Design considerations of 65W active clamp flyback adaptor with MasterGaN Mike Chen Industrial Power & Energy Competence Center AP Region, STMicroelectronics
Design considerations of 65W active clamp flyback adaptor with MasterGaN
Mike Chen
Industrial Power & Energy Competence Center
AP Region, STMicroelectronics
Agenda
1 Travel adapter developing
2 Drawback of flyback
3
4 MasterGaN introduction
5 MasterGaN used in 65W ACF
6 Gate drive signal
7 Noise prevent-PCB layout
8 dv/dt Adjustment
2
ACF Used in smart shargerproduct
Travel adapter development
3
Power Level Increasing 5W 65W 120W
Power Density Increasing 5W/in3 20W/in3 30W/in3
Switching frequency Increasing 60kHz 150kHz 350kHz
Drawbacks of flyback
4
Drawbacks of traditional Flyback
β’ High power loss and spike caused by leakage
inductance of the transformer
β’ High switching loss of the main MOSFET due to the
spikeπ α»ππβππ(πΆππ π = πππΰΆ±
0
π α»π·π(ππΉπΉ
πΆπππ(πππ α»πππ ππππ
πππβππΉπΉ =πΌπ2ππΉπ΄πΏπΏ
2
6πΆ α»πππ(πππππ
πππ = πΌπ(π ππα»2 π π·π(ππα»
ACF used in smart charger
5
β’ The leakage inductance energy is recycled with clamp circuit, while the Turn-OFF
voltage stress across the power switch is minimized
β’ The ZVS of the power switch is achieved and subsequently the switching losses are
minimized
β’ Decrease the stress of the secondary rectifier diode
Time (s)
0
200
400
Vds
Time (s)
-2
0
2
Ids
Time (s)
-2
0
2
I(Csn)
Time (s)
0
0.4
0.8
QG_LS QG_HS
2.051m 2.052m 2.053m 2.054m 2.055m 2.056m 2.057m
Time (s)
0
5
10
15
20
I(Dout)
( α» 1
πΌπΆπ
πΌπ·π
ππΆπ ππ·π
π π(π2α»π π(π α»
πΌπ·π
ACF used in smart charger
6
PROs
β’ The energy of the leakage inductance is
recycled
β’ ZVS is achieved and switching losses are
minimized β High efficiency and high switching
frequency achievable
β’ Soft-switching architecture
CONsβ’ Additional clamp power switch with dedicated
high-side driver
β’ Increases the complexity of the controller
β’ Much more difficult to design and optimize
compared with a standard flyback
GaN vs. Silicon based transistors
7
β’ Gallium Nitride (GaN) is a wide-bandgap (WBG)
material. HEMT (High Electron Mobility
Transistor) gallium nitride (GaN) transistors, or
simply GaN transistor, represents a major step
forward in power electronics, providing high
frequency operation, increased efficiency and
higher power density compared with silicon-based
transistors.
