AppNote Number
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
RONG Rui
ATV SYS
About this document
Scope and purpose
The power stage was developed to support customers during their first steps in designing 48V inverter for Beltdriven Starter Generator (BSG) application. The document provides a detailed description of the main
components and their functionality. This information is intended to enable the customers to re-use and modify
the original design and qualify their own design for the production, according to their own specific
requirements.
Application Note
www.infineon.com
Please read the Important Notice and Warnings at the end of this document
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Introduction
Table of Contents
About this document ....................................................................................................................... 1
Table of Contents ........................................................................................................................... 2
1
Introduction.................................................................................................................. 3
2
2.1
2.2
2.3
2.4
Quick Start Guide........................................................................................................... 5
Block Diagram ......................................................................................................................................... 5
System with heatsink .............................................................................................................................. 5
Connector ................................................................................................................................................ 6
Power Terminals ..................................................................................................................................... 8
3
3.1
3.2
3.2.1
3.2.2
3.2.3
Design Features ............................................................................................................. 9
Inverter specification .............................................................................................................................. 9
Key components...................................................................................................................................... 9
Bus bar and capacitors ...................................................................................................................... 9
Power Board ..................................................................................................................................... 10
TOLL & TOLG MOSFET ...................................................................................................................... 11
4
4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3
4.4
4.5
4.6
4.7
4.8
Function description and design implementation ............................................................. 13
Power loss Calculation .......................................................................................................................... 13
Thermal Estimation ............................................................................................................................... 15
Cooling structure.............................................................................................................................. 15
Temperature rise estimation ........................................................................................................... 15
Thermal simulation .......................................................................................................................... 15
Copper based IMS board thermal consideration ............................................................................ 17
TOLG MOSFET for Al based IMS board............................................................................................. 18
Driver IC and circuit analysis ................................................................................................................. 19
Schematic .............................................................................................................................................. 19
Mechanical boundary ............................................................................................................................ 23
Stray inductance consideration ........................................................................................................... 23
Components Arrangement and Layout ................................................................................................ 25
Bill of materials...................................................................................................................................... 28
5
5.1
5.2
5.3
5.3.1
5.3.2
5.3.2.1
5.3.2.2
5.3.2.3
5.4
5.5
Measurement results..................................................................................................... 29
X-ray check ............................................................................................................................................ 29
Switching behavior................................................................................................................................ 30
Thermal distribution ............................................................................................................................. 31
Static state thermal distribution ..................................................................................................... 31
Dynamic thermal distribution ......................................................................................................... 34
Lab Test with 400Arms output of inductor load ........................................................................ 34
Bench test with 40Nm load ......................................................................................................... 35
Bench Test with 50Nm load ........................................................................................................ 38
Torque Speed characteristics ............................................................................................................... 41
Voltage ripple ........................................................................................................................................ 42
6
Summary ..................................................................................................................... 46
7
Reference .................................................................................................................... 47
Application Note
2
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Introduction
1
Introduction
The power stage shown in Figure 1 was developed to support customers during their first steps in designing 48V
inverter for BSG applications. A logic board with driver circuit is necessary for evaluation. The following
chapters provide a detailed description of the main components and their functionality. This information is
intended to enable the customers to re-use and modify the original design and qualify their own design for the
production, according to their own specific requirements.
The boards provided by Infineon Technologies are subjected to functional testing only.
The current implementation of the design is for reference only! It does not cover in general all application
specific requirements. For specific recommendations on how to implement designs with TOLL MOSFET, please
contact your local Infineon sales partner. More information is available on www.infineon.com.
Due to their purpose the system is not subjected to the same procedures regarding Returned Material Analysis
(RMA), Process Change Notification (PCN) and Product Withdraw (PWD) as regular products.
See Legal Disclaimer and Warnings for further restrictions on Infineon Technologies’ warranty and liability.
Figure 1
Overview of the power stage
Application Note
3
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Introduction
Belt-driven Starter Generator (BSG) is used as a motor in the Micro-Hybrid vehicle to enhance the output torque
of the engine. Inverter of BSG need compactly mounted on the bottom of motor. The power supply is DC 48V.
The peak power is 12kW. The power stage including paralleled MOSFET should be assigned on a round shape to
fit the shape of the motor. The output current will be up to 400Arms. More than 550W power loss would be
generated. The challenge is to get 3 key performances in 150mm diameter round space. The performances are:
well-balanced current in the paralleled MOSFET, low VDS spike at switching off, low Rth of heatsink system.
Using customized MOSFET module is the state of art. The outline of the module is fixed by specific motor. It’s
not easy to reuse in other project. So that different customer should customize different module. Even the
same customer should customize several modules for different vehicle platform.
This reference design is a solution of discrete MOSFET with IMS board. It is very easy to reuse and modify for
customer to adapt their system. The scalability and feasibility are the strength of this reference design.
Customer can change the RDSon with same package to get different power capability. And reduce the number of
paralleling MOSFET is another good choice for tuning the size and the power capability. The current are well
balanced so that the temperature deference could be down to 2°C. The VDS spike of switching off 570A current is
only 19V at 48V DC bus. Rth of junction to coolant could be around 2 K/W.
Note: A logic board with driver circuit is necessary for evaluation.
