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Power integrations LinkSwitch-4 LNK4*15D Series Application Note

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Application Note AN-69
LinkSwitch-4 Family
Design Guide and Considerations
Introduction
The LinkSwitch™-4 family of ICs dramatically simplifies low power
CV/CC charger/adapter 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 switching to maximize the efficiency,
meets <30 mW no-load and at same time maintains fast transient
response greater than 4.3 V with a load change from 0% to 100%.
Advanced Performance Features
Dynamic base drive technology provides flexibility in choice of BJT
•
transistor by dynamically optimizing BJT switching characteristics
Extends RBSOA of BJT
•
Dramatically reduces sensitivity to BJT gain
•
Compensates for transformer inductance tolerances
•
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
Advanced Protection/Safety Features
Single fault output overvoltage and short-circuit
•
Over-temperature protection
•
EcoSmart™ – Energy Efficient
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
•
Green Package
Halogen free and RoHS compliant package
•
Applications
Chargers for cell/cordless phones, PDAs, MP3/portable audio
•
devices, adapters, etc.
LinkSwitch-4 Family
There are four main family groups covering a power range of nominally
2 W to 18 W and they come in either a SOT23-6 or SO-8 package.
Groups are further subdivided by cable drop compensation levels of
0%, 3% and 6%.
LNK43xxx and LNK4x15D devices have an enhanced base drive
optimization for reduced BJT losses. For example, the LNK4322S can
output 5 W using a TO92 13003 BJT instead of a TO251 13005 and
remain thermally safe. The LNK43x3 devices also include a debounce
delay after a low output voltage is detected to prevent false UVP
foldback being triggered in noisy environments.
www.power.com
Output Power Table
Product
3,4
Features
LNK43x2S
13003 Drive
LNK40x2S
STD
LNK40x3S
STD
LNK4323S
STD
LNK40x3D
STD
LNK4323D
STD
LNK40x4D
STD
LNK4114D
Easy Start
LNK4214D
Easy Start + Constant Power
LNK4115D
Easy Start
LNK4215D
Easy Start + Constant Power
Table 1.
LinkSwtich-4 Selection Table Based on Output Power.
D Package (SO-8)
(LNK40x3D, LNK4323D)
1
CS
2
VCC
3
SBD
4
BD
D Package (SO-8)
(LNK40x4D, LNK4114D, LNK4214D,
LNK4115D, LNK4215D)
1
CS
2
VCC
3
BD
4
SBD
Figure 1.
LinkSwitch-4 Packages.
Note that the LNK4xx3D and LNK4xx4D SO-8 packages have the
SUPPLEMENTARY BASE DRIVE (SBD) pin and BASE DRIVE (BD) pins
swapped. This is to avoid problems with charger/adapter reliability.
The 10 W rated LNK40X3D would otherwise work in a 15 W LNK40X4D
design and may pass production final test, but it would be over-
stressed and probably result in field failures.
85 - 265 VAC
Adapter
5
Open Frame
5 W
6.5 W
8 W
8 W
10 W
10 W
15 W
15 W
15 W
18 W
18 W
S Package (SOT-23-6)
1
6
FB
8
FB
2
5
7
GND
GND
3
4
6
ED
GND
5
ED
8
FB
7
GND
6
GND
5
ED
PI-7673-061516
1
2
CS
VCC
BD
October 2017

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Summary of Contents for Power integrations LinkSwitch-4 LNK4*15D Series

  • Page 1 Application Note AN-69 LinkSwitch-4 Family Design Guide and Considerations Introduction Output Power Table The LinkSwitch™-4 family of ICs dramatically simplifies low power 85 - 265 VAC CV/CC charger/adapter design by eliminating an optocoupler and Product Adapter secondary control circuitry. The LinkSwitch-4 family adaptive BJT drive Features Open Frame technology uses combined base and emitter switching to boost switching...

  • Page 2: Basic Circuit Topology

    Application Note AN-69 Scope converts the positive ramping primary current into a negative • ramping voltage, which is monitored by the PRIMARY CURRENT This application note is intended for engineers designing an isolated SENSE (CS) pin. It allows cycle-by-cycle peak primary current and AC-DC flyback power supply using the LinkSwitch-4 family of devices.

  • Page 3: Quick Start

    AN-69 Application Note Quick Start VCRMV-VMIN [E56-E57] is less than 15 V, but the higher VCRMV the better. The spreadsheet will produce a reasonable solution if To start immediately, use the following information to quickly design VOR is left at the default 100 V. the transformer and select the components for a first prototype.
  • Page 4 Application Note AN-69 If no-load to partial or full load transient step is required as in USB Component values for the design are found in: chargers: , CIN [E13] Enter the load step value into I_LOADSTEP [B148] if it is different Selected device –...
  • Page 5 AN-69 Application Note Step-by-Step Design Procedure Specify Application Customer / Data Sheet Parameters Defined; Assumptions Bulk Capacitor Determines Minimum HT Election Voltage at Full Load IC and BJT Power Range, CDC Selection Core Type ; Size ; Material Transformer Core, Bobbin, Turns .
  • Page 6 Application Note AN-69 General Guidance for Using the PIXls Design Minimum Required Output Current, I Spreadsheet This is the nameplate current and is the current that must be supplied at the nameplate voltage, before the VI curve follows the Only the information described below needs to be entered into the decreasing voltage CC characteristic.

