LNK603-606/613-616
™
LinkSwitch-II
Family
Energy-Efficient, Accurate CV/CC Switcher
for Adapters and Chargers
Product Highlights
Dramatically Simplifies CV/CC Converters
•
Eliminates optocoupler and all secondary CV/CC control circuitry
•
Eliminates all control loop compensation circuitry
Advanced Performance Features
•
Compensates for transformer inductance tolerances
•
Compensates for input line voltage variations
•
Compensates for cable voltage drop (LNK61X series)
•
Compensates for external component temperature variations
•
Very tight IC parameter tolerances using proprietary trimming
technology
•
Frequency jittering greatly reduces EMI filter cost
•
Even tighter output tolerances achievable with external resistor
selection/trimming
•
Programmable switching frequency up to 85 kHz to reduce
transformer size
Advanced Protection/Safety Features
•
Auto-restart protection reduces power delivered by >95% for
output short-circuit and control loop faults (open and shorted
components)
•
Hysteretic thermal shutdown – automatic recovery reduces
power supply returns from the field
•
Meets high-voltage creepage requirements between DRAIN
and all other pins both on the PCB and at the package
EcoSmart
™
– Energy Efficient
•
Easily meets all global energy efficiency regulations
•
No-load consumption below 30 mW at 230 VAC with optional
external bias winding
•
ON/OFF control provides constant efficiency down to very light
loads – ideal for CEC and ENERGY STAR 2.0 regulations
•
No current sense resistors – maximizes efficiency
Green Package
•
Halogen free and RoHS compliant package
Applications
•
Chargers for cell/cordless phones, PDAs, MP3/portable audio
devices, adapters, LED drivers, etc.
Figure 1.
Wide Range
High-Voltage
DC Input
LinkSwitch-II
S
D
FB
BP/M
PI-4960-011510
(a) Typical Application Schematic
V
O
±5%
±10%
PI-4906-041008
(b) Output Characteristic
I
O
Typical Application/Performance – Not a Simplified Circuit (a) and
Output Characteristic Envelope (b). (see Application Section for
more information).
Output Power Table
Product
3
LNK603/613PG/DG
LNK604/614PG/DG
LNK605/615PG/DG
LNK606/616PG/GG/DG
85-265 VAC
Adapter
1
2.5 W
3.5 W
4.5 W
5.5 W
Open Frame
2
3.3 W
4.1 W
5.1 W
6.1 W
Description
The LinkSwitch-II dramatically simplifies low power CV/CC
charger designs by eliminating an optocoupler and secondary
control circuitry. The device introduces a revolutionary control
technique to provide very tight output voltage and current
regulation, compensating for transformer and internal parameter
tolerances along with input voltage variations.
The device incorporates a 700 V power MOSFET, a novel ON/OFF
control state machine, a high-voltage switched current source for
self biasing, frequency jittering, cycle-by-cycle current limit and
hysteretic thermal shutdown circuitry onto a monolithic IC.
www.powerint.com
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical non-ventilated enclosed adapter
measured at +50 °C ambient, device, T
J
<100 °C.
2. Maximum practical continuous power in an open frame design with adequate
heat sinking, measured at 50 °C ambient (see Key Applications Considerations
section for more information).
3. Packages: P: DIP-8C, G: SMD-8C, D: SO-8C.
March 2014
This Product is Covered by Patents and/or Pending Patent Applications.
LNK603-606/613-616
BYPASS
(BP/M)
+
-
REGULATOR
6V
FB
OUT
6V
5V
+
-
DRAIN
(D)
FEEDBACK
(FB)
V
TH
D
STATE
MAC INE
I
LIM
Reset
V
ILIMIT
Drive
t
SAMPLE-OUT
CABLE DROP
COMPENSATION
V
ILIMIT
DC
MAX
FAULT
-R
-L
6.5 V
INDUCTANCE
CORRECTION
FB
A
O
t
SAMPLE-INPUT
DC
MAX
T ERMAL
S UTDO N
t
SAMPLE-INPUT
OSCILLATOR
t
SAMPLE-OUT
SAMPLE
DELAY
SOURCE
(S)
CONSTANT
CURRENT
I
LIM
+
-
V
ILIMIT
LEADING
EDGE
BLANKING
SOURCE
(S)
Current Limit
Comparator
PI-4908-041508
Figure 2.
Functional Block Diagram.
Pin Functional Description
DRAIN (D) Pin:
This pin is the power MOSFET drain connection. It provides
internal operating current for both start-up and steady-state
operation.
BYPASS/MULTI-FUNCTIONAL PROGRAMMABLE (BP/M) Pin:
This pin has multiple functions:
1. It is the connection point for an external bypass capacitor for
the internally generated 6 V supply.
2. It is a mode selection for the cable drop compensation for
LNK61X series.
