Power Matters.TM
Improving the Performance of your
DC-DC Forward Converter using
I2MOSTM MOSFET Technology
Microsemi Space Forum 2015
Al Ortega, Marketing Manager
© 2015 Microsemi Corporation. Company Proprietary
1
Contents
I2MOS Advantages
Single Event Effect Tests
DC- DC Design performance advantages
• Efficiency
• Avalanche Energy
Summary
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2
I2MOS advantages
Highest available SEE performance, 85- 90 MeV at full rated BVDss
Highest Avalanche capability: 5X greater than competition
TID (Total Ionizing Dose) Rating: 100Krad- 500Krad (depending on
specific device)
Commerce Rating: 9A515.e
• Most Euro countries will not need a license!
Competitive pricing on new designs
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I2MOS FOM versus Competition
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SEE results- Microsemi vs. Competitor
SEE Response - R6,150V,N,MR
175
150
Bias VDS (Volts )
125
Kr Ion;
LET=39±5%;
50±5%µm;
410±5%MeV
Xe Ion;
LET=61±5%;
66±7.5%µm;
825±5%MeV
100
75
50
25
0
0
-5
-10
-15
-20
Au Ion;
LET=90±5%;
80±5%µm;
1470±5%MeV
Bias
VGS
(Volts)
-25
SEE Response - R6,200V,N,MR
225
200
175
150
125
100
75
50
25
0
Bias VDS (Volts )
Xe Ion;
LET=42±5%;
205±5%µm;
2450±5%MeV
Xe Ion;
LET=61±5%;
66±7.5%µm;
825±5%MeV
0
-5
-10
-15
-20
IR (R6)
-25 Bias VGS (Volts)
Microsemi (I2MOS)
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I2MOSTM MOS P/N Structure
MRH
BVDSS/1
Channel ID @ 25C
0
(V)
MRH
20
Package
Screening
RAD LEVEL
U3
S
R
R= 100K
F= 300K
G= 500K
(A)
N
22
Microsemi 20= 200V
N
U3= SMD0.5
S= JANS
Rad- Hard 10= 100V
P
T2= TO- 39
V= JANTXV
13= 130V
T3= TO- 257
C= EDU
06= 60V
U5= LCC-18
03= 30V
C= die
MOSFET
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I2MOSTM Planned Products
Phase 1: I2MOSTM portfolio, N- Ch, Sz 3
Bvdss
(V)
Similar
JEDEC
Number
Industry
Equivalent
MSC p/n
150
200
250
2N7589U3
2N7591U3
2N7593U3
IRHNJ67134
IRHNJ67230
IRHNJ67234
MRH15N19U3
MRH20N16U3
MRH25N15U3
SMD0.5
Phase 2: I2MOSTM portfolio, N- Ch, Sz 5.5
Bvdss
(V)
Similar
JEDEC
Number
150
150
200
200
250
250
2N7582T1
2N7581U2
2N7584T1
2N7583U2
2N7586T1
2N7585U2
Industry Equivalent RH2 Base MSC p/n Package
IRHMS67164
IRHNA67164
IRHMS67260
IRHNA67260
IRHMS67264
IRHNA67264
MRH15N45T1
MRH15N56U1
MRH20N45T1
MRH20N56U1
MRH25N45T1
MRH25N56U1
TO-254
SMD-2
TO-254
SMD-2
TO-254
SMD-2
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TO-254
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7
Efficiency Performance of I2MOS
DC-DC Forward Converter (Resonant Reset Topology)
MRH25N15U3 vs. IRHNJ67234
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DC-DC Criteria
Create a Circuit to Reveal Differences in MOSFET Power
Losses
Parallel-Inductor Isolated Forward DC-DC Converter
Improved Efficiency
• Resonant Transformer Reset
• Lower DC Losses in Inductors and Schottky Rectifiers
Use Vdd = 50Vdc
• Peak of Resonant Reset Voltage Will Be: Vdd + (Id(pk) * Lm / Cr)
– Lm is Power Transformer Magnetizing Inductance (~120uH)
– Cr is the Resonance Capacitance = Coss || Cj (Ns/Np) * (~810pF)
– Worst Case Resonance Peak at fsw = 350kHz and Vout = 5.0Vdc (~120Vpk)
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Efficiency Test Criteria
Voltage De- Rating= 50%
• Use Microsemi MRH25N15U3 and IR IRHNJ67234, 250V devices.
