LinkSwitch-4
Family
Energy-Efficient, Accurate Primary-Side Regulated
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
•
Dynamic base drive technology provides flexibility in choice of BJT
~
LinkSwitch-4
U1
LNK4xx2S
CS
GND
BD
ED
VCC
FB
transistor by dynamically optimizing BJT switching characteristics
•
Extends RBSOA of BJT
•
Dramatically reduces sensitivity to BJT gain
Compensates for input line voltage variations
Compensates for cable voltage drop
Compensates for external component temperature variations
Very accurate IC parameter tolerances using proprietary trimming
technology
•
Frequency up to 65 kHz to reduce transformer size
•
The minimum peak current is fixed to improve transient load response
•
•
•
•
Figure 1.
Typical Application (SOT-23-6) (S).
PI-7462-122315
+
BD
ED
Enhanced Performance Features
•
Easy start for starting into capacitive loads (LNK4114D, LNK4115D)
•
Constant power for high current start-up (LNK4214D, LNK4215D)
•
13003 drive improved efficiency with 13003 BJT’s (LNK4302S,
~
LinkSwitch-4
U1
LNK40x3D
CS
GND
VCC
SBD
FB
LNK4322S)
Advanced Protection/Safety Features
•
Single fault output overvoltage and short-circuit
•
Over-temperature protection
•
Active clamp
Figure 2.
Typical Application (SO-8) (D).
PI-7464-010815
EcoSmart™–
Energy Efficient
Output Power Table
85 - 265 VAC
Product
3,4
•
Meets DoE 6 and CoC V5 2016 via an optimized quasi-resonant
switching PWM/PFM control
•
No-load consumption of <30 mW at 230 VAC input
Features
5
13003 Drive
STD
STD
STD
STD
STD
STD
Easy Start
Easy Start + Constant Power
Easy Start
Easy Start + Constant Power
Adapter
1
Open Frame
2
5W
6.5 W
8W
8W
10 W
10 W
15 W
15 W
15 W
18 W
18 W
Green Package
Applications
•
Halogen free and RoHS compliant package
•
Chargers for cell/cordless phones, PDAs, MP3/portable audio
devices, adapters, networking, etc.
Description
The LinkSwitch
TM
-4 family of ICs dramatically simplifies low power CV/CC
charger design by eliminating an optocoupler and secondary control
circuitry. The LinkSwitch-4 family adaptive BJT drive technology uses
combined base and emitter switching to boost switching performance
and deliver higher efficiency, wider Reverse Bias Safe Operating Area
(RBSOA) margin and the flexibility to accommodate a wide range of low
cost BJT. The device incorporates a multimode PWM/PFM controller
with quasi resonant switch to maximize the efficiency, meets low
no-load power and at same time maintain fast transient response
greater than 4.3 V with a load change from 0% to 100%.
LNK43x2S
LNK40x2S
LNK40x3S
LNK4323S
LNK40x3D
LNK4323D
LNK40x4D
LNK4114D
LNK4214D
LNK4115D
LNK4215D
Figure 3.
SOT-23-6 and SO-8 Packages.
Table 1. Output Power Table.
Notes:
1. Minimum continuous power in a typical enclosed adapter measured at +50 °C
ambient, 85-265 VAC device T
J
≤ 100 °C.
2. Maximum practical continuous power in an open frame design with adequate
heat sinking, measured at +50 °C.
3. Package: D: SO-8 , S: SOT-23-6.
4. Cable compensation factor. x = 0 (no cable compensation),
x = 1 (3% cable compensation) x = 2 (6% cable compensation).
5. Easy Start feature uses the BJT current to directly charge C
VCC
, allowing
start-up into large output capacitors. 13003 drive feature has the gate drive
optimized for maximum efficiency when using 13003 BJTs. Constant power
feature provides 175% of rated current at start-up, allowing start-up into
large output capacitors (see Figure 15). STD are standard products with all
the advanced performance and protection/safety features.
May 2018
www.power.com
This Product is Covered by Patents and/or Pending Patent Applications.
LinkSwitch-4
V
DD
V
DD(REG)
V
DD
REGULATOR
VOLTAGE SUPPLY
(VCC)
I
FBHT(LO)
I
FBHT(START)
V
HT
ESTIMATOR
V
IN
UVP
Reset
Signal
RESET CIRCUIT
V
VCC(RUN)
V
VCC(SLEEP)
CYCLE
TIMING
THERMAL
SHUTDOWN
V
OUT
V
OVP
OVP
CABLE
COMPENSATION
EMITTER DRIVE
(ED)
CV VOLTAGE
CONTROL
PFM/PWM
BASE DRIVE
(BD)
FEEDBACK
(FB)
CURRENT
SENSE
(CS)
CC CURRENT
CONTROL
V
CSTHR
CS BLANKING
V
CMAX
OCP
PI-7460-033015
GROUND
(GND)
CS
Figure 4.
LNK40x2S, LNK40x3S, LNK4323S and LNK43x2S Functional Block Diagram.