FEEDBACK (FB) Pin:
During normal operation, switching of the power MOSFET is
controlled by this pin. This pin senses the AC voltage on the bias
winding. This control input regulates both the output voltage in
CV mode and output current in CC mode based on the flyback
voltage of the bias winding. The internal inductance correction
circuit uses the forward voltage on the bias winding to sense the
bulk capacitor voltage.
SOURCE (S) Pin:
This pin is internally connected to the output MOSFET source for
high-voltage power and control circuit common returns.
P Package (DIP-8C)
G Package (SMD-8C)
FB
BP/M
1
2
8
7
6
D
4
3a
D Package (SO-8C)
1
2
8
7
6
D
4
3b
S
S
S
S
FB
BP/M
S
S
S
S
5
5
PI-3491-092010
Figure 3.
Pin Configuration.
2
Rev. H 03/14
www.powerint.com
LNK603-606/613-616
LinkSwitch-II Functional Description
The LinkSwitch-II combines a high-voltage power MOSFET
switch with a power supply controller in one device. Similar to
the LinkSwitch-LP and TinySwitch-III it uses ON/OFF control to
regulate the output voltage. In addition, the switching frequency
is modulated to regulate the output current to provide a
constant current characteristic. The LinkSwitch-II controller
consists of an oscillator, feedback (sense and logic) circuit, 6 V
regulator, over-temperature protection, frequency jittering,
current limit circuit, leading-edge blanking, inductance
correction circuitry, frequency control for constant current
regulation and ON/OFF state machine for CV control.
Inductance Correction Circuitry
If the primary magnetizing inductance is either too high or low
the converter will automatically compensate for this by adjusting
the oscillator frequency. Since this controller is designed to
operate in discontinuous-conduction mode the output power is
directly proportional to the set primary inductance and its
tolerance can be completely compensated with adjustments to
the switching frequency.
Constant Current (CC) Operation
As the output voltage and therefore the flyback voltage across
the bias winding increases, the FEEDBACK pin voltage increases.
The switching frequency is adjusted as the FEEDBACK pin
voltage increases to provide a constant output current regulation.
The constant current circuit and the inductance correction
circuit are designed to operate concurrently in the CC region.
Constant Voltage (CV) Operation
As the FEEDBACK pin approaches V
FBth
from the constant
current regulation mode, the power supply transitions into CV
operation. The switching frequency at this point is at its
maximum value, corresponding to the peak power point of the
CC/CV characteristic. The controller regulates the FEEDBACK
pin voltage to remain at V
FBth
using an ON/OFF state-machine.
The FEEDBACK pin voltage is sampled 2.5
ms
after the turn-off
of the high-voltage switch. At light loads the current limit is also
reduced to decrease the transformer flux density.
Output Cable Compensation
This compensation provides a constant output voltage at the
end of the cable over the entire load range in CV mode. As the
converter load increases from no-load to the peak power point
(transition point between CV and CC) the voltage drop introduced
across the output cable is compensated by increasing the
FEEDBACK pin reference voltage. The controller determines the
output load and therefore the correct degree of compensation
based on the output of the state machine. Cable drop
compensation for a 24 AWG (0.3
W)
cable is selected with
C
BP
= 1
mF
and for a 26 AWG (0.49
W)
cable with C
PB
= 10
mF.
Auto-Restart and Open-Loop Protection
In the event of a fault condition such as an output short or an
open loop condition the LinkSwitch-II enters into an appropriate
protection mode as described below.
In the event the FEEDBACK pin voltage during the flyback
period falls below 0.7 V before the FEEDBACK pin sampling
delay (~2.5
ms)
for a duration in excess of ~450 ms (auto-restart
on-time (t
AR-ON
) the converter enters into auto-restart, wherein
the power MOSFET is disabled for 2 seconds (~18% auto-
restart duty cycle). The auto-restart alternately enables and
disables the switching of the power MOSFET until the fault
condition is removed.
In addition to the conditions for auto-restart described above, if
the sensed FEEDBACK pin current during the forward period of
the conduction cycle (switch “on” time) falls below 120
mA,
the
converter annunciates this as an open-loop condition (top
resistor in potential divider is open or missing) and reduces the
auto-restart time from 450 ms to approximately 6 clock cycles
(90
ms),
whilst keeping the disable period of 2 seconds.
Over-Temperature Protection
The thermal shutdown circuitry senses the die temperature. The
threshold is set at 142 °C typical with a 60 °C hysteresis. When
the die temperature rises above this threshold (142 °C) the
power MOSFET is disabled and remains disabled until the die
temperature falls by 60 °C, at which point the MOSFET is
re-enabled.