GaN Silicon Comments
Qg-Gate charge Lower Higher GaN with lower driver loss to achieve higher
frequency & efficiency
Coss-Output capacitance Lower Higher GaN with lower switching loss to achieve higher
frequency & efficiency
Qrr-Reverse recovery charge Lower Higher GaN suitable for higher frequency & efficiency
Vgs- gate voltage Difficult Easy GaN need better gate drive circuit and PCB
layout
Vsd-body diode conduction Higher Lower GaN need better control of deadtime
MasterGaN1
8GQFN 9x9
Featuresβ’ Power system-in-package integrating half-bridge gate
driver and high-voltage GaN transistors:
β BVDSS = 650 V
β RDS(ON) = 150 mΞ©
β IDS(MAX) = 10 A
β’ Reverse current capability
β’ Zero reverse recovery loss
β’ UVLO protection on low-side and high-side
β’ Internal bootstrap diode
β’ Interlocking function
β’ Dedicated pin for shutdown functionality
β’ Accurate internal timing match
β’ 3.3 V to 15 V compatible inputs with hysteresis and
pull-down
β’ Overtemperature protection
β’ Bill of material reduction
β’ Very compact and simplified layout
β’ Flexible, easy and fast design
High power density half-bridge 650V GaN with embedded driver
MasterGaN1 pinout
9
Key benefits
β’ Compact system solution and
simplified layout
β’ BOM reduction:SiP with offline driver
optimized for GaN
β’ Robust solution: driver and GaN
power transistors integration
β’ Package GQFN 9x9
β’ Flexible, easy and fast design
β’ Scalable p2p solution for power
range 30-500 W
10
Applications
Telecom/Server Power
Power Supply for 5G
Communication
Infrastructure
EV/HEV Charging Stations
Energy Storage Systems
(UPS)
Solar DC-AC Converters
PC Power, OLED TV
High-Density AC-DC
Adapters, Fast Charging,
USB-PD
MasterGaN1 applications and benefits
MasterGaN family roadmapQFN 9x9 mm2 pin-to-pin scalable
MasterGaN1
Symmetrical
150 + 150 mΞ©
From 45 up to 400 W
MasterGaN4
Symmetrical
225 + 225 mΞ©
MasterGaN5
Symmetrical
500 + 500 mΞ©
MasterGaN3
Asymmetrical
225 + 500 mΞ©
MasterGaN2
Asymmetrical
150 + 225 mΞ©
Mass production MP Dec 2020 DevelopmentDevelopment Development
Whole product family to be released by H1 2021
One driver, many standard transistors for HB configuration
65W ACF Application example - MasterGaN
65W ACF Application example typical connection
Suggested 6V typ
Suggested 10ohm
Shunt is very common: LS driving is guaranteed
until the voltage difference between PGND and
GND is within +/-2V
Hi performance Ceramic Cap to be as close
as possible between HV and Sense and
between HV and VS
RC network for OTP
extended time constant
(*)
(*)
(*) External 6.2V Zener is suggested to protect the
GaNs from transient high voltage stresses
(**) In case of very small Duty cycles, external,
Low RD, high speed Bootstrap Diode is
recommended .. In case of intense negative
voltage on OUT, even Linear regulator is possible
(**)
65W ACF application example efficiency
14
84.00%
86.00%
88.00%
90.00%
92.00%
94.00%
96.00%
0 10 20 30 40 50 60 70
Eff
icie
ncy [
%]
Pout (W)
230Vac Input
230VAC 5Vout
230VAC 9Vout
230VAC 12Vout
230VAC 15Vout
230VAC 20Vout
88.00%
89.00%
90.00%
91.00%
92.00%
93.00%
94.00%
0 10 20 30 40 50 60 70
Eff
icie
ncy [
%]
Pout(W)
115Vac Input
115VAC 5Vout
115VAC 9Vout
115VAC 12Vout
115VAC 15Vout
115VAC 20Vout
Efficiency performance at low Line and high Line
65W ACF application example typical waveform
15
230 Vacin 20V/3.25A
Gate drive logic inputs β truth table
Disabled input port
Normal Operation
Configurations
Interlocking
Normal Operation Interlock Input disabled
HIN
LIN
GH
GL
SD/OD
Logic inputs β Interlocking
HIN
LIN
GL
OUT
HIN and LIN high never occurs, normal condition HIN and LIN high in black square β Interlock
GL and GH are both lowβ’ When Interlock condition is applied to the input, the active driver
is shut down after T(OFF)
β’ When Interlock condition is removed from the input, the new
input configuration is applied on the output after T(OFF)
MASTERGAN has an interlocking feature to prevent contemporary activation
of high side and low side.
