AN50014

Understanding the MOSFET peak drain current rating
Rev. 1.0 — 28 March 2022

application note

Document information
Information

Content

Keywords

MOSFET, maximum peak drain current

Abstract

This application note provides an explanation of the derivation of the maximum drain current as afunction of pulse duration rating.

AN50014

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Understanding the MOSFET peak drain current rating

1. Introduction
IDM is the maximum rated peak drain current for a power MOSFET. It can be defined as a functionof the time duration of a rectangular current pulse. IDM is referred to in the Nexperia applicationnote AN11158[1]

and IEC60747-8[2].

Recently, in some Nexperia MOSFET data sheets, a graph is included which shows the maximum
device peak drain current capability (IDM) expressed as a function of pulse duration. An example
from the BUK7S1R0-40H data sheet[3]

is shown below in Fig. 1.
aaa-033720

104
IDM
(A)

103

102

10
10-5

10-4

10-3

10-2

10-1

1

tpulse (s)10VGS = 10 V; Tmb = 25 °C; IDM is a single pulse
Fig. 1.

Maximum peak drain current capability as a function of pulse duration
In Fig. 1 time is shown logarithmically from 10 µs to 10 s. The maximum allowed peak drain current
IDM is also expressed logarithmically.
Historically the IDM capability is shown in the limiting values section of the data sheet for tp ≤ 10 µs.
ID at DC (continuous) is also shown. IDM is traditionally specified as four times the theoretical valueof ID at DC, see Fig. 2. The IDM rating here is more than four times the ID as the ID specified islimited by the package, rather than the silicon itself.

Table 5. Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134).
SymbolParameter

Conditions

Min

Max

Unit

VDS

drain-source voltage

25 °C ≤ T j ≤ 175 °C

-

40

V

VGS

gate-source voltage

DC; Tj ≤ 175 °C

-10

20

V

Ptot

total power dissipation

Tmb = 25 °C; Fig. 1

-

375

W

ID

drain current

VGS = 10 V; T mb = 25 °C; Fig. 2

-

325

A

IDM

peak drain current

pulsed; tp ≤10 µs; T mb = 25 °C; Fig. 3

-

1659

A

Fig. 2.

[1]

BUK7S1R0-40H data sheet limiting values
It is difficult for the user to know what the capability would be at other time durations. Some
information can be gleaned from the Safe Operating Area (SOA) graph, however it is still hard toassess the actual capability for different time intervals.
The aim of this new IDM graph is to provide information regarding the current handling capability of
the MOSFET for any time duration in the range provided. It should be noted that only the current
carrying capability due to conduction losses is considered. Additional losses incurred due toAN50014application note

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Understanding the MOSFET peak drain current rating
switching events (linear mode and avalanche) may take the device junction temperature beyond
the 175 ˚C limit and cause damage to the device.

2. IDM theoretical curve calculation
The power handling capability of the MOSFET can be derived using the transient thermal
impedance characteristic (Zth) curve. An example from BUK7S1R0-40H data sheet is shown in
Fig. 3 below:
aaa-028930

1

Zth(j-mb)(K/W)δ = 0.5
10-1

0.2
0.1
0.05

10-2 0.02

single shot

P

δ=

tp
10-3
10-6

Fig. 3.

10-5

10-4

10-3

10-2

10-1

tp
T

t
T
1

tp (s)BUK7S1R0-40H transient thermal impedance as a function of pulse duration
The transient power capability characteristic as a function of time can be determined, assumingthat the MOSFET junction temperature would be raised by 150 K, from 25 ˚C to 175 ˚C. See Eq. 1
and Fig. 4.

Pmax (t) =150
Zth(t)(1)

aaa-033423

105
P(max)
(W)
104

103

102

10
10-5

Fig. 4.

10-4

10-3

10-2

10-1

1

tp (s)

10

Peak power capability as a function of pulse duration

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Understanding the MOSFET peak drain current rating
To relate power capability to theoretical maximum current, the following relationship is used:

I DM (t) =Pmax (t)
RDSon

(2)

RDSon in Eq. 2 is the maximum value specified at 175 ˚C. Using the data sheet value of 2.2 mΩ, atheoretical characteristic based on this formula is shown in Fig. 5.
aaa-033449

104

IDM
(A)

103

102
10-5

Fig. 5.

10-4

10-3

10-2

10-1

1

tp (s)

10

Peak current capability as a function of pulse duration; calculated values
The maximum theoretical device current for a 10 µs pulse is 2.3 kA, see Fig. 5. However, the RDSonchanges with ID and this is not taken into account with this approach. RDSon value increases with ID.
See the example graph from BUK7S1R0-40H data sheet in Fig. 6 below:

RDSon
(mΩ)

aaa-028934

4
4.5 V

3.2
5V

2.4
6V

1.6

0.8

0

7V

5.5 V

VGS = 10 V

0

80

160

240

320
ID (A)

400

Tj = 25 °C
Fig. 6.