(200V Device May Be Used For Higher Efficiency With Lower Voltage
Margin.)
100W Maximum Output Power
• 20A Maximum Output Current
– 66W For Vout = 3.3Vdc
– 100W For Vout = 5.0Vdc
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Efficiency Test Circuit Schematic
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Efficiency Test Circuit Features
Circuit Used For Power Switch Efficiency Comparison:
• Circuit Uses U3 Packages For All Power Functions
– Small Size
– Ease of Thermal Management
• Output Uses Paralleled Output Stage For Increased Efficiency
– Schottkies and Inductors Share Current ~50:50
– DC Power Losses Reduced by ~1/4 - 1/3!
•
•
•
•
Optimized for 3.3Vdc < Vout < 5Vdc
Optimized For 1A < Iout < 20A
Optimized For 350kHz < fsw < 500kHz
Uses COTS Micrel MIC4424 Gate Driver IC
– Rad-Hard Equivalents Available from Intersil
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Efficiency Test Parameters
DC Output (Vout) Set By Varying Input Duty Cycle
• Duty Cycle = Desired Vout * (Ns/Np) / Vdd
Efficiency:
h = Pout / (Pin + Pbias) = (Vout * Iout) /((Vdd * Idd) + (Vbias * Ibias))
Iout = Set, Varied from 1A to 20A
Vdd = Set, Constant = 50Vdc
Vbias = Set, Constant = 12Vdc
Vout is Set By Varying the Input Duty Cycle
Idd and Ibias Are Measured at Each Operating Point
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MOSFET Losses
Key Contributors to Power MOSFET Switch Losses:
• DC Losses: Id(rms)2 * Rds(on) * D
• AC Losses: Gate + Switching
– Gate Input Losses: Qgt * Vbias * fsw
– Drain Switching Losses: ~ Vdd * Id(rms) * (tr + tf) * fsw / 2)
+ (Coss * Vdd2 * fsw)
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Forward Converter Design Parameters
Duty Cycle = D = (Vout / Vin) * (Ns / Np) = ton / toff
Id(pk) = (Id(avg) / D) + (0.5 * (Vdd * ton) / Lm)
Vres(pk) = Vdd + Id(pk) * (Lm / Cr)0.5
tres = p * (Lm * Cr)0.5
Cr = Coss + (Cj / (Np/Ns))
• Cj is the Output Schottky Junction Capacitance
Vds (V)
Vres(pk)
Vdd
0
Id (A)
ton
tres
time
toff
Id(pk)
Id(avg)/D
0
time
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Measured Drain-Source Voltages
Vout = 5.0Vdc, Iout = 1Adc, fsw = 350kHz
Vout = 5.0Vdc, Iout = 20Adc, fsw = 350kHz
VDS(pk) = 122V
VDS(pk) = 148V
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Efficiency Parameters
From Data Sheet Parameters:
• Rds(ON)
– MRH25N15U3 – 175mW max.
– IRHNJ67234 – 210mW max.
– IR Device 20% Higher Than Microsemi
• Qgt
– MRH25N15U3 – 32nC typ. (est. 40nC max.)
– IRHNJ67234 – 50nC max. (est. 40nC typ.)
• Coss
– MRH25N15U3 – 275pF typ.
– IRHNJ67234 – 187pF typ.
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Efficiency Data- +3.3Vout, 350 Khz.
100W Forward Converter Efficency: Vdd = 50Vdc, Vout = 3.3Vdc, fsw =
350kHz
84%
Conversion Efficiency
82%
80%
78%
76%
MRH25N15U3
IRHNJ67234
74%
72%
0
5
10
15
20
Output Current (Adc)
At higher currents the improvement in conduction
losses provide an advantage.
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Efficiency Data, Vout = 5.0V, 350 Khz.
100W Forward Converter Efficency: V dd = 50Vdc, Vout = 5.0Vdc, fsw = 350kHz
88%
Conversion Efficiency
86%
84%
82%
80%
MRH25N15U3
IRHNJ67234
78%
76%
0
5
10
15
20
Output Current (Adc)
At higher currents the improvement in conduction
losses is slightly better at 5.0Vout vs. 3.3Vout.
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Efficiency Data, +3.3Vout, 500 Khz.
100W Forward Converter Efficency: Vdd = 50Vdc, Vout = 3.3Vdc, fsw = 500kHz
84%
Conversion Efficiency
82%
80%
78%
76%
MRH25N15U3
IRHNJ67234
74%
72%
0
5
10
15
20
Output Current (Adc)
At 500 Khz. There are more switiching losses in both
parts but I2MOS part maintains the advantage.