Application Note
4
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Quick Start Guide
2
Quick Start Guide
The power stage should be used with heatsink and be connected with power cable and signal cable. Chapter
2.1 shows the block diagram of BSG inverter. Chapter 2.2 shows the heatsink. Chapter 2.3 shows the signal
connector. Chapter 2.4 shows the power terminals.
2.1
Block Diagram
Figure 2 shows the block diagram of the inverter. The parts in red rectangle are the power stage including
MOSFETs and DC bus capacitor bank. Four MOSFET paralleled as a switch.
Figure 2
Block diagram of the inverter
2.2
System with heatsink
The power stage can be mounted on the rear of the target motor. For lab test, it should be mounted on a water
or air cooling heatsink with thermal grease. Less than 5A can be handled in 5 minutes without heatsink.
Thermal grease should be used between heatsink and the IMS board. There should be a groove on the heatsink
for the capacitors terminal on the bottom of bus bar as show in Figure 3. The depth of the groove is 3mm. The
Figure 4 shows the power stage with water cooling for lab test.
Figure 3
Assembly structure with the groove on the Heat sink
Application Note
5
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Quick Start Guide
Figure 4
Power stage with water cooling heatsink for lab test
2.3
Connector
There is only one connector for all the gate driving signals. The part number of the connector is TFM110-22-S-DP from Samtec. User needs Samtec SFSD-10-28-G as corresponding connector.
Table 1 and Figure 5 show the Pin Assignment of the connector.
Table 1
Connector description
Pin Number
Name
1
T1
Terminal 1 of NTC
2
T2
Terminal 2 of NTC
3
P_GND
Ground for GL3
4
P_GND
Ground for GL1
5
GL3
Low side gate 3, voltage level 5~15V
6
GL1
Low side gate 1, voltage level 5~15V
7
SH3
High side source 3
8
SH1
High side source 1
9
GH3
High side gate 3, voltage level 5~15V
10
GH1
High side gate 1, voltage level 5~15V
11
NC
Not connected
12
NC
Not connected
13
P_GND
Ground
14
P_GND
Ground for GL2
Application Note
Description
6
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Quick Start Guide
Pin Number
Name
15
GH2
High side gate 2, voltage level 5~15V
16
GL2
Low side gate 2, voltage level 5~15V
17
SH2
High side source 2
18
P_GND
19
NC
Not connected
20
NC
Not connected
Figure 5
Description
Ground
Pin Assignment of connector
Please check layout of connector in Figure 6 to make sure the correct connection.
Application Note
7
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Quick Start Guide
Figure 6
Layout of the Connector
2.4
Power Terminals
As shown in Figure 7, there are 5 power terminals. The DC+ and DC- connect to 48V power supply. The M8 screw
U,V,W connect to the 3 phase motor.
Figure 7
Power Terminals
Application Note
8
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Design Features
3
Design Features
3.1
Inverter specification
The inverter specification describes the working condition of the power stage as shown in Table 2. This
specification is not directly limited by the power stage. The power stage is designed for such inverter and motor
system. The target motor is Permanent Magnet Synchronous Motor (PMSM). The most critical specification for
power stage is the peak phase current.
Table 2
Name
Min.
Typ.
Max.
Unit
Description
VDC_motoring
36
48
52
V
Motoring mode DC bus voltage
VDC_generating
36
48
54
V
Generating mode DC bus voltage
Output Power_motoring
3.8
kW
Motoring mode output power at 48V
Output Power_generating
2.6
kW
Generating mode output power at 48V
Peak Power_motoring
11.3
kW
Motoring mode peak power at 48V 10 sec
Peak Power_generating
12.8
kW
Generating mode peak power at 48V 10 sec
Iout_con
160
Arms
Motoring mode continuous phase current
Iout_max1
400
Arms
Motoring mode peak phase current 10sec
Iout_max1
500
Arms
Motoring mode peak phase current 0.5sec
Igen_con
160
Arms
Generating mode continuous phase current
Igen_max
400
Arms
Generating mode peak phase current 10sec
10
kHz
Switching frequency
Fsw
5
Motoring frequency
1000
Hz
Generating frequency
1000
Hz
95
°C
Coolant Temperature
65
3.2
Key components
3.2.1
Bus bar and capacitors
Ten aluminum capacitors soldered on the bus bar as shown in Figure 8. The part number of the capacitor is
EGPD101ELL621MM30H from Chemi-Con. Table 3 shows the key features of the capacitor. Additionally if the
max BEMF of the motor is lower than 80V, the 80V 820uF capacitor is a better choice. The part number is
EGVD800ELL821MM30H. It has higher vibration resistance by GPD series (acceleration 392m/s2, 40G).
Table 3
Key feature of ALUMINUM ELECTROLYTIC CAPACITORS
Rated ripple
current
Temperature
Range
DC Voltage
Capacitance
EGPD101ELL621MM30H
3.92A
-40°C to 135°C
100V
620uF
EGVD800ELL821MM30H
3.93A
-40°C to 135°C
80V
820uF
Application Note
9
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Design Features
The DC+_A and DC-_A terminals connect to the power supply. The DC+_B and DC-_B connect to the power
board with M6 screw as shown in Figure 8.
Figure 8
Bus bar and capacitors overview
3.2.2
Power Board
There are four M6 screws and three M8 screws on the power board as shown in Figure 9. M6 screws in left
connect to the capacitor bank. M8 screws connect to the phase of the motor.