BUK7S1R0-40H drain-source on-state resistance as a function of drain current;
typical values

The data provided in Fig. 6 is for 25 °C and is only for ID up to 400 A. Therefore, it cannot be used
for IDM estimation. As RDSon dependence on ID is not taken into account, the data on Fig. 5 isan over estimate. Actual measurement of the device capability is a better way to determine withconfidence the current handling capability at various time intervals.

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Understanding the MOSFET peak drain current rating

3. Device test method
Devices at Nexperia are measured for IDM from 10 µs pulses up to DC. The devices, depending on
their size, are expected to achieve several thousand of Amperes of IDM at 10 µs and few hundred
Amperes at DC. For this reason different test gear is used for pulsed and DC measurements.
For pulsed conditions, an in-house designed pulse current tester is used, capable of 5 kA for pulse
lengths up to 100 µs. The longest pulse tested is 10 ms. The device is mounted to a speciallydesigned test PCB which ensures low inductance and current. This is important because thepulsed current will have very steep turn-on and turn-off slopes. The thermal capability of the PCB isnot critical since at such short pulse intervals no significant heat is transferred to the PCB.
Waveforms showing typical behaviour are shown in Fig. 7 below:
aaa-033453

2,500

25
VDS, VGS
(V)

ID
(A)

20

2,000
ID

15

1,500
VGS

10

1,000

VDS

500

0

Fig. 7.

0

40

80

5

120

time (µs)

1600Drain current, drain-source and gate-source voltages as a function time

In this example a 1,500 A, 100 µs pulse is applied to a device which is already switched on.
Initially the voltage drop across the device is around 2.7 V, therefore RDSon is around 1.8 mΩ(2.7 V/1,500 A). At this, initial instance the junction can be considered to be close to 25 °C ambient
temperature. According to the device data sheet, at 25 °C the maximum value of RDSon is 1 mΩ
at a 25 A test current and the typical value is 0.88 mΩ. As it can be seen in this example, themeasured RDSon is roughly double the data sheet value, because of the big difference in theapplied current.
As the device heats up, the VDS increases to around 7.5 V. RDSon is therefore around 5 mΩ
(7.5 V/1,500 A). This waveform is recorded just before device failure, so it is likely that the junction
temperature was higher than 175 ˚C. It may happen that the capability of the device exceeds
the tester capability, so the device cannot be tested until destruction, and the true IDM cannot be
obtained.
A different tester is used to test DC capability, because the device has to be cooled. The mounting
base temperature is kept as close to 25 ˚C as it is practically possible, whilst the junction
temperature achieves 175 ˚C. The device must be mounted on a special high thermal conductivity
board, in order to ensure that heat is removed from the package as effectively as possible. The
device and PCB are then immersed in cooling fluid. Note that these measures to cool the device
are required to demonstrate the MOSFET capability and are impractical for most real applications.
Several devices are tested at each time point (from 10 µs to DC). This allows statistical analysis tobe performed and suitable derating applied to take into consideration device variability.

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Understanding the MOSFET peak drain current rating

4. Measurement results
For this device (BUK7S1R0-40H) the theoretical ID(dc) is 414.75 A. Therefore IDM at 10 µs is
determined as per the convention: 4 × 414.75 = 1,659 A.

aaa-033450

104

IDM
(A)

103

conventional data sheet
value = 4 × 414.75 = 1,659 A

102
10-5

10-4
maximum values

Fig. 8.

10-3

10-2

minimum values

10-1
theoretical values

1
conventional value

tp (s)

10

Peak drain current as a function of pulse duration; measured and calculated values
Considering a small sample of measured devices, IDM at 10 µs achieves around 2.1 kA. As
previously suggested, this is less than the value derived on Fig. 5 of 2.3 kA. Fig. 8 demonstrates
the relationship between the theoretical and measured values for IDM. The grey triangle denotes
the value obtained by convention.

Derating
To guarantee a safe capability curve the measured values are derated by 20%, to consider the factthat Tj will be > 175 ˚C in the measurements and that there will be some batch to batch variation in
device performance. The derated peak current at 10 µs is, therefore, reduced to 1,680 A, which is
close to the conventionally obtained value. At the DC end of the curve, devices can be measured
for 10 s or longer durations, however there is still an untested gap between 10 ms and 10 s. To fillthis gap interpolation is used, with the value obtained for 10 s used for the 1 s value.

