LIA120
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.
Applications
• Power supply feedback
• Telecom central office supply
• Telecom bricks
• Modem transformer replacement
• Digital telephone isolation
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
Block Diagram
DS-LIA120-R02.0
Part #
LIA120S
LIA120STR
NC
1
8 LED (Input)
K
2
7 COMP
A
3
6 FB
NC
4
5 GND
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Description
8 Pin Surface Mount (50/Tube)
Tape and Reel (1000/Reel)
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 25°C at a rate of 2.42 mW/ °C.
Electrical Characteristics:
Parameter
Input Characteristics @ 25°C
LED forward voltage
Reference voltage
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
1.0
1.0
85
1
-
2
2
100
226
110
0.001
0.21
3.0
3.0
115
0.1
-
%
%
%
µA
µA
mA
µA
Ohm
20
0.3
-
100
-
nA
V
3750
-
1012
-
Vrms
Ω
-
100
70
70
-
kHz
dB
dB
VREF
Deviation of VREF over temperature - See Note 1
VREF (DEV)
Transfer Characteristics @ 25°C
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 kΩ (Fig.2)
IREF
Deviation of IREF over temperature - See Note 1
TA = -40 to +85°C
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 @ 25°C
Cathode dark current
VIN = Open, VKA = 10V (Fig. 3)
IKAO
IKA = 1µA
BVKA
Cathode-Anode voltage breakdown
Isolation Characteristics @ 25°C
Withstand insulation voltage
RH ≤ 50%, TA = 25°C, t = 1 min (Note 3)
VISO
Resistance (input to output)
VI-O = 500 VDC (Note 3)
RI-O
AC Characteristics @ 25°C
Bandwidth (LED) - See Note 4
BW
Common mode rejection ratio - See Note 5
ILED = 1.0 mA, RL = 100 kΩ, f = 100 Hz (Fig. 5)
CMRR
Linearity
ILED = 5 mA, 100 mVPP
THD
V
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 / ∆TTA
where ∆TTA 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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Rev. 2.0
LIA120
ILED
ILED
8
VF
V
VREF
7
2
6
3
IREF
V
R1
V
VIN
7
2
6
3
VREF
5
5
FIG. 2. IREF TEST CIRCUIT
FIG. 1. VREF, VF, ILED (MIN) TEST CIRCUIT
IOFF
8
ILED
8
7
2
6
3
8
IKA
IKAO
7
2
6
3
10V
V
VCOMP
VREF
5
FIG. 3. IOFF, IKAO TEST CIRCUIT
VKA
5
FIG. 4. CTR TEST CIRCUIT
VCC = +5VDC
ILED
R1
100K
VOUT
8
2
7
3
6
5
_
VCM
+
10VPP
Fig. 5. CMRR Test Circuit
Rev. 2.0
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3
LIA120
PERFORMANCE DATA*
LIA120
LED Current vs. Cathode Voltage
10
5
0
-5
-10
0.5
1.0
1.5
-0.5
I(OFF) - Off Current (nA)
IREF - Reference Current (µA)
2.5
ILED = 10mA
R1 = 10 kΩ
300
250
200
150
100
50
-20
0
20
40
60
1.0
1.5
1.21
1.18
-40
-20
0
20
40
60
80
80
LIA120
LED Forward Current vs. Forward Voltage
LIA120
Off Current vs. Ambient Temperature
20
VIN = 10V
VFB = 0
2.0
1.5
1.0
0.5
0
-40
0.5
1.24
VCOMP - Cathode Voltage (V)
LIA120
Reference Current vs.
Ambient Temperature
350
0.0
1.37
100
-40
-20
0
20
40
60
80
100
85ºC
25ºC
0.0
VCOMP - Cathode Voltage (V)
ILED = 10mA
55ºC
-0.5
1.30
ILED - Forward Current (mA)
-15
-1.0
150
120
90
60
30
0
-30
-60
-90
-120
-150
-1.0
VREF - Reference Voltage (V)
ILED - Supply Current (µA)
ILED - Supply Current (mA)
15
LIA120
Reference Voltage vs.