The Insulated Metal Substrate (IMS) material is used. The detail of IMS board is shown in Table 4.
The thickness of the copper is 3oz (0.105mm), it helps to handle 400A~500Arms while the width of copper plane
is around 10mm.
The thickness of the Aluminum substrate is 2mm which handle the dynamic thermal behavior, for example
start the engine in 300ms with 500Arms output current.
Figure 9
Power board overview
Application Note
10
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Design Features
Table 4
IMS board material
Items
Features
Board type
Thermal Clad HT04503
Copper thickness
3oz (105um)
Aluminum carrier thickness
2mm
Insulator layer thickness
76um
3.2.3
TOLL & TOLG MOSFET
The TO-Leadless (TOLL) is a molded package optimized for high power high reliability applications. Its small
mechanical dimensions allow really compact designs and the high current capability combined with the low
Thermal Resistance (RthJC), resulting in lower chip temperatures enables the designer to go for higher power
density and higher reliability.
Furthermore, Infineon investigated a derivate of the TOLL to improve thermal cycling on board (TCoB)
performance on Al-core IMS board. It is called TO-Leaded with Gullwing geometry (TOLG). The footprint of
TOLG could be compatible with TOLL.
Compared to the commonly used D2PAK or D2PAK 7Pin the TOLL & TOLG has a smaller footprint. The size of
TOLL and TOLG are 11.7mm * 9.9mm * 2.3mm and 11.7mm * 9.75mm * 2.3mm comparing to the 15.0mm *
10.0mm * 4.4mm of the D2PAK (7Pin) as shown in Figure 10. This leads to a 30% smaller footprint and a 60%
smaller space.
Figure 10
Space reduction of TOLL & TOLG compared to D2PAK 7Pin
Figure 11 shows the calculated typical Zth-JC of junction to case of D2PAK, TOLL and TOLG package. The 0.1K/W
reduction of thermal resistance makes no sense to a normal board level thermal system, as the total RthJA from
junction to ambient could be about 40K/W. But it’s worth to use the reduction in a well cooling system. For
example, the IMS board with water cooling system has very low total RthCA from junction to coolant like 2K/W.
Application Note
11
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Design Features
Figure 11
ZthJC (calculated) of D2PAK 7Pin, TOLL and TOLG
AEC-Q101 qualified TOLL & TOLG MOSFETs are available for automotive application as shown in Table 5.
Table 5
Key feature of TOLL & TOLG MOSFET
Part NO. of TOLL
Part NO. of TOLG
VDS
RDSon,max
ID,nom
Operating
Temp.
IAUT165N08S5N029
IAUS165N08S5N029
80V
2.9mohm
165A
-55°C~175°C
80V
2.3mohm
200A
-55°C~175°C
80V
1.9mohm
240A
-55°C~175°C
80V
1.4mohm
300A
-55°C~175°C
80V
1.2mohm
300A
-55°C~175°C
IAUT165N10S5N035
100V
3.5mohm
165A
-55°C~175°C
IAUT300N10S5N015
100V
1.5mohm
300A
-55°C~175°C
IAUT200N08S5N023
IAUT240N08S5N019
IAUS240N08S5N019
IAUT300N08S5N014
IAUT300N08S5N012
Application Note
IAUS300N08S5N012
12
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
4
Function description and design implementation
4.1
Power loss Calculation
The power loss calculation in Ref. [2] is used for thermal estimation. There are four MOSFETs in paralleled as a
switch. Assuming the current of MOSFET is well balanced. The formulas are using for the power loss calculation
of the MOSFET.
The total power losses are divided as MOSFET power loss (PM) and Diode power loss (PD). PM is divided as
conduction loss (PCM) and switching loss (PSWM). PD is divided as conduction loss (PCD) and switching loss (PSWD) as
well.
2
PM = PCM + PswM = R DSon ∙ IDrms
+ (EonM + EoffM ) ∙ fsw
2
PD = PCD + PswD = uD0 ∙ IFav + R D ∙ IFrms
+ EonD ∙ fsw
The conduction loss could be calculated using an MOSFET-approximation with the drain-source on-state
resistance (RDSon). The conduction losses of the body diode can be estimated using a diode approximation with
a series connection of DC voltage source (uD0) representing diode on-state zero-current voltage and a diode onstate resistance (RD).
1
8
2
PCM = R DSon ∙ IDrms
= R DSon ∙ Io2 ∙ ( +
ma ∙cos ϕ
)
3π
1 ma ∙ cos ϕ
1 ma ∙ cos ϕ
2
PCD = uD0 ∙ IFav + R D ∙ IFrms
= uD0 ∙ Io ∙ ( −
) + R D ∙ Io2 ∙ ( −
)
2π
8
8
3π
The switching power loss could be calculated from the switching energy and switching frequency (fsw). The
switching energy could be calculated from parameters in the Datasheet refer to Ref. [1].
EonM = EonMi + EonMrr = UDD ∙ IDoff ∙
EoffM = UDD ∙ IDoff ∙
EonD ≈ EonDrr =
Application Note
tri + tfu
+ Q rr ∙ UDD
2
tru + tfi
2
1
∙Q ∙U
4 rr DD
13
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
The input values are shown in Table 6. The value of R1 and R2 are explained in Chapter 4.3.