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Understanding the MOSFET peak drain current rating
aaa-033451

104

IDM
(A)

103

102
10-5

10-4

10-3

maximum values
minimum values

Fig. 9.

10-2

10-1

1

tp (s)

10derated values
theoretical values

Peak drain current as a function of pulse duration; derated values
Consequently, the characteristic curve is a theoretical line which is supported by test results. If thederated minimum measured values are above the theoretical line then the theoretical line is thelimit, otherwise the derated measurement point will determine the characteristic; see Fig. 10

aaa-033452

104

IDM
(A)

103

102
10-5

10-4
maximum values
minimum values

10-3

10-2
derated values
theoretical values

10-1

1

tp (s)

10data sheet values

Fig. 10. Peak drain current as a function of pulse duration; data sheet values
Having determined the capability at different pulse durations, this is aligned with other data sheet
characteristics such as the Safe Operating Area, example in Fig. 11 below:

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Understanding the MOSFET peak drain current ratingID(A)

aaa-028929

104

Limit RDSon = VDS / ID

103

tp = 10 µs
DC102

100 µs

10
1 ms
10 ms
100 ms

1
10-1

1

10

VDS (V)102

Tmb = 25 °C; IDM is a single pulse
Fig. 11. BUK7S1R0-40H Safe operating area; continuous and peak drain currents as a function of drain-source
voltage

5. Example of the final IDM curve
The graph shown in Fig. 12 shows the capability of the BUK7S1R0-40H , taking into account thetheoretical capability and de-rated measured capability. Fig. 12 also shows a 10% safety line fromthe measured data points, that is also taken into account when producing the final graph thatappears in the data sheets. Due to the combination of the methods for obtaining the data sheet
values, Nexperia has a high degree of confidence that this is the practical limit for current handlingcapability as a function of time.
10

aaa-034161

4

I DM
(A)

10

3

I

DM

at 10 µs

is 4 × I D(dc)10

50 µs and 100 µs
derated by 20% frommeasured values

2

10

-5

10

-4

measured values

10

-3

10
10% line

-2

10

-1

theoretical model

1
final grapht p (s)10

VGS = 10 V; Tmb = 25 °C; IDM is a single pulse
Fig. 12. BUK7S1R0-40H peak drain current capability; measured values, theoretical model, 10% line and finalgraph

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Understanding the MOSFET peak drain current rating

6. References
1. Nexperia application note AN11158
2. IEC IEC 60747-8: 2010
3. Nexperia data sheet BUK7S1R0-40H

7. Revision history
Table 1. Revision history
Revision
Date
numberDescription

1.0

Initial version.

2022-03-28

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for the products described herein shall be limited in accordance with theTerms and conditions of commercial sale of Nexperia.
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Understanding the MOSFET peak drain current rating

List of Tables
Table 1. Revision history......................................................9AN50014application note

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Understanding the MOSFET peak drain current rating

List of Figures
Fig. 1. Maximum peak drain current capability as afunction of pulse duration.....................................................2
Fig. 2. BUK7S1R0-40H data sheet limiting values...............2
Fig. 3. BUK7S1R0-40H transient thermal impedanceas a function of pulse duration............................................ 3
Fig. 4. Peak power capability as a function of pulse
duration.................................................................................3
Fig. 5. Peak current capability as a function of pulse
duration; calculated values.................................................. 4
Fig. 6. BUK7S1R0-40H drain-source on-state
resistance as a function of drain current; typical values.......4
Fig. 7. Drain current, drain-source and gate-source
voltages as a function time.................................................. 5
Fig. 8. Peak drain current as a function of pulse
duration; measured and calculated values.......................... 6
Fig. 9. Peak drain current as a function of pulse
duration; derated values...................................................... 7
Fig. 10. Peak drain current as a function of pulse
duration; data sheet values..................................................7
Fig. 11. BUK7S1R0-40H Safe operating area;
continuous and peak drain currents as a function ofdrain-source voltage.............................................................8
Fig. 12. BUK7S1R0-40H peak drain current capability;
measured values, theoretical model, 10% line andfinal graph............................................................................ 8AN50014application note

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Understanding the MOSFET peak drain current rating

Contents
1. Introduction................................................................... 2
2. IDM theoretical curve calculation................................. 3
3. Device test method...................................................... 5
4. Measurement results....................................................6
5. Example of the final IDM curve................................... 8
6. References.................................................................... 9
7. Revision history............................................................9
8. Legal information........................................................10© Nexperia B.V. 2022. All rights reserved

For more information, please visit: http://www.nexperia.com
For sales office addresses, please send an email to: salesaddresses@nexperia.com
Date of release: 28 March 2022

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