  • Page 7: Output Power Table

    AN-69 Application Note ENTER APPLICATION VARIABLES Design title VACMIN 90 Volts Minimum AC Input Voltage VACMAX 265 Volts Maximum AC Input Voltage 50 Hertz AC Mains Frequency 5.00 Volts Output Voltage at the end of the cable VO_PCB 5.30 Volts Output Voltage at PCB.
  • Page 8 Application Note AN-69 Step 3 – Core and Bobbin Selection Based on Output Core Size Output Power Capability Power and Enter A EF12.6 3.3 W These symbols represent core effective cross-sectional area A EE13 3.3 W core effective path length L (cm), core ungapped effective inductance (nH/Turn ), bobbin width B...
  • Page 9 AN-69 Application Note Step 4 – Select Reflected Voltage and Secondary Turns the number of secondary turns in [B50] while sweeping the VOR value [B49] offers further optimization possibilities. These are the main optimization inputs that effect efficiency and the minimum DC bulk capacitor voltage the converter will operate at, The default primary inductance tolerance is 10%, an alternative value under full load.
  • Page 10 Application Note AN-69 Step 5 – Transformer Core Parameters entered into [B98] and the wire diameter will be reduced accordingly. The lower the number of primary layers, the lower leakage induc- The default peak core flux is set to 3900 Gauss. If the users selected tance is likely to be.
  • Page 11 AN-69 Application Note Step 7 – Bias / Feedback Winding Design Parameters For applications that have challenging start-up conditions, CC load and/or high output capacitance, a higher value of target V may be The bias / feedback winding performs two functions, as its name entered into [B107], 9 V for example.
  • Page 12 Application Note AN-69 Step 8 – Secondary Winding Design Parameters recalculate the number of layers or filars. It does recalculate the bare conductor diameter in [E120] and is useful for investigating the effect Generally only one winding layer is used for the secondary, but for on secondary winding current density.
  • Page 13 AN-69 Application Note Step 9 – Voltage Stress Parameters VOLTAGE STRESS PARAMETERS SWITCH_DERATING 0.10 %/100 Desired derating factor for switch VCOLLECTOR 605 Volts Maximum Collector Voltage Estimate (Includes Effect of Leakage Inductance) PIVS 27 Volts Output Rectifier Maximum Peak Inverse Voltage PIVB 49 Volts Bias Rectifier Maximum Peak Inverse Voltage...

  • Page 14: Step 10 - Additional Parameters

    Application Note AN-69 Step 10 – Additional Parameters Bias Capacitor - CVCC Bias Capacitor 5.38 uF Bias capacitor is greater than 2uF! Transient response could be unpredictable. For improved and repeatable transient response keep capacitor value < 2 uF CBIAS Voltage ripple on VCC capacitor at zero-load (should be between 0.05 V and 100 mV DELTAV_BIAS...
  • Page 15 AN-69 Application Note Output Capacitor C Load Step and Undershoot The spreadsheet will calculate the maximum size of output capacitor In this section the zero load transient response is evaluated. It is into which the circuit can start up. This is mainly governed by the essential to have the zero load switching frequency in [E154] greater size of the bias capacitor [E138], which has to supply power to the than the minimum undershoot switching frequency given in [E150].
  • Page 16 Application Note AN-69 Feedback Resistors value to obtain an accurate output voltage. In fact the spreadsheet sets the minimum HT voltage at start-up that will allow the will tend to result in a slightly high output voltage as the high current controller to continue to run.
  • Page 17 AN-69 Application Note Step 12 – Results Check Now that all the variables have been entered, the results can be Component values for the design are found in: assessed. , CIN ............... [E13] Selected device ..............[E20] Check entered values and options are correct. Q1 BJT ...................
  • Page 18 Application Note AN-69 Step 13 - Further Component Selection Input Stage IN1-4 AC IN PI-5118-042308 PI-5107-012615 Figure 24. Input Stage. The recommended input stage is shown in Figure 24. It consists of a fusible element (R ), input rectification (D ), and line filter network IN1-4 and L...
  • Page 19 AN-69 Application Note Supplementary Base Drive Common LinkSwitch-4 Transformer Topologies Resistor R is used on SO-8 packaged devices to provide extra base A simple 3 winding transformer structure has been developed that is drive in higher power applications (7.5 W – 18 W) without increasing suitable for all LinkSwitch-4 designs up to 18 W.
  • Page 20 Application Note AN-69 Figure 26. 3 Winding Transformer Construction. 5 Winding Transformer bias and compensation wind senses are in the opposite direction. The 5 winding transformer is wound as the primary first, with the On average this tends to make the trifilar winding have no net collector node pin as the start so that it is screened by succeeding electrostatic voltage change, so it acts like a foil screen, though an primary layers from the secondary.
  • Page 21 AN-69 Application Note Step 14 – PCB Layout Guidelines GROUND pin must not generate volt drops in the GND tracking that interfere with voltage on the FEEDBACK pin due to the GND Good layout practice helps with: connection of R The impedance driving the FEEDBACK pin is quite high.
  • Page 22 Application Note AN-69 SSNUB SSNUB BIAS VCC1 VCC2 PI-8164d-110116 Figure 29. Chip GND, R Connections. SSNUB SSNUB BIAS VCC1 VCC2 PI-8164a-110116 Figure 30. Primary Current Loop. The primary current loop (highlighted in Figure 30) must be kept One capacitor can be used, but this requires that the IC is also •...
  • Page 23 AN-69 Application Note SSNUB SSNUB BIAS VCC1 VCC2 PI-8164b-110116 Figure 31. V and Bias Current Loops. SSNUB SSNUB BIAS VCC1 VCC2 PI-8164c-110116 Figure 32. Input Components and Tracks Susceptible to Noise from BJT Collector Node. lead loop down to the output capacitor +V track.
  • Page 24 Application Note AN-69 Y Capacitor SSNUB SSNUB BIAS VCC1 VCC2 PI-8164e-110116 Figure 33. Y Capacitor Connection. nents. Although the collector node should be kept physically small to reduce EMI, it is possible to use the connection to conduct heat away Y Capacitor from the BJT, to the transformer.
  • Page 25 AN-69 Application Note The PCB has to provide the lowest possible impedance to ground Before modifying the circuit or applying a soldering iron to add/ • through the spark gap. remove components, it is essential to discharge the bulk capacitors completely.
  • Page 26 Application Note AN-69 Care must be taken to ensure V does not rise above 16 V, else the 10ms/div chip may be damaged. Zoom Area The bias winding voltage is related to the output voltage by the secondary/bias turns ratio. Initially the output voltage is zero due to the zero charge on the output capacitance and it takes time for the output voltage to rise to a level where enough voltage is generated by the bias winding to power the chip.

