Application Note ANPS073E, V1.0, July 2004 Calculated Datasheet Parameter ISO-Nominal Load Current and Total Power Dissipation in HITFET® and PROFET® Datasheet Automotive Power N e v e r s t o p t h i n k i n g . ISO-Nominal Load Current and Power Dissipation Edition 2004-07-07 Published by Infineon Technologies AG, St.-Martin-Strasse 53, D-81541 München, Germany © Infineon Technologies AG 7/19/04. All Rights Reserved. Attention please! The information herein is given to describe certain components and shall not be considered as warranted characteristics. Terms of delivery and rights to technical change reserved. We hereby disclaim any and all warranties, including but not limited to warranties of non-infringement, regarding circuits, descriptions and charts stated herein. Infineon Technologies is an approved CECC manufacturer. 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Application Note ANPS073E 2 V1.0, 2004-07-07 ISO-Nominal Load Current and Power Dissipation Introduction 1 Introduction The Hitfet and Profet are power-MOSFET devices with integrated protection functions. In order to ensure a long lifetime the application should be designed in a way that overload conditions does not occur or are at least minimized. Therefore the power MOSFET devices Hitfet and Profet offer integrated protection functions. Under fault conditions, for example over temperature, overload or short circuit, the integrated protection will turn off the device. Of course this unwanted turn off can cause a malfunction of the application. The unwanted turn off due to over temperature or overload can be avoided by choosing a lower ohmic device. In order to simplify this selection process the data sheets show the values ISO load current ID(ISO) and Nominal load current ID(Nom). One other parameter for simplifying the device selection is the value of power loss Ptot. 2 Definition The ISO current approach considers the thermal resistance between Junction and Lead frame RthJC as shown in Figure 1. This assumes the lead frame as an isothermal area with the temperature tambient=85°C. Under this conditions the ISO current is calculated in a way that the voltage drop between Drain and Source becomes maximal VDS=0.5V. If this current leads to a junction temperature of TJ>150°C then the ISO current is reduced to become TJ=150°C. The ISO current is interesting for devices directly mounted to the heatsink, but not for surface mounted devices (SMD) on a printed circuit board (PCB), because the thermal resistance between Junction and Case RthJC is used. The difference of the nominal load current ID(Nom) is that this approach considers the thermal resistor between Junction and Ambient RthJA. Under this conditions the nominal load current is the current which meets both following conditions. First this current will heat up the junction to TJmax=150°C and second the voltage drop will be limited to VDS≤0.5V. TJ T C=Tambient = const Chip Case TA Chip RthJC Case RthJA PCB ISO_vs_Nom.emf Figure 1 Device with constant Case temperature versus device on PCB related to ambient temperature. Application Note ANPS073E 3 V1.0, 2004-07-07 ISO-Nominal Load Current and Power Dissipation Computation 3 Computation Since the data sheet parameters Nominal load current and ISO load current are calculated values which can not be tested directly during production this application-note will describe how this parameters are calculated. The computation process for the ISO load current is shown in Figure 2. Starting with the ambient temperature the RDS(on) is calculated. The ISO definition allows a voltage drop of 0.5V, which gives the current. Via the on-state-losses the junction temperature TJ comes out. This process is repeated until there is no more change in the junction temperature. If now the calculated junction temperature is below the maximum allowed value TJmax the ISO current is the value from the last iterative step. If the junction temperature is above the maximum allowed value then the ISO current is calculated from the maximum allowed power loss at TJmax. The nominal load current is calculated in a similar way, as shown in Figure 3. After the temperature dependent RDS(on) is calculated two currents will be taken into account. The first current is the value coming from 0.5V voltage drop. The second value is given by the maximal power loss at the given Junction temperature. The lowest of this two values is chosen as nominal load current ID(Nom). Via the on-state-losses the new junction temperature TJ is calculated. This process is repeated until there is no more change in the junction temperature. The parameter Ptot is also a calculated value. It shows the maximum allowed on state loss for a constant Case temperature TC. Therefore the thermal resistance RTHJC is used. The formula is T JCmax – T C P tot = ----------------------------R thJC Application Note ANPS073E 4 V1.0, 2004-07-07 ISO-Nominal Load Current and Power Dissipation Computation TJ (n ) = Tambient TJ ( n −1) = TJ (n ) RDS ( on ) = f (TJ (n ) ) I D ( ISO ) = 0.5V RDS ( on) 2 Pon = I DISO ⋅ RDS ( on ) TJ (n ) = Tambient + Pon ⋅ RthJC No TJ (n ) = TJ ( n −1) ? Yes Yes TJ (n ) < TJ max ? No I D ( ISO ) Figure 2 I D ( ISO ) = TJ max − Tambient RthJC ⋅ RDS (on ) (TJ max ) IDiso.emf Iterative computation process for ID(ISO) current Application Note ANPS073E 5 V1.0, 2004-07-07 ISO-Nominal Load Current and Power Dissipation Computation TJ ( n ) = Tambient TJ ( n −1) = TJ (n ) RDS ( on ) = f (TJ (n ) ) I1 = I2 = 0.5V RDS ( on ) TJ max − Tambient RthJA ⋅ RDS (on ) I DNom = Min(I1 , I 2 ) 2 Pon = I DNom ⋅ RDS ( on ) TJ (n ) = Tambient + Pon ⋅ RthJA No TJ ( n ) = TJ ( n −1) ? Yes I DNom IDnom.emf Figure 3 Iterative computation process for Nominal load current ID(Nom) Application Note ANPS073E 6 V1.0, 2004-07-07 ISO-Nominal Load Current and Power Dissipation Revision History: 2004-07-07 Previous Version: none Page V1.0 Subjects (major changes since last revision) We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: [email protected] Application Note ANPS073E 7 V1.0, 2004-07-07 http://www.infineon.com Published by Infineon Technologies AG