Table 6
Input parameters
Parameters
fsw
Iload
VDS
m
phi
V_plateau
Vdr
Vth
Rhi
Rg
Rg_internal
Ciss
Crss
rdson
rfdiode
Vfo
Qrr
Cgd1
Cgd2
tri0
tfi0
R1
R2
Vf_D1
Value
10000
40, 100, 125
48
0.85
0.555
4.3
12
2
0.03
0
1.9
11200
69
0.0033
0.003535
0.4
232
70
1100
58
18
5.1
15
0.3
Unit
hz
Arms
V
rad
V
V
V
ohm
ohm
ohm
pF
pF
ohm
ohm
V
nC
pF
pF
ns
ns
ohm
ohm
V
The results of power loss are shown in Table 7. 5.38W was used for steady state thermal simulation. The power
loss of 23.3W in 10 seconds and 34.3W in 0.5 second could be used in dynamic thermal simulation.
Table 7
Power loss calculation result
Phase Current
Current of each MOSFET
Power loss of each MOSFET with body diode
160Arms
40Arms
5.38W
400Arms
100Arms
23.3W
500Arms
125Arms
34.3W
Application Note
14
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
4.2
Thermal Estimation
4.2.1
Cooling structure
Figure 12 shows the cooling structure of power stage. Please refer Figure 12 as an example. The MOSFETs were
soldered on the IMS board. The IMS board has copper layer, dielectric layer and aluminum layer. The IMS board
was mounted on a water cooling heatsink with thermal grease.
Figure 12
Cooling structure of power stage
4.2.2
Temperature rise estimation
During design phase the temperature rise of steady state could be estimated from power loss multiplying
thermal resistance.
∆𝑇𝑗 = 𝑃 × 𝑅𝑡ℎ _𝐽𝐴
The thermal resistance junction to case is 0.4K/W. The thermal resistance of IMS board is 0.45K/W. The thermal
resistance of thermal grease could be estimated as 1K/W. The total thermal resistance is estimated as 2K/W.
The temperature rise of steady state could be estimated as
∆Tj = 5.38W * 2K/W = 10.76°C
4.2.3
Thermal simulation
Figure 13 shows the thermal simulation with ideal environment.
Ambient temperature is 45°C. The thickness of thermal grease is TP-1500 with 0.25mm thickness and 10psi
pressure. Power loss of MOSFET is 5.38W. MOSFETs are placed on the IMS board with an ideal heatsink and
cooling by water at 65°C. The simulation result of temperature plane in top layer give draft understanding of
thermal distribution and thermal coupling of the design.
Application Note
15
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 13
Thermal Estimation of MOSFET on IMS board
Figure 14
Temperature difference between junction and case
Chapter 4.1 shows the power loss of MOSFET in three conditions. It is acceptable that the temperature rise of
junction at 160Arms would be around 10 degrees from simulation and estimation.
Furthermore it is shown in Figure 14 that the temperature difference between junction and case of MOSFET was
about 2.6°C. The main part of power loss sink through bottom side to the water cooling heatsink. The case
temperature could be easily measured by a thermal camera. The junction temperature could be calculated
with the simulation result.
Application Note
16
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
The temperature rise of junction at 400Arms and 500Arms is a dynamic value in this application. The 500Arms
phase current is additional requirement as cold start mode in BSG. These data are measured on test bench and
verified in Chapter 5.3. Further simulation shows that the dynamic temperature difference between junction
and case of MOSFET could be 20°C. It is necessary to consider the margin at dynamic state.
4.2.4
Copper based IMS board thermal consideration
Due to different thermal expansion coefficients (CTE) between FR4 and Al, Al-based IMS substrate (CTE~25.5
ppm/K) is much stiffer than usual FR4 boards (CTE~14-16 ppm/K). Therefore, there is much more strain on the
soldering material between pins and IMS Substrate. More detail was described in Ref. [3].
On Al-IMS, as compared to the FR4, lifetime of solder material is significantly lower for TOLL packages. This
phenomenon is independent on the MOSFET or IMS provider. Packages with gullwing-type leads still achieve
high lifetime.
Another possible workaround is usage of Cu-based IMS (CTE~17 ppm/K) which has same results as FR4. Copper
has better performance in thermal perspective. Table 8 shows the comparison between the copper and
aluminum.
Table 8
Comparison between copper and aluminum
Copper
Aluminum
Thermal conductivity
401 W/(mK)
237 W/(mK)
Specific heat capacity
0.385 J/(g °C)
0.902 J/(g °C)
Density
8.96 g/cm^3
2.70 g/cm^3
Heat capacity in same volume
3.45 J / (cm^3 °C)
2.44 J / (cm^3 °C)
The copper has 70% better thermal conductivity than aluminum. That means the thermal resistance of the
metal layer will be 70% better when copper was used. Notice that the Rth of the metal layer is not the main part
of the Rth between junction and coolant.
The steady state simulation result with copper based IMS board was shown in Figure 15. It shows that the
temperature rise will be 5% lower than aluminum based IMS in Figure 14.
