Graph 1: Simplifying heat is inserted unplug circuit

 

What should consider for FET above all is the puncture voltage with right choice, be voltage of the biggest input commonly 1.5 to 2 times. For example, 12V system is 25V or 30V FET normally, and 48V system is 100V normally or 150V FET is achieved below certain circumstance. The secure job area that next consideration element should be MOSFET (SOA) , if data expresses a medium curve. It is special conduce to demonstrative MOSFET be in short when how is thermal breakdown affected during power surge, this and the circumstance that unplugs must be absorbed in application is inserted to be not had in heat 2 send. Because safety operates area (SOA) it is to undertake choosing the most important level appropriately, consult please understanding MOSFET data is expressed – SOA graph, this article introduces TI how to undertake metrical in detail, generate the SOA of the MOSFET that shows in equipment data table next.

 

To stylist, crucial question is the electric current of the biggest surge that FET may endure (or predicting meeting restricts output) it is how old, and this kind of surge can last how long. Knew these news, can be in relatively simply the SOA that equipment data expresses searchs corresponding electric current and voltage difference on the graph.

For example, if design input voltage to be 48V, and hope inside 8ms limitation exports electricity do not exceed 2A, stylist can consult the 10ms curve of CSD19532KTT, CSD19535KTT and CSD19536KTT SOA (graph 2) , conclude two kinds of equipment after going out may be practicable, and CSD19532KTT is no good. Because CSD19535KTT has had enough surplus, to this kind of application, costlier CSD19536KTT may provide exorbitant performance.

 

Graph 2: The SOA of 3 kinds of different 100V D2PAK MOSFET

 

Assume environmental temperature is 25? C, as identical as the situation that measures SOA on data table. Because apply a likelihood finally to expose in hotter environment, so must according to environmental temperature and FET Wen Zhi of the biggest bear is compared, fall for SOA in proportion the forehead. For example, is the highest environment temperature of final system 70? C, can use formula 1 fall for SOA curve the forehead:

 

 

Below this kind of circumstance, the 10ms of CSD19535KTT, 48V ability will from? Does 2.5A fall to? 1.8A. Conclude from this give specific FET to may suit this application no longer, thereby stylist should reelect CSD19536KTT.

Notable is, this kind falls MOSFET of frontal method hypothesis is in next the biggest bear is lukewarm malfunctioning fitly, although normally won’t such. Does the invalidation place that measures in SOA test suppose happen in 200 actually? Below C or other and aleatoric higher temperature, calculative falls the specified number will be more adjacent and uniform. That is to say, this kind falls the computation of frontal method is not conservative algorithm.

 

SOA still will decide MOSFET encloses a type. D2PAK is enclosed can contain large silicon chip, so they are not constant popularity in the application of higher power. Lesser 5mm×6mm and 3.3mm×3.3mm all directions are compressed without down-lead (QFN) enclose suit low power application more. Be less than the surge electric current of 5 – 10A to resist, FET normally as compositive as controller together.

 

It is dot of a few attentions below:

 

Should insert in the light of heat unplug when application, to any circumstances that FET works in saturated area, stylist can use identical SOA to choose a course, can be power supply of net of OR-ing application, aether even (PoE) and low speed switch applies (if electric machinery is controlled) use identical FET to choose a method, during MOSFET closes, can appear the jackknife of quite tall VDS and IDS.

 

Heat is inserted unplugging is the application that a kind of apt uses the surface to stick outfit FET, is not via FET (enclose like TO-220 or I-PAK) . The reason heats in what happen at short pulse duration and thermal breakdown incident very finite. In other words, from silicon knot the component of capacitance thermal resistance to crust can prevent quantity of heat fast be lost arrives in circuit board or carbon fin with cooling node. The function of chip dimension – the knot is fought to the thermal resistance of crust (RθJC) very important, but enclose, circuit board and system come loose the function of hot environment – the knot is fought to environmental thermal resistance (RθJA) should small much. Stem from same reason, see carbon fin is used at these application very hard.

 

Design personnel often assumes the MOSFET of resistor of the lowest in catalog will have the strongest SOA. The logic of this backside is – inferior in same silicon chip production resistor makes clear normally enclose interior to have bigger silicon chip, this produced better SOA performance and smaller knot to heat up impedance to crust really. However, increased unit area resistance as the newer iteration of silicon chip (RSP) , silicon chip also apt increases batteries density. The unit structure of silicon chip interior is more concentrated, chip jumps over incidental thermal breakdown. Why do this have the old generation FET of taller resistor to also have the reason of better SOA function sometimes namely. Anyhow, investigate and compare SOA dispute to often be necessary.

 

Understand more in TI official net please all sorts of heat are inserted unplug the information of controller. The watch 1-3 key of article fine introduced to be used at heat to insert a few equipment that unplug, they offerred partial reference to be worth for SOA function.

 

More information consults please series of guest of MOSFET option rich.

 

Express 1: Use at 12V heat to insert the MOSFET that unplug

 

Express 2: Use at 24V heat to insert the MOSFET that unplug

 

Express 3: Use at 48V heat to insert the MOSFET that unplug