD-033.
Device
Moisture Sensitivity Level (MSL) Rating
LIA120S
MSL 1
ESD Sensitivity
This product is ESD Sensitive, and should be handled according to the industry standard JESD-625.
Reflow Profile
This product has a maximum body temperature and time rating as shown below. All other guidelines of J-STD-020
must be observed.
Device
Maximum Temperature x Time
LIA120S
250ºC for 30 seconds
Board Wash
IXYS Integrated Circuits Division recommends the use of no-clean flux formulations. However, board washing to
remove flux residue is acceptable. Since IXYS Integrated Circuits Division employs the use of silicone coating as
an optical waveguide in many of its optically isolated products, the use of a short drying bake could be necessary
if a wash is used after solder reflow processes. Chlorine- or Fluorine-based solvents or fluxes should not be used.
Cleaning methods that employ ultrasonic energy should not be used.
R04
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9
INTEGRATED CIRCUITS DIVISION
LIA120
Mechanical Dimensions
LIA120S
9.652 ± 0.381
(0.380 ± 0.015)
2.540 ± 0.127
(0.100 ± 0.005)
0.635 ± 0.127
(0.025 ± 0.005)
3.302 ± 0.051
(0.130 ± 0.002)
9.525 ± 0.254
(0.375 ± 0.010)
6.350 ± 0.127
(0.250 ± 0.005)
Pin 1
0.457 ± 0.076
(0.018 ± 0.003)
PCB Land Pattern
2.54
(0.10)
8.90
(0.3503)
1.65
(0.0649)
7.620 ± 0.254
(0.300 ± 0.010)
0.254 ± 0.0127
(0.010 ± 0.0005)
0.65
(0.0255)
4.445 ± 0.127
(0.175 ± 0.005)
Dimensions
mm
(inches)
0.813 ± 0.102
(0.032 ± 0.004)
LIA120STR Tape & Reel
330.2 DIA.
(13.00 DIA.)
Top Cover
Tape Thickness
0.102 MAX.
(0.004 MAX.)
K0 =4.90
(0.193)
K1 =4.20
(0.165)
Embossed Carrier
Embossment
W=16.00
(0.63)
Bo=10.30
(0.406)
Ao=10.30
(0.406)
P=12.00
(0.472)
User Direction of Feed
Dimensions
mm
(inches)
NOTES:
1. Dimensions carry tolerances of EIA Standard 481-2
2. Tape complies with all “Notes” for constant dimensions listed on page 5 of EIA-481-2
For additional information please visit our website at: www.ixysic.com
IXYS Integrated Circuits Division 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 IXYS Integrated
Circuits Division’s Standard Terms and Conditions of Sale, IXYS Integrated Circuits Division 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 IXYS Integrated Circuits Division’s product may result in direct physical harm, injury, or death to a person or severe
property or environmental damage. IXYS Integrated Circuits Division reserves the right to discontinue or make changes to its products at any time without notice.
10
Specification: DS-LIA120-R04
©Copyright 2013, IXYS Integrated Circuits Division
All rights reserved. Printed in USA.
12/9/2013