Figure 15
Temperature of junction and case on copper based IMS board
The copper has 40% more thermal storage capacity than aluminum. If the 2mm aluminum layer is replaced by
1.6mm thickness copper, the thermal storage capacity of copper will be 13% better than aluminum. This helps
the dynamic thermal performance of the MOSFET. Furthermore the steady state 1.6mm Cu based thermal
performance was simulated. The three scenarios are compared in Figure 16.
Application Note
17
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Temperature rise of Junction
Cu based VS Al based IMS
14
12
10
8
6
4
2
0
2mm Al
Figure 16
2mm Cu
1.6mm Cu
Comparison of junction temperature rise
The solution with 1.6mm copper layer will be slightly better than 2mm aluminum. The reliability of thermal
shock is the main motivation to do this analysis.
4.2.5
TOLG MOSFET for Al based IMS board
The TOLG package MOSFET is recommended for all users who intend to use Al-based IMS board. The
performance of new package TOLG is much better than TOLL on the AL based IMS board under same condition,
although the TOLL fulfills the standard TCoB requirements as shown in Figure 17 . The reason for better
performance is the flexibility of the gullwing leads.
Figure 17
Comparison of TOLL and TOLG under TCoB test
Application Note
18
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
4.3
Driver IC and circuit analysis
Driver IC consideration: The MOSFET has very low resistance but the gate charge is high. Four MOSFET in
parallel has maximum 828nC gate charge totally. It’s better to design a 10mA charge pump circuit for high side
switch. The bootstrap circuit could be not enough for high side power supply.
If the switching on and switching off circuit needs to be optimized separately on trade off on EMI and thermal
perspective, the circuit in Figure 18 is proposed. The R1 and R2 are mentioned in the Table 6 for power loss
calculation. R1 and Schottky diode D1 are on the driver board and R2 are on the IMS board as separate gate
resistors. D1 help to switch off faster as clamping diode.
The comparison between using and not using the D1 and R1 is shown in Table 9. It shows that the peak current
of gate is reduced and the switching off voltage threshold is lower with the same power loss.
Table 9
Without R1 and D1
With R1 and D1
Ig_on max
1.82A
0.82A
Ig_off max
1.01A
0.95A
Voff threshold
3.92V
3.85V
Power loss per MOS @500A
57.9W
57.5W
Figure 18
Driver circuit of paralleling MOSFET
4.4
Schematic
The schematic of the IMS board are shown in Figure 19 to Figure 22.
Each MOSFET has separated gate resistor (e.g. R1~R4). Four MOSFET in parallel has a common pull down
resister (e.g. R5) and common Zener (e.g. D1). The jumpers (e.g. X2) make the layout to be possible on a single
copper layer. The 100nF capacitors parallel with the MOSFET as a snubber circuit (e.g. C1, C2). R49 is a NTC
resister for temperature measurement. C3, C6, C9, C21, C22, C23 are 4.7uF 100V MLCC which close to each half
bridge.
Application Note
19
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 19
Schematic U phase
Application Note
20
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 20
Schematic V phase
Application Note
21
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 21
Schematic W phase
Application Note
22
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 22
Schematic Connector, NTC resistor and snubber
4.5
Mechanical boundary
The power stage should be mounted at the end of the motor, so that there is mechanical boundary of the
design. The diameter of the motor is 170mm. There should be place for current sensor and power terminal
connecting. The diameter of power stage is defined as 145mm and the height is less than 40mm.
Furthermore, the space above the power stage would be occupied by control board with microcontroller and
driver circuit. The components placement should take account of the control board.
4.6
Stray inductance consideration
When the MOSFET switch off with high current, the VDS spike should be analyzed to avoid avalanche of MOSFET.
Application Note
23
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
The switching-off voltage spike is determined by the stray inductance of the system and the change rate of
turn-off current, which is calculated according to the following formula:
Vs=Ls * di/dt
Ls indicates stray inductance of the system, di/dt indicates the change rate of current. Figure 23 shows the
overshoot of VDS waveform.
Figure 23
VDS overshoot cause by stray inductance and switching off speed
The laminated busbar was used to minimize the stray inductance of the busbar.
The stray inductance of the PCB layout should be calculated as a microstrip line as shown in Figure 24.
Figure 24
Microstrip line structure
The inductance of microstrip line could be calculated as following equation:
2𝐿
𝐿𝑚𝑖𝑐𝑟𝑜𝑠𝑡𝑟𝑖𝑝 = 2 × 𝐿 × [ln (𝑊+𝐻) + 0.5 + 0.2235 ×
(𝑊+𝐻)
𝐿
]
Lmicrostrip means inductance of the microstrip line in nH
W means width of the microstrip line in cm
Application Note
24
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
L means length of the microstrip line in cm
H means distance between the microstrip line and ground in cm
If the width is 1cm and the length is 10cm, the inductance is about 70nH. The inductance with different length
and width are shown in Figure 25 and Figure 26. The length of the trace should be as short as possible, but the
width is not critical especially when the width is wider than 10mm.
Inductance VS Length
80
Inductance (nH)
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
18
20
Length (cm)
Figure 25
Microstrip line inductance VS Length. The width is fixed at 10mm.
Inductance VS Width
120
Inductance (nH)
100
80
60
40
20
0
2
4
6
8
10
12
14
16
Width (mm)
Figure 26
Microstrip line inductance VS Width. The length is fixed at 5cm.
4.7
Components Arrangement and Layout
Figure 27 shows the components arrangement of the IMS board.
