500V CoolMOS

7

Application Note AN 2012-04

V1.0 April 2012

Figure 2: cross section of standard MOSFET (left) and SJ MOSFET (right) [5]

“The SJ principle gives us the opportunity to create best-in-class types, which have not been possible before

such as a 100 mΩ/600V part in a TO-220 package. Furthermore it allows making parts with very low

Both input and high voltage level of the output capacitance scale directly with the chip size, whereas reverse

capacitance and to some extent the low voltage level of the output capacitance is technology dependent.

Characteristic of all Superjunction devices is a strong non-linearity of the output capacitance with high values

at low voltage and low values at high voltage. This behavior can be easily understood if you take into

account that the output capacitance is proportional to the area of the blocking pn-junction and inverse

proportional to the width of the space charge layer (or the voltage sustaining area). At low voltage the p-

columns are not depleted and form a very big surface, furthermore the width of the space charge layer is

very narrow (the white area seen in

” Figure 2). ” At high voltage however the p-columns are fully depleted

and the space charge layer has reached its full

extension of roughly 45μm for a 600V device. Important is

that the non-linearity of the output capacitance allows a quasi zero-voltage-switching (ZVS) turn-off of the

device, lowering turn-off losses. Superjunction devices are by nature fast in switching. Very small

capacitances together with a low gate charge make rise and fall times of a few nanoseconds a reality.

” [5]

For more information on Superjunction

devices please read the article “Mastering the Art of Slowness” which

is available on www.infineon.com.

2.2

Superjunction Benefit of 500V CE

Chapter 2.1 illustrated the general characteristics of a SJ MOSFET in comparison to a standard MOSFET.

N

ow the question arises “What is the benefit for the 500V CE?” This application note will describe two of the

most important factors starting with the switching speed.

2.2.1 Switching Speed

As mentioned in the general description the switching speed increases dramatically. This behavior comes

from the low parasitic capacitances of a SJ MOSFET in comparison to the standard MOSFET. A SJ

MOSFET has about half of the value of input and output capacitance, which brings the benefits for switching

losses and driving losses. Figure 3 represents these parasitic capacitances (marked in red) in a simplified

schematic.