Ambient Temperature
LIA120
LED Current vs. Cathode Voltage
-5ºC
15
10
5
0
1.0
1.1
1.2
1.3
1.4
1.5
LIA120
Dark Current vs. Temperature
LIA120
Cathode Current vs. Ambient Temperature
1400
VKA = 10V
IK - Cathode Current (µA)
IKAO - Dark Current (nA)
50
ILED = 20mA
1000
30
20
10
0
-10
VKA = 5V
1200
40
-40
-20
0
20
40
60
80
800
600
ILED = 5mA
200
0
100
ILED = 10mA
400
ILED = 1mA
-40
-20
0
20
40
60
80
100
(IKA/IF) - Current Transfer Ratio (%)
VF - Forward-Voltage (V)
3.5
3.0
LIA120
Current Transfer Ratio vs LED Current
VKA = 5V
2.5
2.0
1.5
1.0
0.5
0
0
10
20
30
40
50
ILED - Forward Current (mA)
LIA120
Bandwidth vs. Temperature for
High Frequency Applications
ILED = 20mA
ILED = 10mA
ILED = 5mA
40
30
20
10
ILED = 1mA
0
1
2
3
4
5
6
7
8
9
10
0
0
10
20
30
40
50
60
VKA (V)
70
80
LIA120
Voltage Gain vs. Frequency
60
50
Voltage Gain, A(Vo/Vin) dB
500
450
400
350
300
250
200
150
100
50
0
Frequency (kHz)
IK - Cathode Current (µA)
LIA120
Cathode Current vs. Photodiode Voltage
90
40
20
0
10
100
1000
Frenquency kHz
*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
Noise Spectrum for 40dB Gain Setup
(220K/2.2K Gain)
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
0
-20
E n ( dB m / H z )
Power (dB)
LIA120
Output Linearity
THD for 40dB Setup
-40
-60
-80
-100
-120
-140
1.000E+02 1.000E+03 1.000E+04 1.000E+05
Frequency (Hz)
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
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5
LIA120
VC
RL
8
100 Ω
+
2
VOUT
7
CC
RC
+
3
6
VOUT
R1
V in
R2
5
–
–
Fig. 6. Power Supply Feedback Application Circuit
VCC
8
2
100 Ω
V DD
R1
7
CC
3
VOUT
RL
6
Ri
RC
5
Vi
R2
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
is typically constrained
R1 by1 the user to
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 KLED
current should be around
3
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
LED and
CTRFB
R1 R
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 CcFor
R1 aR2
the voltage drop of the current limiting resistor
P1
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
V bias
ILED twoout,
by setting
resistors.
The application circuit in
• K1Vout, bias
IRLED
L
Figure 6 shows
a resistor
RL • K1 divider feeding the FB pin, so
the operating conditions
for the gain are governed by:
R1
R1
1
R1
R1
1
R2
K
3
R2
K3
K3 is takenKfrom
the datasheet as 1 nominally. The ac
3
R1
gain of the setupK
can
3
Rbe represented by:
1
VOUT VIN
•
VOUT VIN
m
m
•
m
m
Rev. 2.0
CTRFB R1 R2
CTRFB R1 R2
R1 R2
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 impedance
divider resistor’s
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
R1 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
m
dominant pole Vand
the
VIN linear •optical coupler pole. The
OUT
open loop gain of the optical loop (for the application
diagram) is:
m
Vout, bias
ILED
R1 R2 of R
RL •loop
K1 gain is affected by the selection
The open
1
and R2 and without any compensation
the
circuit
may
RLED Cc R1 R2
R1
R1 of 1a compensation
oscillate.
The addition
networkP(C
1 c
R
K
and
bandwidth so that open
2 Rc) control the maximum
3
loop gain is rolling off long before the optical pole causes
the circuit to oscillate. The optical pole is at ~180kHz so
K3
R1 is typically limited to less than 40kHz.
the bandwidth
While there is flexibility in the part to change the
compensation technique, the upper
limit on frequency
m
VOUT Vis
•
response
IN generally desired to be such that the circuit
will not oscillate for a large selection of R1 and R2.
m capacitor should not be less
Therefore the compensation
than 100pF which gives adequate bandwidth for most
CTRFB R1 through
R2
designs. The bandwidth
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.
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R R
CTRFB R1 R2
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
245ºC 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
PC Board Pattern
(Top View)
8 Pin Surface Mount (“S” Suffix)
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)
AO = 10.30
(0.406)
User Direction of Feed
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
©Copyright 2005, Clare, Inc.
All rights reserved. Printed in USA.
2/17/05