Noise prevent-PCB layout
18
β’ VCC Filter caps placed to close VCC-GND Pins
Noise prevention - PCB layout
19β’ Keep signals traces away from OUT trace
β’ Keep bulk voltageβtransformer-OUT-SENSE-GND loop as small as possible
dv/dt adjustment
β’ During the design of power converters, the adjustment of dV/dt of middle point of
OUT pin is important to:
β’ Reduce EMI
β’ To avoid undesired oscillations when parasitic elements cannot be further minimised
β’ Reduce secondary side stress
dv/dt adjustment
OUT pin dv/dt at turn on: GaN turn-on when resonance has sufficient
amplitude to obtain ZVS
dv/dt adjustment
OUT pin dv/dt at turn off: Turn off dV/dt can be reduced using proper
selection of MASTERGAN biasing components
dv/dt adjustmentadding cap on GaNβs gate
β’ Adding a capacitor between GL (GH) and PGND (OUTb), is
equivalent to increase GaNβs Gate Charge
β’ Maximum value must be found to avoid driverβs dynamical
overstress and considering the operating frequency Fsw
β’ CGx<80mW/(Pvcc^2*Fsw)-(330pF)
PROs CONs
Fine tuning of the obtained effect
High repeatability of the effect thanks to the accuracy of
the available discrete components
Effect is also on EMI associated with normal operation
Additional operating consumption to PVCC and Vbo,
especially at high frequency
Not suitable for very high frequency solutions
Cpvcc CGL
Cboot CGH
β’ A resistor in series with
PVCC or VBO decreases
the driving current.
β’ A very short drop is evident
on PVCC / VBO at driver
turn on.
Adding a resistor on PVCC
PROs CONs
Fine tuning of the obtained effect
High repeatability of the effect thanks to the accuracy of the
available discrete components
Effect is also on EMI associated with normal operation
PVCC / VBO drop can increase the propagation delay
Short-on time can result into worse Rdson because of the reduced
Ganβs gate overdrive voltage (i.e. PVCC-Vgsth)
Duration of VBO drop must be shorter than 2 Β΅s to prevent UVLO
activation
Cpvcc
Cboot Rbo
Rpvcc
RGONH
RGOFFH
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120 140 160 180 200 220
Slo
pe
(V
/ns)
RPVCC (or RVBO)
dV/dt turn on slope
Tj=0Β°C
Tj=25Β°C
Tj=100Β°C
Tj=125Β°C
RGONL
RGOFFL
β’ An RC network feedback can be added between
OUT node and GL in order to reduce the GL voltage
in case of intense negative dV/dt.
β’ Consider to use PCB, especially for thin PCBs,
instead of the added Ck
Example
β’ 0.8mm 4 layer PCB, 0.1mm inner core thickness,
Ξ΅r=4.4
β’ 10pF -> 30mm2: can fit below MasterGaN
dv/dt Adjustment - adding dv/dt killer
PROs CONs
Acts on high dV/dt only: the dV/dt value is then balanced over
entire operating conditions
High voltage component needed
Cpvcc
Ck
CbootCGH
Rdamp
β’ The value of the Capacitor (Ck) limits the dV/dt during hard switching
thanks to Miller effect
β’ During turn on the rate is limited to ~ππππΆπΆβπππ»
π πππΊπΆπ=
ππππΆπΆβ .7
50βπΆπ
β’ During turn off, it is limited to ~πππ»
π ππΉπΉπΊπΆπ=
0.85
πΆπ
β’ A resistor in series is required to avoid oscillations due to stray inductance
β’ π π·π΄ππ β«πΏπ π‘πππ¦
πΆπ
β’ Capacitor required is typically 5pF to 10pF (600V rated)
β’ E.g.: Using PVCC = 6V and max dV/dt = 10V/ns β Ck = 8.6pF
Adding dV/dt limiter β design tips
dv/dt adjustment - adding dv/dt killer
27
OriginaldV/dt equal to 37V/ns
With dV/dt limiter cap 10pF / 200Ξ©
dV/dt limited to 6V/ns
β’ Startup waveforms at 230VAC compared
β’ dV/dt changed from original 37v/ns to 6v/ns
28
dv/dt adjustment - adding dv/dt killer
Turn on: 1.85V/nS Turn off: 6.6V/nS
Example of the 65W board: Rpvcc=15Ξ© Cg=470pF R43=200Ξ© C57=10pF
220V/50Hz input 20V/3.25A output
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