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 trans-
former size
Wide Range
High-Voltage
DC Input
LinkSwitch-II
D
FB
BP/M
S
PI-4960-012315
(a) Typical Application Schematic
V
O
±5%
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
±10%
EcoSmart
™
– Energy Efficient
PI-4906-012315
•
Easily meets all global energy efficiency regulations
•
No-load consumption below 30 mW at 230 VAC with optional
(b) Output Characteristic
Figure 1.
I
O
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
Typical Application/Performance – Not a Simplified Circuit (a) and
Output Characteristic Envelope (b). (see Application Section for
more information).
Green Package
Applications
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
•
Halogen free and RoHS compliant package
•
Chargers for cell/cordless phones, PDAs, MP3/portable audio
devices, adapters, LED drivers, etc.
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.
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 Consider-
ations section for more information).
3. Packages: P: DIP-8C, G: SMD-8C, D: SO-8C.
DIP-8C (P Package)
Figure 2.
www.power.com
SMD-8C (G Package)
SO-8C (D Package).
Package Options.
August 2016
This Product is Covered by Patents and/or Pending Patent Applications.
LNK603-606/613-616
BYPASS
(BP/M)
FB
OUT
6V
5V
REGULATOR
6V
+
+
DRAIN
(D)
FEEDBACK
(FB)
V
TH
-
D
Q
STATE
MACHINE
I
LIM
Reset
V
ILIMIT
Drive
-
t
SAMPLE-OUT
CABLE DROP
COMPENSATION
6.5 V
INDUCTANCE
CORRECTION
V
ILIMIT
DC
MAX
FAULT
Auto-Restart
Open-Loop
THERMAL
SHUTDOWN
t
SAMPLE-OUT
t
SAMPLE-INPUT
OSCILLATOR
+
FB
t
SAMPLE-INPUT
DC
MAX
SAMPLE
DELAY
SOURCE
(S)
CONSTANT
CURRENT
I
LIM
SOURCE
(S)
V
ILIMIT
LEADING
EDGE
BLANKING
-
Current Limit
Comparator
PI-4908-012915
Figure 3.
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:
P Package (DIP-8C)
G Package (SMD-8C)
FB
BP/M
1
2
8
7
6
D
4
5
S
S
S
S
D Package (SO-8C)
1
2
8
7
6
D
4
5
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.
FB
BP/M
S
S
S
S
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.
PI-3491-020615
Figure 4.
Pin Configuration.
2
Rev. J 08/16
www.power.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.power.com
Rev. J 08/16
LNK603-606/613-616
Applications Example
C6
R7
1 nF
100 V 200
Ω
L1
1.5 mH
R2
470 kΩ
C3
820 pF
1 kV
5
T1
EE16
10
5 V, 555 mA
D7
SS14
C7
680
µF
10 V
D1
1N4007
RF1
8.2
Ω
2W
D2
1N4007
3
8
1
R8
200
Ω
DC
Output
R3
300
Ω
D5
1N4007
2
VR1
2MM5230B-7
4.7 V
AC
Input
C1
4.7
µF
400 V
C2
4.7
µF
400 V
4
NC
D3
1N4007
D4
1N4007
LinkSwitch-II
U1
LNK613DG
D
D6
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-5111-012315
Figure 5.
Energy Efficient USB Charger Power Supply (74% Average Efficiency, <30 mW No-load Input Power).
Circuit Description
This circuit shown in Figure 5 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 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 and
Microcontroller MCU
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