  • Page 27: Linkswitch-4 Functional Description

    AN-69 Application Note LinkSwitch-4 Functional Description To improve no-load power, the following steps can be taken; 1. Start-up resistor can be increased. 30 MW is a value that is FEEDBACK Pin usually used to provide a fast sub 1 second start-up, but 40 MW The transformer voltage is monitored by dividing the bias (feedback) should just be OK across production spreads for a universal input winding voltage and feeding the signal into the FB node.
  • Page 28 Application Note AN-69 The controller measures the FB source current to determine the voltage across the primary, and applies two thresholds, I Tangent Optimal Too little FBHT(LO) slope FBHT(START) is the threshold at which the primary voltage might be too low FBHT(LO) to sustain normal operation, or it may indicate that the FEEDBACK pin is not connected to the feedback winding due to a fault.

  • Page 29: Current Sense Pin

    AN-69 Application Note The voltage control loop aims to maintain the sampled value at otherwise switching will cease, V will fall and a power cycle , about 1.98 V, see data sheet. sequence will occur. If V falls by 1.6 V, an extra switching pulse FB(REG) is issued as if V had fallen to V...

  • Page 30: Emitter Drive Pin

    Application Note AN-69 Constant Current Control by the CURRENT SENSE Pin Average Voltage The controller evaluates the average voltage across R . This is used to control the maximum output current of the circuit. A current BD current control loop aims to limit the average voltage to V .

  • Page 31: Supplementary Base Drive Pin

    AN-69 Application Note This scheme allows for a wide range of BJT HFE characteristics to be driven efficiently with minimum power loss. As the drive is essentially ‘common base’, the full RBSOA of the BJT can be used i.e. V rating CC(RUN) is dominant, not V...

  • Page 32: Easystart Feature

    Application Note AN-69 resulting decrease in primary resistive losses. This will have the The extra diode only needs to be low voltage, 20 V+, and must effect of moving the maximum load operating point to the left on support the peak primary current over the duty cycle at the lowest AC Figure 49, to around 70-75% of V .
  • Page 33 AN-69 Application Note FILT 2 × R BRIDGE EasyStart Diode PI-8180-110916 Figure 51. Schematic with Extra Diode for EasyStart Feature. Thermal Shut Down The LinkSwitch-4 has a thermal shut down feature. If the junction temperature of the IC exceeds T , about 140 ºC, the chip will shut down and cease switching.
  • Page 34 Application Note AN-69 The first step is to use the LinkSwitch-4 PIXls tool to design the Where: transformer and component values for a CV/CC equivalent to the = Nominal primary inductance in Henries. CV/CP circuit. The important consideration is to have the CV/CP for LinkSwitch-4 device in volts, nominally 0.36 V.
  • Page 35 AN-69 Application Note Notes Rev. B 10/17 www.power.com...
  • Page 36 The products and applications illustrated herein (including transformer construction and circuits external to the products) may be covered by one or more U.S. and foreign patents, or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations patents may be found at www.power.com.

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