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LNK302D 데이터시트 PDF : 부품 기능 및 핀배열

부품번호 LNK302D
기능 Energy-Efficient Off-Line Switcher IC
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LNK302D 데이터시트 및 LNK302D PDF

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LNK302D pdf, 반도체, 판매, 대치품
LNK302/304-306
600
500
VDRAIN
400
300
200
100
0
68 kHz
64 kHz
0
Figure 4. Frequency Jitter.
Time (µs)
20
Auto-Restart (LNK304-306 Only)
In the event of a fault condition such as output overload, output
short, or an open-loop condition, LinkSwitch-TN enters into
auto-restart operation. An internal counter clocked by the
oscillator gets reset every time the FEEDBACK pin is pulled
high. If the FEEDBACK pin is not pulled high for 50 ms, the
power MOSFET switching is disabled for 800 ms. The auto-
restart alternately enables and disables the switching of the
power MOSFET until the fault condition is removed.
Applications Example
A 1.44 W Universal Input Buck Converter
The circuit shown in Figure 5 is a typical implementation of a
12 V, 120 mA non-isolated power supply used in appliance
control such as rice cookers, dishwashers or other white goods.
This circuit may also be applicable to other applications such as
night-lights, LED drivers, electricity meters, and residential
heating controllers, where a non-isolated supply is acceptable.
The input stage comprises fusible resistor RF1, diodes D3 and
D4, capacitors C4 and C5, and inductor L2. Resistor RF1 is a
flame proof, fusible, wire wound resistor. It accomplishes
several functions: a) Inrush current limitation to safe levels for
rectifiers D3 and D4; b) Differential mode noise attenuation; c)
Input fuse should any other component fail short-circuit
(component fails safely open-circuit without emitting smoke, fire
or incandescent material).
The power processing stage is formed by the LinkSwitch-TN,
freewheeling diode D1, output choke L1, and the output capacitor
C2. The LNK304 was selected such that the power supply
operates in the mostly discontinuous-mode (MDCM). Diode D1
is an ultrafast diode with a reverse recovery
approximately 75 ns, acceptable for MDCM
toimpeera(ttRiRo)no.f
For
continuous
of 35 ns is
conduction mode (CCM) designs, a diode
recommended. Inductor L1 is a standard
wofift-hthaet-rr
shelf inductor with appropriate RMS current rating (and acceptable
temperature rise). Capacitor C2 is the output filter capacitor; its
primary function is to limit the output voltage ripple. The output
voltage ripple is a stronger function of the ESR of the output
capacitor than the value of the capacitor itself.
To a first order, the forward voltage drops of D1 and D2 are
identical. Therefore, the voltage across C3 tracks the output
voltage. The voltage developed across C3 is sensed and
regulated via the resistor divider R1 and R3 connected to U1’s
FEEDBACK pin. The values of R1 and R3 are selected such
that, at the desired output voltage, the voltage at the
FEEDBACK pin is 1.65 V.
Regulation is maintained by skipping switching cycles. As the
output voltage rises, the current into the FEEDBACK pin will
rureisndetiu.l cthIefedth,cismureorexrecnetceryedcdsleuIscFBewtshilelbbneelsouswkbiIspFeBp.qeuTdehanuntsdc, yaicfsltehthseewlooialludbtpeinusctkrleoipaapsdeeidss,
fewer cycles are skipped. To provide overload protection if no
cycles are skipped during a 50 ms period, LinkSwitch-TN will
enter auto-restart (LNK304-306), limiting the average output
power to approximately 6% of the maximum overload power.
Due to tracking errors between the output voltage and the
voltage across C3 at light load or no-load, a small pre-load may
be required (R4). For the design in Figure 5, if regulation to zero
load is required, then this value should be reduced to 2.4 k.
RF1
8.2
2W
85-265
VAC
D3
1N4007
D4
1N4007
L2
1 mH
C4
4.7 µF
400 V
R1
13.0 k
1%
FB
D
C5
4.7 µF
400 V
BP
C1
100 nF
S
LinkSwitch-TN
LNK304
R3
2.05 k
1%
D1
UF4005
C3
10 µF
35 V
L1
1 mH
280 mA
D2
1N4005GP
C2
100 µF
16 V
R4
3.3 k
Figure 5. Universal Input, 12 V, 120 mA Constant Voltage Power Supply Using LinkSwitch-TN.
12 V,
120 mA
RTN
PI-3757-041509
4
Rev. J 06/13
www.powerint.com

