LT4430IS6#PBF Linear Technology, LT4430IS6#PBF Datasheet - Page 17

• Manufacturer Part Number: LT4430IS6#PBF
• Manufacturer: Linear Technology

Specifications of LT4430IS6#PBF

• Operating Temperature (max): 125C
• Operating Temperature (min): -40C
• Pin Count: 6
• Mounting: Surface Mount
• Package Type: TSOT-23
• Case Length: 2.9mm
• Screening Level: Automotive
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS INFORMATION
In this example, the error amplifi er is typically a voltage
error amplifi er confi gured as a transimpedance amplifi er.
The opto-coupler transistor’s emitter provides feedback
information directly to the FB pin and the resistor R
FB to GND sets the DC bias condition for the opto-coupler.
The open loop transfer function from the output voltage
to the primary-side error amplifi er’s output is:
Figure 6b and its transfer function illustrate most of the
possible poles and zeroes that can be set and are shown
for the sake of completeness. In a practical application,
the transfer function simplifi es considerably because not
all the poles and zeroes are used.
In both confi gurations, the terms R
vary from part to part and also change with bias current.
For most opto-couplers, R
and 25Ω at a DC bias of 2mA. CTR is the small signal AC
current transfer ratio. As an example, the Fairchild MOC207
opto-coupler has an AC CTR around 1, even though the
DC CTR is much lower when biased at 1mA or 2mA. Most
opto-coupler data sheets do not specify the terms C
C
measurements.
V
BE
V
OUT
C
and r
=
6
– •
(
[ • •
π
1
s A R
A
•
+
and values must be obtained from empirical
⎛
⎜
⎝
1
s r C
⎛
⎜
⎝
+
• •
R
(
1
1
s
π
1
R
1
+
•
+
• (
2
(
R
(
s R
R
R
C
2
BE
•
K
K
2
⎞
⎟
⎠
+
)
•
+
K
• (
R
•
R R
C
1
•
D
(
D
D
1
C
+
3
)
)
is 50Ω at a DC bias of 1mA,
)]•
+
K
s R C
•
)
s R
•
C
⎛
⎜
⎝
•
K
1
1 1 1
1
⎞
⎟
⎠
D
+
• )• (
C
, CTR, r
•
s R
•
(
CTR R
R
C
•
K
C
3
)
+
π
•
•
+
R
, C
(
(
C
s R
D
C
C
CB
2
•
)
2
•
+
•
and C
3
C
C
E
•
3
3
from
C
)
)
3
⎞
⎟
⎠
CB
BE
)
.
,
•
This frequency compensation discussion only addresses
the transfer function from the output back to the control
node on the primary-side. Compensation of the entire
feedback loop must combine this transfer function with
the transfer function of the power processing circuitry,
commonly referred to as the modulator. In an isolated
power supply, the modulator’s transfer function depends
on topology (fl yback, forward, push-pull, bridge), cur-
rent or voltage mode control, operation in discontinuous
or continuous mode, input/output voltage, transformer
turns ratio and output load current. It is beyond this data
sheet’s scope to detail the transfer functions for all of the
various combinations. However, the power supply designer
must fully characterize and understand the modulator’s
transfer function to successfully frequency compensate
the feedback loop for all operating conditions.
Opto-Couplers
Opto-couplers are available in a wide variety of package
styles and performance criteria including isolation rating,
CTR, output transistor breakdown voltage, output transistor
current capability, and response time. Table 1 lists several
manufacturers of opto-coupler devices, although this is
by no means a complete list.
Table 1. Opto-Coupler Vendors
VENDOR
Agilent Technologies
Fairchild Semiconductor
Isocom
Kodenshi Korea Corp.
NEC
Sharp Microelectronics
Toshiba
Vishay
PHONE
800-235-0312
207-775-8100
214-495-0755
82-63-839-2111
81-44-435-1588
877-343-2181
949-455-2000
402-563-6866
URL
www.agilent.com
www.fairchildsemi.com
www.isocom.com
www.kodenshi.co.kr
www.ncsd.necel.com
www.sharpsma.com
www.toshiba.com
www.vishay.com
LT4430
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