Current Limit
The current limit circuit senses the current in the power
MOSFET. When this current exceeds the internal threshold
(I
LIMIT
), the power MOSFET is turned off for the remainder of that
cycle. The leading edge blanking circuit inhibits the current limit
comparator for a short time (t
LEB
) after the power MOSFET is
turned on. This leading edge blanking time has been set so that
current spikes caused by capacitance and rectifier reverse
recovery time will not cause premature termination of the MOSFET
conduction. The LinkSwitch-II also contains a “di/dt” correction
feature to minimize CC variation across the input line range.
6.0 V Regulator
The 6 V regulator charges the bypass capacitor connected to
the BYPASS pin to 6 V by drawing a current from the voltage on
the DRAIN, whenever the MOSFET is off. The BYPASS pin is
the internal supply voltage node. When the MOSFET is on, the
device runs off of the energy stored in the bypass capacitor.
Extremely low power consumption of the internal circuitry
allows the LinkSwitch-II to operate continuously from the
current drawn from the DRAIN pin. A bypass capacitor value of
either 1
mF
or 10
mF
is sufficient for both high frequency
decoupling and energy storage.
3
www.powerint.com
Rev. H 03/14
LNK603-606/613-616
Applications Example
C6
R7
1 nF
100 V 200
Ω
L1
1.5 mH
R2
470 kΩ
D1
1N4007
RF1
8.2
Ω
2W
C1
4.7
µF
400 V
C2
4.7
µF
400 V
D2
1N4007
R3
300
Ω
5
C3
820 pF 3
1 kV
T1
EE16
10
D7
SS14
C7
680
µF
10 V
R8
200
Ω
DC
Output
VR1
2MM5230B-7
4.7 V
5 V, 555 mA
8
1
2
AC
Input
D5
1N4007
4
D3
1N4007
D4
1N4007
D
NC
LinkSwitch-II
D6
U1
LNK613DG LL4148
FB
BP
R5
13 kΩ
1%
S
C4
1
µF
25 V
R4
6.2 kΩ C5
10
µF
16 V
R6
8.87 kΩ
1%
PI-5111-050808
Figure 4.
Energy Efficient USB Charger Power Supply (74% Average Efficiency, <30 mW No-load Input Power).
Circuit Description
This circuit shown in Figure 4 is configured as a primary-side
regulated flyback power supply utilizing the LNK613DG. With
an average efficiency of 74% and <30 mW no-load input power
this design easily exceeds the most stringent current energy
efficiency requirements.
Input Filter
AC input power is rectified by diodes D1 through D4. The
rectified DC is filtered by the bulk storage capacitors C1 and
C2. Inductor L1, C1 and C2 form a pi (π) filter, which attenuates
conducted differential-mode EMI noise. This configuration
along with Power Integrations transformer E-shield
™
technology
allow this design to meet EMI standard EN55022 class B with
good margin without requiring a Y capacitor, even with the
output connected to safety earth ground. Fusible resistor RF1
provides protection against catastrophic failure. This should be
suitably rated (typically a wire wound type) to withstand the
instantaneous dissipation while the input capacitors charge
when first connected to the AC line.
LNK 613 Primary
The LNK613DG device (U1) incorporates the power switching
device, oscillator, CC/CV control engine, startup, and protection
functions. The integrated 700 V MOSFET provides a large drain
voltage margin in universal input AC applications, increasing
reliability and also reducing the output diode voltage stress by
allowing a greater transformer turns ratio. The device is
completely self-powered from the BYPASS pin and decoupling
capacitor C4. For the LNK61X devices, the bypass capacitor
value also selects the amount of output cable voltage drop
4
Rev. H 03/14
compensation. A 1
mF
value selects the standard compensation.
A 10
mF
value selects the enhanced compensation. Table 2
shows the amount of compensation for each device and
bypass capacitor value. The LNK60x devices do not provide
cable drop compensation.
The optional bias supply formed by D6 and C5 provides the
operating current for U1 via resistor R4. This reduces the
no-load consumption from ~200 mW to <30 mW and also
increases light load efficiency.
The rectified and filtered input voltage is applied to one side of
the primary winding of T1. The other side of the transformer’s
primary winding is driven by the integrated MOSFET in U1. The
leakage inductance drain voltage spike is limited by an RCD-R
clamp consisting of D5, R2, R3, and C3.
Output Rectification
The secondary of the transformer is rectified by D7, a 1 A, 40 V
Schottky barrier type for higher efficiency, and filtered by C7. If
lower efficiency is acceptable then this can be replaced with a
1 A PN junction diode for lower cost. In this application C7 was
sized to meet the required output voltage ripple specification
without requiring a post LC filter. To meet battery self discharge
requirement the pre-load resistor has been replaced with a
series resistor and Zener network (R8 and VR1). However in
designs where this is not a requirement a standard 1 kW resistor
can be used.