Each MOSFET has its own gate resistor. The gate resistor is left side of the MOSFET and close to gate pin. The
distance between each paralleled MOSFET is about 2mm which help to decouple the thermal effect. The
MOSFET are around the phase output terminal so that the current and the thermal are well distributed.
Application Note
25
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
The connector in the middle connects to six gate and source signals with jumpers.
Figure 27
Components arrangement
Figure 28 shows the layout of copper layer on the IMS board. Copper plane of DC+ is placed in the form of circle;
it connects the bus bar at the end, and connects drain of 12 high-side MOSFETs. The copper plane of each
phase is placed in the middle of the circle as shown in Figure 28. The copper plane of DC- is placed in the center
of the circle. Notice that the NTC resister for temperature measurement cannot measure the package
temperature or junction temperature as it is far away from the MOSFET. It shows the board temperature which
is related to the coolant temperature.
Application Note
26
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
Figure 28
The layout of the copper layer
Application Note
27
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Function description and design implementation
4.8
Bill of materials
Table 10 shows the BOM of the power board excluding the dc-link capacitors, bus bar, screws and nuts.
Table 10
Bill of materials
#
Qty.
Designator
Manufacturer
Part Number
Description
1
7
C1, C2, C4, C5, C7, C8, C10
AVX
12061C104K4Z2A
2
6
C3, C6, C9, C21, C22, C23
TDK
C5750X7R2A475K230KA
3
6
Vishay
BZT55B15
4
24
Infineon
Technologies
IAUS240N08S5N019
1.9mohm 80V Nchannel MOSFET
5
24
Yageo
/Phycomp
AC0805FR-0715RL
15/150V/1%
6
6
D1, D2, D3, D4, D5, D6
Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9,
Q10, Q11, Q12, Q13, Q14, Q15, Q16,
Q17, Q18, Q19, Q20, Q21, Q22, Q23,
Q24
R1, R2, R3, R4, R13, R14, R15, R16,
R17, R18, R19, R20, R29, R30, R31,
R32, R33, R34, R35, R36, R45, R46,
R47, R48
R5, R9, R21, R25, R37, R41
100n/100V/X7R
4.7uF/100V/10%/X
7R/125°C
Zener Diode/15V
Vishay
CRCW080510K0FKEA
7
1
R49
Vishay
NTCS0603E3103FMT
8
1
X1
TFM-110-22-S-D-P
9
9
X2, X3, X4, X5, X6, X7, X8, X9, X10
Samtec
Keystone
Electronics
10k/150V/1%
NTC resistor
10k/1%/0603
SMT connector
Silver Plate SMD
Jumper
Application Note
28
5104TR
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
5
Measurement results
Table 11 shows the summary of tests.
Table 11
Test item
Result
X-ray check
Air bubbles under MOSFET
Switching behavior
VDS 65V at VDC 46V
Thermal distribution
Thermal resistance is about 2K/W. The junction temperature is 150°C at
the most critical transient working condition.
Torque Speed characteristics
Meet the design target at motoring mode and generating mode
Voltage ripple
Meet VDA320
5.1
X-ray check
Equipment:
X-ray
Description:
Check if there are bubbles under 24pcs MOSFET
Result & Analysis:
The air bubbles area is 40~50% as shown in Figure 29 to Figure 30.
Calculation was done as follow to estimate the influence:
Thickness of solder:
0.05mm
Thermal conductivity of solder:
60 W/mK
Area of pad:
50mm2
Rth of solder:
0.05*1E-3 / 60 / 50*1E-6 = 0.017 K/W
If contact area decrease to 50%, Rth would be 0.035K/W.
It cause 0.4°C temperature rise when power is 23W corresponding 400Arms output. It cannot be accepted from
the quality perspective, but it could be used for thermal evaluation and lab test.
Application Note
29
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 29
X-ray picture 1
Figure 30
X-ray picture 2
5.2
Switching behavior
Switching behavior test shows the over voltage of the VDS at switching off. Figure 31 is the waveform of 570A
switching off. C1 is the VGS signal. C2 is the VDS of the four paralleled MOSFET. C3 and C4 is the current on the
two DC- screws measuring by ultra mini rogowski coil referring Figure 8 and Figure 9. C3+C4 are total ID current.
The VDS peak value is 65V when the VDC is 46V. The voltage spike is 17V.
Application Note
30
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 31
VDS waveform of 570A switching off
C1 (yellow): VDC, C2 (purple): VDS, C3 (blue): ID1, C4 (green): ID2, Math (red): ID1+ID2
5.3
Thermal distribution
Thermal distribution test shows the thermal performance of the MOSFET and DC-link capacitors.
5.3.1
Static state thermal distribution
The static state thermal test is critical for the DC-link capacitors.
Test condition is shown as follow:
VDC:
48V
Load type:
Inductor load
Twater:
18.8°C
Electrical frequency: 15Hz
Liquid flow:
13L/min
Duration:
15min
Iphase:
160A
Figure 32 shows the three phase current waveform at 160Arms.
Application Note
31
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 32
160Arms three phase current wave form
Figure 33 shows VGS waveform at 160Arms. The green line is high side VGS of W phase. The orange line is low side
VGS of low side.
Application Note
32
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 33
VGS at 160Arms output.