4페이지

LNK302D 전자부품, 판매, 대치품
LNK302/304-306
Topology
Low-Side
Buck-Boost –
Optocoupler
Feedback
+
VIN
Basic Circuit Schematic
LinkSwitch-TN
BP FB
SD
VO
+
PI-3756-041509
Key Features
1. Output referenced to input
2.
3.
4.
PSOotpestpoiticuvoepu/odpuoletwpr unfet–e(VdVObO)aw>ckitVhINreosr pVeOc<t
tVoIN+VIN
- Accuracy only limited by reference choice
- Low cost non-safety rated optocoupler
- No pre-load required
5. Fail-safe – output is not subjected to input
voltage if the internal power MOSFET fails
6. Minimum no-load consumption
Table 2 (cont). Common Circuit Configurations Using LinkSwitch-TN.
Component Selection
Referring to Figure 5, the following considerations may be
helpful in selecting components for a LinkSwitch-TN design.
Freewheeling Diode D1
Diode D1 should be an ultrafast type. For MDCM, reverse
r7e0c°oCveorrybteimloewt.RRSlo7w5enr sdisohdoeusldarbeenoutseacdcaetpatatbelme,paesrcaotunrteinoufous
mode operation will always occur during startup, causing high
leading edge current spikes, terminating the switching cycle
prematurely, and preventing the output from reaching regulation.
If the ambient temperature is above 70 °C then a diode with tRR
35 ns should be used.
For CCM an ultrafast diode with reverse recovery time tRR 35 ns
should be used. A slower diode may cause excessive leading
edge current spikes, terminating the switching cycle prematurely
and preventing full power delivery.
Fast and slow diodes should never be used as the large reverse
recovery currents can cause excessive power dissipation in the
diode and/or exceed the maximum drain current specification
of LinkSwitch-TN.
Feedback Diode D2
Diode D2 can be a low-cost slow diode such as the 1N400X
series, however it should be specified as a glass passivated
type to guarantee a specified reverse recovery time. To a first
order, the forward drops of D1 and D2 should match.
Inductor L1
Choose any standard off-the-shelf inductor that meets the
design requirements. A “drum” or “dog bone” “I” core inductor
is recommended with a single ferrite element due to its low cost
and very low audible noise properties. The typical inductance
value and RMS current rating can be obtained from the
LinkSwitch-TN design spreadsheet available within the PI Expert
design suite from Power Integrations. Choose L1 greater than
or equal to the typical calculated inductance with RMS current
rating greater than or equal to calculated RMS inductor current.
Capacitor C2
The primary function of capacitor C2 is to smooth the inductor
current. The actual output ripple voltage is a function of this
capacitor’s ESR. To a first order, the ESR of this capacitor
should not exceed the rated ripple voltage divided by the typical
current limit of the chosen LinkSwitch-TN.
Feedback Resistors R1 and R3
The values of the resistors in the resistor divider formed by R1
and R3 are selected to maintain 1.65 V at the FEEDBACK pin. It
is recommended that R3 be chosen as a standard 1% resistor
of 2 k. This ensures good noise immunity by biasing the
feedback network with a current of approximately 0.8 mA.
Feedback Capacitor C3
Capacitor C3 can be a low cost general purpose capacitor. It
provides a “sample and hold” function, charging to the output
voltage during the off time of LinkSwitch-TN. Its value should
be 10 µF to 22 µF; smaller values cause poorer regulation at
light load conditions.
Pre-Load Resistor R4
In high-side, direct feedback designs where the minimum load
is <3 mA, a pre-load resistor is required to maintain output
regulation. This ensures sufficient inductor energy to pull the
inductor side of the feedback capacitor C3 to input return via
D2. The value of R4 should be selected to give a minimum
output load of 3 mA.
In designs with an optocoupler the Zener or reference bias
current provides a 1 mA to 2 mA minimum load, preventing
“pulse bunching” and increased output ripple at zero load.
LinkSwitch-TN Layout Considerations
In the buck or buck-boost converter configuration, since the
SOURCE pins in LinkSwitch-TN are switching nodes, the
copper area connected to SOURCE should be minimized to
minimize EMI within the thermal constraints of the design.
In the boost configuration, since the SOURCE pins are tied to
DC return, the copper area connected to SOURCE can be
maximized to improve heat sinking.
The loop formed between the LinkSwitch-TN, inductor (L1),
freewheeling diode (D1), and output capacitor (C2) should be
kept as small as possible. The BYPASS pin capacitor C1
(Figure 6) should be located physically close to the SOURCE (S)
and BYPASS (BP) pins. To minimize direct coupling from
switching nodes, the LinkSwitch-TN should be placed away
www.powerint.com
7
Rev. J 06/13

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