Output Regulation
The LNK613 regulates the output using ON/OFF control in the
constant voltage (CV) regulation region of the output character-istic
www.powerint.com
LNK603-606/613-616
and frequency control for constant current (CC) regulation. The
feedback resistors (R5 and R6) were selected using standard
1% resistor values to center both the nominal output voltage
and constant current regulation thresholds.
LinkSwitch-II Output Cable Voltage Drop Compensation
Device
LNK613
LNK614
LNK615
LNK616
BYPASS Pin
Capacitor Value
1
mF
10
mF
1
mF
10
mF
1
mF
10
mF
1
mF
10
mF
Output Voltage
Change Factor
1.035
1.055
1.045
1.065
1.050
1.070
1.060
1.090
Key Application Considerations
Output Power Table
The data sheet maximum output power table (Table 1) repre-
sents the maximum practical continuous output power level
that can be obtained under the following assumed conditions:
1. The minimum DC input voltage is 90 V or higher at 85 VAC
input. The value of the input capacitance should be large
enough to meet these criteria for AC input designs.
2. Secondary output of 5 V with a Schottky rectifier diode.
3. Assumed efficiency of 70%.
4. Discontinuous mode operation (K
P
>1.3).
5. The part is board mounted with SOURCE pins soldered to a
sufficient area of copper to keep the SOURCE pin tempera-
ture at or below 90 °C.
6. Ambient temperature of 50 °C for open frame designs and
an internal enclosure temperature of 60 °C for adapter
designs.
Note: Higher output power are achievable if an output CC
tolerance >±10% is acceptable, allowing the device to be
operated at a higher SOURCE pin temperature.
Output Tolerance
LinkSwitch-II provides an overall output tolerance (including line,
component variation and temperature) of ±5% for the output
voltage in CV operation and ±10% for the output current during
CC operation over a junction temperature range of 0 °C to 100 °C
for the P/G package. For the D package (SO8) additional CC
variance may occur due to stress caused by the manufacturing
flow (i.e. solder-wave immersion or IR reflow). A sample power
supply build is recommended to verify production tolerances for
each design.
BYPASS Pin Capacitor Selection
For LinkSwitch-II 60x Family of Devices (without output
cable voltage drop compensation)
A 1
mF
BYPASS pin capacitor is recommended. The capacitor
voltage rating should be greater than 7 V. The capacitor’s
dielectric material is not important but tolerance of capacitor
should be ≤ ±50%. The capacitor must be physically located
close to the LinkSwitch-II BYPASS pin.
For LinkSwitch-II 61x Family of Devices (with output cable
voltage drop compensation)
The amount of output cable compensation can be selected with
the value of the BYPASS pin capacitor. A value of 1
mF
selects
the standard cable compensation. A 10
mF
capacitor selects
the enhanced cable compensation. Table 2 shows the amount
of compensation for each LinkSwitch-II device and capacitor
value. The capacitor can be either ceramic or electrolytic but
tolerance and temperature variation should be ≤ ±50%.
Table 2.
Cable Compensation Change Factor vs. Device and BYPASS Pin
Capacitor Value.
The output voltage that is entered into PIXls design spreadsheet
is the voltage at the end of the output cable when the power
supply is delivering maximum power. The output voltage at the
terminals of the supply is the value measured at the end of the
cable multiplied by the output voltage change factor.
LinkSwitch-II Layout Considerations
Circuit Board Layout
LinkSwitch-II is a highly integrated power supply solution that
integrates on a single die, both, the controller and the high-
voltage MOSFET. The presence of high switching currents and
voltages together with analog signals makes it especially
important to follow good PCB design practice to ensure stable
and trouble free operation of the power supply. See Figure 5 for
a recommended circuit board layout for LinkSwitch-II.
When designing a printed circuit board for the LinkSwitch-II
based power supply, it is important to follow the following
guidelines:
Single Point Grounding
Use a single point (Kelvin) connection at the negative terminal of
the input filter capacitor for the LinkSwitch-II SOURCE pin and
bias winding return. This improves surge capabilities by
returning surge currents from the bias winding directly to the
input filter capacitor.
Bypass Capacitor
The BYPASS pin capacitor should be located as close as
possible to the SOURCE and BYPASS pins.
Feedback Resistors
Place the feedback resistors directly at the FEEDBACK pin of
the LinkSwitch-II device. This minimizes noise coupling.
Thermal Considerations
The copper area connected to the SOURCE pins provides the
LinkSwitch-II heat sink. A good estimate is that the LinkSwitch-II
will dissipate 10% of the output power. Provide enough copper
area to keep the SOURCE pin temperature below 90 °C. Higher
temperatures are allowable only if an output current (CC)
tolerance above ±10% is acceptable. In this case a maximum
SOURCE pin temperature below 110 °C is recommended to
provide margin for part to part R
DS(ON)
variation.
5
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Rev. H 03/14
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