Figure 34 shows the thermal distribution. The MOSFETs were well cooling by the liquid cooling heatsink and
reach static state in several minutes. It shows that there is 10°C temperature rise on MOSFET. RthCA of case to
coolant was calculated as about 2K/W. The junction temperature would be several degrees higher than case at
continuous working condition. The temperature of DC-Link capacitors was up to 40°C. The DC-link capacitors
were cooling by still air. It shows that the DC-link capacitors need external heat sink to handle the thermal at
continuous condition.
Figure 34
Steady state thermal distribution of the power stage @160Arms
Application Note
33
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
5.3.2
Dynamic thermal distribution
The dynamic thermal test is critical for the MOSFETs. Three dynamic thermal tests were done.
The first one is lab test with 400Arms output of inductor load. The second one is bench test with 40Nm load.
The third one is bench test with 50Nm load.
5.3.2.1
Lab Test with 400Arms output of inductor load
Equipment:
Inductor load
Driver board
SVPWM generator
Cooling System
48V Power Supply
Thermal Camera
Description:
48V 400Arms with inductor load
Check VDS and VGS PWM signal
Thermal of Tc
Test condition：
VDC: 48V
Load type: Inductor
Iphase: 404Arms
Twater: 18.6°C
Duration: 10sec
Test result:
Tcase of MOSFET: 45.9°C
Figure 35 shows the thermal distribution of power stage at 400Arms output with 10sec duration. The maximum
temperature rise was 45.9°C - 18.6°C = 27.3°C. As mention in 4.2.3, the junction temperature rise could be
47.3°C. When the temperature of coolant is 95°C, the junction temperature could be 142.3°C.
Application Note
34
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 35
Dynamic thermal distribution of the power stage @400Arms 10s
5.3.2.2
Bench test with 40Nm load
Test condition is shown as follow:
Vdc:
44.6V
Load type:
PMSM motor
Twater:
20°C
Motor Speed: 2000rpm
Torque:
Motoring 40Nm
Liquid flow:
15L/min
Duration:
10 seconds
Idc:
264A
Iphase:
339Arms
Figure 36 shows the related wave form of dynamic thermal distribution. DC voltage, DC current and phase
current could be read from the wave form.
Application Note
35
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 36
Test wave form of dynamic thermal distribution 40Nm motoring
C1: phase current signal from LEM sensor. C2: DC current. C3: DC voltage.
Figure 37 shows the result of dynamic thermal distribution at the end of test period. The positions of
measurement points SP1, SP2, SP3 SP4 are shown in Figure 37. SP1 is the highest temperature point of W phase
MOSFET. SP2 is the highest temperature point of V phase MOSFET. SP3 is the highest temperature point of U
phase MOSFET. SP4 is the temperature of DC-Link cap.
Note: the highest temperature point in the Figure 37 is the power terminal on the top left side. The reason is
that the power terminal surface is not smooth. The contact resistance is very high, but it wouldn’t influence the
measurement of MOSFET and DC-link capacitor.
Application Note
36
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 37
Dynamic thermal distribution of power stage 40Nm motoring
Figure 38 shows the dynamic behavior of the MOSFET and DC-link capacitor. The system started at 45 second. It
reached 40Nm at 1min05sec and kept to 1min15sec. At beginning the MOSFETs temperature is close to coolant
temperature, and the DC-link capacitor temperature is close to ambient temperature. The maximum
temperature rise of MOSFET case (∆Tc) is 24°C. The experimental analysis shows that the junction temperature
would be 20°C higher than top case temperature. When the coolant temperature is 95°C, the junction
temperature of MOSFET could be 140°C. This approximate equivalent meets the requirement. The DC-link
capacitor is quiet cool in this test because the thermal storage capacity is enough to handle the dynamic
thermal.
Application Note
37
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 38
Dynamic thermal behavior of the MOSFET and DC-link capacitor 40Nm motoring
5.3.2.3
Bench Test with 50Nm load
Test condition:
Vdc:
44.6V
Load type:
PMSM motor
Twater:
20°C
Motor Speed:
2000rpm
Torque:
Motoring 50Nm
Liquid speed:
15L/min
Current Sensor:
Panasonic +/-800A corresponding 0.5~4.5V
Duration:
0.5 seconds
Idc:
264A
Iphase:
480Arms
Figure 39 shows the related wave form of dynamic thermal distribution. DC voltage, DC current and phase
current could be read from the wave form.
Application Note
38
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 39
Test wave form of dynamic thermal distribution 50Nm motoring
C1: Phase current of current sensor (Yellow)
C2: DC current (Green)
C3: DC bus voltage (Purple)
Figure 40 shows the result of dynamic thermal distribution at the end of test period. The positions of
measurement points SP1 to SP7 are shown in Figure 40. SP1 is the highest temperature point of W phase
MOSFET. SP2 is the lowest temperature point of V phase MOSFET. SP3 is the highest temperature point of V
phase MOSFET. SP4 is the lowest temperature point of V phase MOSFET.SP5 is the highest temperature point of
U phase MOSFET. SP6 is the lowest temperature point of U phase MOSFET. SP7 is the temperature of DC-Link
cap.
Note: the highest temperature point in the Figure 40 is the power terminal on the top left side. The reason is
that the power terminal surface is not smooth. The contact resistance is very high, but it wouldn’t influence the
measurement of MOSFET and DC-link capacitor.