2
Rev. F 05/18
www.power.com
LinkSwitch-4
V
DD
V
DD(REG)
V
DD
REGULATOR
VOLTAGE SUPPLY
(VCC)
I
FBHT(LO)
I
FBHT(START)
V
HT
ESTIMATOR
V
IN
UVP
Reset
Signal
RESET CIRCUIT
V
VCC(RUN)
V
VCC(SLEEP)
SUPPLEMENTARY
BASE DRIVE
(SBD)
CYCLE
TIMING
THERMAL
SHUTDOWN
V
OUT
V
OVP
OVP
CABLE
COMPENSATION
EMITTER DRIVE
(ED)
CV VOLTAGE
CONTROL
PFM/PWM
SWITCH
BASE DRIVE
(BD)
FEEDBACK
(FB)
CURRENT
SENSE
(CS)
CC CURRENT
CONTROL
V
CSTHR
CS BLANKING
V
CMAX
OCP
PI-7465-033015
GROUND
(GND)
CS
Figure 5.
LNK40x3D, LNK4323D, LNK40x4D, LNK4114D, LNK4115D and LNK4215D Functional Block Diagram.
Pin Functional Description
VOLTAGE SUPPLY (VCC) Pin:
During Run mode, power derived from the transformer voltage
supply winding is fed to the control circuitry via the VOLTAGE
SUPPLY pin.
BASE DRIVE (BD) Pin:
BASE DRIVE pin for BJT.
EMITTER DRIVE (ED) Pin:
D Package (SO-8)
(LNK40x3D, LNK4323D)
CS
VCC
SBD
BD
1
2
3
4
8
7
6
5
FB
GND
GND
ED
S Package (SOT-23-6)
FB
GND
ED
1
2
3
6
5
4
CS
VCC
BD
EMITTER DRIVE pin for BJT.
FEEDBACK (FB) Pin:
The FEEDBACK pin input provides feedback to the control
circuitry by monitoring the transformer voltage waveform.
GROUND (GND) Pin:
D Package (SO-8)
(LNK40x4D, LNK4114D, LNK4214D,
LNK4115D, LNK4215D)
CS
VCC
BD
SBD
1
2
3
4
8
7
6
5
FB
GND
GND
ED
PI-7673-061516
Power and signal ground.
Primary CURRENT SENSE (CS) Pin:
Primary CURRENT SENSE pin via R
CS
.
SUPPLEMENTARY BASE DRIVE (SBD) Pin:
Supplementary base drive.
Figure 6.
Pin Configuration.
3
www.power.com
Rev. F 05/18
LinkSwitch-4
Functional Description
Power-Up/Power-Down Sequences
Refer to Figure 10 and Figure 7. When mains input voltage (V
IN
) is
applied, current flows through the start-up resistors (R
HT
) and BJT.
Some of this current flows into the LinkSwitch-4 internal circuits,
which are in Sleep mode; the remainder charges capacitor C
VCC
.
As soon as the VOLTAGE SUPPLY pin voltage rises to V
VCC(RUN)
, the
LinkSwitch-4 changes to Initialise mode. Current consumption
increases to I
VCC(RUN)
while internal circuits are enabled. The emitter
switch is held at low impedance to ground (GND) and a short drive
pulse is output on the BASE DRIVE pin, during which time the voltage
at feedback is held at GND potential by current sourced from the
FEEDBACK pin. This enables the LinkSwitch-4 control circuit to
compare the rectified mains input voltage with thresholds for allowing
or preventing the next stage of power-up. If the input voltage is too
low (I
FB
< I
FBHT(START)
), the LinkSwitch-4 will not issue further drive
pulses, the VCC voltage will discharge to V
VCC(SLEEP)
, and the power-up
sequence will repeat. If the mains input voltage is high enough (I
FB
>
I
FBHT(START)
), the LinkSwitch-4 will enter Run mode and drive pulses will
be output on the BASE DRIVE pin. To achieve smooth power-up
(monotonic rise in V
OUT
), C
VCC
must be large enough to power the
control circuitry during Initialize mode and the first few cycles of Run
mode, until sufficient power is provided by the transformer voltage
supply winding.
If the input voltage falls below V
MAINS(LO)
(see Input Undervoltage
Protection), V
VCC
will fall below V
VCC(SLEEP)
and the LinkSwitch-4 will go
into Sleep mode, reducing its current consumption to I
VCC(SLEEP)
. The
control circuitry will re-initialize if the input voltage is restored and
V
VCC
reaches V
VCC(RUN)
.
V
VCC(RUN)
V
VCC
V
VCC(SLEEP)
Off
Sleep
Initialize
Run
Sleep
Off
PI-7457-010815
Figure 7.
VCC Waveforms.
Mode
Description
From initial application of input power or from Run mode, if V
VCC
falls below V
VCC(SLEEP)
, the LinkSwitch-4 goes to Sleep mode.