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Efficiency Data, 5.0Vout, 500 Khz.
100W Forward Converter Efficency: V dd = 50Vdc, Vout = 5.0Vdc, fsw = 500kHz
88%
87%
Conversion Efficiency
86%
85%
84%
83%
82%
81%
MRH25N15U3
IRHNJ67234
80%
79%
78%
0
5
10
15
20
Output Current (Adc)
Efficiency improvements @ higher currents when
Vout = 5.0V
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Vds (V)
VBR(DSS)
Vdd
0
Id (A)
ton
tav
time
Id(pk)
0
time
Avalanche Energy Performance
MRH25N15U3 vs. IRHNJ67234
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Avalanche Basics
Avalanche Performance Indicates
VBR(DSS)
Vds (V)
Ruggedness of MOSFET
• Energy Handling Capability
– Repetitive
– Single Pulse
– Specified in Joules (V * I * t)
“Unconstrained” Inductors Cause
Vdd
0
ton
Id (A)
Excursions to VBR(DSS)
• Energy ~ (L * Id(pk)2 / 2) * (1 – (Vdd
/ VBR(DSS))
• Junction Dissipates Enormous
Instantaneous Power
– If VBR(DSS) = 250V and Id(pk)
= 10A, Pinst = 2500W!
Vds
“Ringout”
Due to
Residual
Energy in L
and L-Coss
Resonant
Circuit
tav
time
Id(pk)
0
time
The Greater the Avalanche Energy
Rating, The Better
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Data sheet Specs & Avalanche Test Circuit
Part #
Eas
Ear
MRH25N15U3 15 mJ
300 mJ
IRHNJ67234
56 mJ
7.5 mJ
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Avalanche Test PCB
Board Size = 5.8 x 4.1 x 0.063”, 4 Layer FR-4, Double Sided
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Avalanche Test Procedure
VBR(DSS)
1. Turn ON Device Under Test (DUT)
Ramp Inductor Current to Desired Id(pk) during
ON Time (ton)
Id(pk) = Vdd * ton / L
Vds (V)
Avalanche Test Has Two Regions:
Vds “Ringout”
Due to
Residual
Energy in L
and L-Coss
Resonant
Circuit
Vdd
0
2. Turn OFF DUT
ON Time Adjusted to Obtain Desired Id(pk)
and Thus Eav
ton
Id (A)
Drain Voltage “Flys” to VBR(DSS)
Avalanche Time (tav) = L * Id(pk) / (VBR(DSS) – Vdd)
Avalanche Energy (Eav) = VBR(DSS) * Id(pk) * tav
time
tav
Id(pk)
0
time
Ideal Waveforms
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Measured Avalanche Performance
MRH25N15U3, 7.5mJ
VBR(DSS) = 283V, Id(pk) = 12A, ton = 29.5us
MRH25N15U3, 15mJ
VBR(DSS) = 304V, Id(pk) = 11A, ton = 71.5us
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Measured Avalanche Performance
MRH25N15U3, 300mJ
VBR(DSS) = 314V, Id(pk) = 15A, ton = 750us
MRH25N15U3, 300mJ (Expanded)
VBR(DSS) = 314V, Id(pk) = 15A, ton = 750us
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Measured Avalanche Performance
IRHNJ67234, 7.5mJ
VBR(DSS) = 300V, Id(pk) = 10A, ton = 24.5us
IRHNJ67234, 56mJ
VBR(DSS) = 302V, Id(pk) = 16.7A, ton = 120us
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Summary
Efficiency
Avalanche Capability
MRH25N15U3 Demonstrated More
Efficient Than IR IRHNJ67234
• By up to 2.75%
MGN25N15U3 Efficiency holds up over
the full current range of 5A – 20A.
Especially at higher load currents
Microsemi MRH25N15U3
Demonstrated 2X Repetitive
Avalanche Capability Over IR
IRHNJ67234
Microsemi MRH25N15U3
Demonstrated 5.4X Single Event
Avalanche Capability Over IR
IRHNJ67234
IRHNJ67234 Efficiency decreases due
to higher conduction Losses
• Useful Output Current Range Must
Be De-Rated to 18A
Increased Losses Mean More
Aggressive Thermal Management
Required (Bigger Heat Sink for Lower
qJA)
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Thank You
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