在高边工作得MOSFET,其可能得失效模式和失效现象.docxVIP

Power MOSFET in High-Side Operating Modes, Possible Failure Modes, and Failure Signatures+ E+ X??n4 n k+ y, z. `! Z3 z: M nPower MOSFETs in high-side application can fail under any one of the following modes of operation:(a) High-impedance gate drive(b) Electro-static discharge (ESD) exposure2 B3 b- b5 D, G+ p+ D- f(c) Electrical over-stressed (EOS) operation9 k/ } ~4 l! f7 }! jIn most cases, failure analysis of the damaged MOSFET reveals a signature that can point towards a possible cause of failure.(a) High-Impedance Gate Drive4 f9 C/ ^; b6 _A generic schematic configuration for a high-side driver with inductive load is shown in figure 1. A typical gate drive design based on an application-specific integrated circuit (ASIC) caters to the primary gate charge requirements of the MOSFET, which are on the order of a few tens to hundreds of nanocoulombs. An effort to achieve high efficiency and optimize the integration of the ASIC results in low-current ( 50 μA) gate drives (V2 referenced to power supply ground) with a high output impedance ( 1 M?). This basically satisfies the total gate-charge requirements of the MOSFET.However, to avoid overloading the ASIC, the external gate resistor (R2) in such a design tends to have a high ohmic value (ranging from tens of ohms to several kiloohms). The feedback resistor (R3) also usually has a high ohmic value (ranging from several kiloohms to 1 M?). As a result, the source (S) of the power MOSFET (U1) is virtually floating.% Z; S E x??^3 C! j, y. R) b??E( sThe effect is magnified during turn-off and recirculation of the energy stored in the inductor (L1).. ~ Y2 { V8 c6 G# v! P9 E9 _??o P9 ~3 J* L?* w2 }1 H! y( ~, v; f* M# R0 N. H) `Fig. 1 - Typical High Side DriverThis approach fully satisfies the requirements for steady-state operation, where small amount of current, on the order of a few microamps, is all that is required to maintain the on state. But it can be inadequate for dynamic (transient) turn-on and turn-off operatio