The Influence of Parasitic Inductance on Current Mismatch in Parallel MOSFETs
In order to produce designs that satisfy the current demands of the Personal Computer (PC) industry,engineers have resorted in many cases to paralleling MOSFETs to reduce the losses and increase the power converters efficiency. Traditionally, this has been an easy decision to make since the switching frequency and the switching speeds were kept low and the current sharing between the paralleled MOSFETs depended mainly upon the ratios of the device On-Resistance RDS(ON). With the immergence of the modern high frequency fast switching Pulse Width Modulation (PWM) ICs and MOSFETs, we believe that this decision must be taken with greater care to achieve the same desirable results we came to expect and achieve. In this paper we will show that there are several conditions that must be met to achieve a successful, reliable and robust design.We will also show some of the pitfalls that may lead to unbalanced current sharing and unbalanced sharing of dynamic losses causing excessive power dissipation and poor reliability or even worse, leading to failure of the device with the most stresses. The analysis will be carded out using Worst Case conditions and also some Extreme Value Analysis will be conducted to allow us to understand the potential rare problems that may be encountered when a company manufactures several million MOSFET parameters that ultimately determine the losses in a set of paralleled devices are:1. The device On-Resistance RDS(ON).2. The Gate threshold voltage Vgth3. The device and package Source lead inductance4. The device and package Gate lead inductanceLets now consider the gate threshold voltages effect on current sharing. In a typical case of a MOSFET, Vgth has a maximum value of 3 Volt and a minimum value of 1V. It is clear that if two devices are connected in parallel one has a Vgth =1V and the other has a Vgth =3V, and they are both driven from the same Gate Driver, the MOSFET that has the lower Vgth will conduct first hogging an disproportionate share of the dynamic losses.
Alan Elbanhawy
Fairchild Semiconductor
国际会议
PCIM China 2006(International Conference Power Electronics)(2006年中国电力电子技术国际会议)
上海
英文
63-67
2006-03-21（万方平台首次上网日期，不代表论文的发表时间）