Application Note
39
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 40
Dynamic thermal behavior of the MOSFET and DC-link capacitor 50Nm mortoring
Sp1 Tmax of W Phase MOSFET, Sp2 Tmin of W Phase MOSFET, Sp3 Tmax of V Phase MOSFET
Sp4 Tmin of V Phase MOSFET, Sp5 Tmax of U Phase MOSFET, Sp6 Tmin of U Phase MOSFET
Sp7 Tmax of DC link capacitors
Figure 41 shows the dynamic behavior of the MOSFET and DC-link capacitor. The system started at
1min30second. It reached 50Nm at 2min03sec and shunt down immediately. At beginning the MOSFETs
temperature is close to coolant temperature, and the DC-link capacitor temperature is close to ambient
temperature. The maximum temperature rise of MOSFET case (∆Tc) is 30°C. The experimental analysis shows
that the junction temperature would be 20°C higher than top case temperature. When the coolant temperature
is 95°C, the junction temperature of MOSFET could be 145°C. This approximate equivalent meets the
requirement. The DC-link capacitor is quiet cool in this test because the thermal storage capacity is enough to
handle the dynamic thermal.
Application Note
40
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 41
Dynamic thermal behavior of the MOSFET and DC-link capacitor 50Nm motoring
5.4
Torque Speed characteristics
The inverter plus motor can reach the torque speed characteristics on the test bench as shown in Table 12 and
Table 13. It shows the BSG system capability. It is not directly limited by the power stage.
Table 12
Motoring characteristics
Motoring Speed (RPM)
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
Table 13
Torque Reference (Nm)
40
40
40
40
34
29
25
21
19
17
16
14
13
Torque measurement (Nm)
39.44
39.24
39.20
39.08
33.00
25.84
21.72
18.16
15.76
13.84
12.28
11.08
11.64
Generating characteristics
Generating Speed (RPM)
500
1000
1500
2000
2500
3000
3500
4000
Application Note
Torque Reference (Nm)
40
40
40
40
40
40
40
36
41
Torque measurement (Nm)
40.28
40.24
40.24
40.16
40.16
40.20
37.28
30.32
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Generating Speed (RPM)
4500
5000
5500
6000
5.5
Torque Reference (Nm)
32
29
26
24
Torque measurement (Nm)
24.72
20.48
17.40
14.08
Voltage ripple
The voltage ripple measured at 1750rpm of motor speed. The ripple is not the key parameter for Aluminum DC
link capacitors. If film cap is used for DC-link capacitor, the capacitance will significantly reduce. Then the
voltage ripple should be concerned. This test is archived for comparing with film cap.
Figure 42 to Figure 45 show the voltage ripple on DC bus as purple line C3 channel.
Table 14
Mode
Motoring
Motoring
Generating
Generating
Figure 42
Torque
16.5Nm
40.0Nm
16.5Nm
40.0Nm
Target Phase Current
160Arms
400Arms
160Arms
400Arms
Voltage ripple
1.63V
3.73V
1.79V
3.40V
Percentage
3.4%
7.8%
3.7%
7.1%
Voltage ripple waveform @ motoring 16.5Nm
Application Note
42
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
C1 and C2: VDS waveform of certain phase. C3: Voltage ripple of DC bus.
Figure 43
Voltage ripple waveform @ motoring 40Nm
C1 and C2: VDS waveform of certain phase. C3: Voltage ripple of DC bus.
Application Note
43
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 44
Voltage ripple waveform @ Generating 16.5Nm
C1 and C2: VDS waveform of certain phase. C3: Voltage ripple of DC bus.
Application Note
44
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Measurement results
Figure 45
Voltage ripple waveform @ Generating 40Nm
C1 and C2: VDS waveform of certain phase. C3: Voltage ripple of DC bus.
Application Note
45
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Summary
6
Summary
Electrical machines and inverters were used as Belt-driven Starter Generator (BSG) system in the Mild Hybrid
vehicle to enhance the output torque of the engine. A 48V 12kW inverter of BSG was designed with paralleled
TO-Leadless MOSFETs. The phase current was up to 500Arms while the VDS voltage spike was under 70V. The
maximum temperature rise of MOSFET was 30°C, and the current of MOSFET was balanced well. This design
fulfilled the power requirement with 105°C liquid cooling system. It’s scalable with optional numbers and
different RDSon of MOSFET in the same package and flexible for 3~6 phases inverter.
Application Note
46
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Reference
7
Reference
[1] Infineon AN2013-05 TO-Leadless: A new Package for High Current High Reliability Applications.
[2] Infineon Application Note: MOSFET Power Losses Calculation Using the Datasheet Parameters.
[3] Solder joint reliability against thermo-mechanical stress: Leadless packages for automotive MOSFET
Application Note
47
AN-Power stage of 48V BSG inverter
Reference design with TOLL & TOLG MOSFET
Table of Contents
Revision History
Major changes since the last revision
2018-08-2, V2.2 Add TOLG information.
Page or Reference
Description of change
Chapter 3.2.3
Add introduction of TOLG MOSFET
Chapter 3.2.3
Add available automotive TOLG MOSFET in the table
Chapter 4.2.5
TOLG MOSFET for Al based IMS board
Application Note
48
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