Non-essential circuits are turned off. Base and Emitter drives are turned off so BASE DRIVE and EMITTER DRIVE pins
become high impedance, allowing the bootstrap resistor (R
HT
) and BJT to start the circuit. Sleep mode is exited when V
VCC
rises to V
VCC(RUN)
and the control circuitry goes to Initialize mode.
Internal circuits are enabled and the LinkSwitch-4 issues one switching cycle to sample the input voltage via the FEEDBACK
pin. If V
IN
(hence V
HT
) is high enough, the LinkSwitch-4 changes to Run mode. If V
IN
is not high enough, no further base drive
pulses are issued and the LinkSwitch-4 returns to Sleep mode when V
VCC
falls below V
VCC(SLEEP)
.
Power conversion: The control circuitry is powered from the VCC rail and the internal V
DD
is regulated. If V
VCC
falls below
V
VCC(SLEEP)
, the IC ceases power conversion and goes to Sleep mode.
Summary of LinkSwitch-4 Operating Modes.
Sleep
Initialize
Run
Table 2.
4
Rev. F 05/18
www.power.com
LinkSwitch-4
Switching Waveforms
Typical waveforms at the feedback and primary current sense inputs
are shown in Figure 8.
t
SAMP
FB
V
FBREG
0V
t
CSB
0V
CS
V
CSTHR
t
FON
BD
ED
V
VCC(RUN)
0A
ON
OFF
Transformer
Flux
PI-7458-010815
Figure 8.
Typical Waveforms at the Feedback and Primary Current Sense Inputs.
Constant Voltage (CV) Regulation
Constant output voltage regulation is achieved by sensing the voltage
at the feedback input, which is connected to the voltage supply
winding as shown in Figure 10 or to a dedicated feedback winding.
An internal current source prevents the feedback voltage from going
negative. A typical feedback voltage waveform is shown in Figure 8.
The feedback waveform is continuously analyzed and sampled at time
t
SAMP
to measure the reflected output voltage. t
SAMP
is identified by the
slope of the feedback waveform and is coincident with zero flux in the
transformer. The sampled voltage is regulated at V
FB(REG)
by the
voltage control loop. The (typical) CV mode output voltage is set by
the ratio of resistors R
FB1
and R
FB2
(see Figure 10) and by the
transformer turns ratio, according to the following formula (where
output diode voltage is neglected):
approximate mains input voltage. If the input voltage is below
V
MAINS(START)
then the LinkSwitch-4 will not start. Instead it will pause
while V
VCC
discharges below V
VCC(SLEEP)
then it will begin a new power-up
cycle. If the input voltage exceeds V
MAINS(START)
, the converter will
power-up. V
MAINS(START)
is set by R
FB1
using this equation:
V
MAINS
^
START
h
=
N
-1
#
I
FBHT
^
START
h
#
R
FB
1
#
N
P
F
2
Input Undervoltage Protection
In Run mode, if the mains voltage falls to V
MAINS(LO)
, the LinkSwitch-4
will stop issuing drive pulses, V
VCC
will reduce to V
VCC(SLEEP)
and the
LinkSwitch-4 will enter Sleep mode. V
MAINS(LO)
is set by R
FB1
using this
equation:
N
R
V
OUT
^
CV
h
=
V
FB
^
REG
h
a
1 +
R
FB
1
k
a
N
S
k
FB
2
F
Where N
F
is the number of turns on the feedback (or voltage supply
if used for feedback) winding and N
S
is the number of turns on the
secondary winding. The tolerances of R
FB1
and R
FB2
affect output
voltage regulation and mains estimation so should typically be chosen
to be 1% or better.
The current required to clamp the feedback voltage to ground
potential during the on-time of the primary switch depends on the
primary winding voltage (approximately equal to the rectified mains
input voltage), the primary to feedback turns ratio, and resistor R
FB1
.
The controller measures feedback source current and so enables R
FB1
to set the input voltage start threshold and the input undervoltage
protection threshold, as described below.
Input Voltage Start Threshold
In Initialise mode, the LinkSwitch-4 issues a single short-duration
drive pulse in order to measure the primary voltage and so the
V
MAINS
^
LO
h
=
N
-1
#
I
FBHT
^
LO
h
#
R
FB
1
#
N
P
F
2
Constant Current (CC Mode) Regulation
Constant current output (I
OUT(CC)
) is achieved by regulating the CS
input to the primary side estimate of the output current scaled by R
CS,
V
CS(CC)
. The regulated output current, I
OUT(CC)
is set by the value of the
current sense resistor, R
CS
, and the transformer primary to secondary
turns ratio (N
P
/N
S
). The value of R
CS
is determined using the formula:
V
CS
^
CC
h
^
Typ
h
N
n
R
CS
.
a
N
P
k
d
S
I
OUT
^
CC
h
^
Typ
h
The tolerance of R
CS
affects the accuracy of output the current
regulation so is typically chosen to be 1%. The LinkSwitch-4 can
maintain CC regulation down to much lower levels of V
SHUTDN(MAX)
normally specified for mobile phones chargers (see Figure 11).
5
www.power.com
Rev. F 05/18
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