ST AN1387 Application note

AN1387

APPLICATION NOTE

APPL ICATION OF A NEW MON OL IT HI C SM ART IG BT

IN DC MOTOR CONTROL FOR HOME APPLIANCES

A. Alessandria - L. Fragapane - S. Musumeci

1. ABSTRACT

This application notes aims to outline the characteristics of a new power device that joins the peculiarities

of an STMicroelectronics fast-switching PowerMESH™ IGBT with some novel protection features. A
driver circuit is integrated in the power device to implement over-current protection and soft thermal
shutdown. The current limitation also ensures a highly short-circuit rated device. Moreover the low
threshold voltage and inp ut current make it p ossible to drive the device directly from the output pin of a
microprocessor. The static and dynamic behavio r of the device will be illustrated and an applic ation will
be suggested.

2. INTRODUCTION.

In the last few yea rs IGB Ts have been appreciated in many appl ications in t he m id -power range, having
the advantage of bipolar conduction characteristics and insulated gate control. Efficient advances in
process and device technologies have improved conduction losses, working frequencies and
ruggedness under inductive load co nditions in hard switching applications. But nowada ys requirements
are becoming more and more stringent regarding ruggedness and reliability. On the other hand, the
planar technology is reaching its limit in terms of performance [1]. For this reason the monolithic
integration of protection features to prevent the intervention of faulty conditions represents a wi nning
choice in order to improve a device’s limits. Therefore the new trend in power semiconductor
manufacturers is to provide "system-on-chip" solutions [2].

Current literature proposes several sol utions in order to obtain an intelligent s witch in power conv ersion
applications, such as full-protected high voltage MOSFETs or IGBTs for automotive electronic ignition
[3,4]. But these solutions are not suitable for those applications in which conduction losses and switching
speed are both important. Indeed a Power MOSFET is good for high frequency applications, but at lower
current, while at the present time Smart IGB Ts are available only for low frequency applications, and the
research activities in the field of monolithic Smart IGBTs for fast-switching applications are really poor.
Hybrid solutions are actually available, but this approach has some drawbacks like package size,
complex assembly techniques and costs.

The device we are going to present (see figure 1) is very innovative in its product range, bec ause it
shows a high current density with switching performances that match well with the requirements of
applications like motor control drive systems, induction heating and SMPS.

November 2001

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AN1387 - APPLICATION NOTE

Figure 1: A Fast-Switching Smart IGBT

The proposed device is a new full-protec ted IG B T, packaged in a convenient three pin TO-220 package,

2

with an active area of about 12mm

, while the cont rol part occupi es an area of about 0.9mm2, including
the input pad and some trimming pads. Concerning the main electrical characteristics, the device has
600V of breakdown voltage and 10A of nomina l current. It is a logic level switch with a gate threshold
voltage of 1.5V and very low input current (1mA). These features allow direct driving from a micro

controller system. In this way STMicroelectronics’ intelligent switch is particularly suitable for motor
control in home appliances, consumer electronics and me dium power industri al servo-drive [5].

This paper will begin by giving some general information about the adopted technology and the static
and dynamic electrical characteristics of the device will then follow. In this context the dynamic
performances will be compared with the requirements of an experimental motor control application.

3. TECHNOLOGICAL OVERVIEW.

STMicroelectronics’ fast-switching Smart IGBT is manufac tured with a standard process based on its
patented strip horizontal layout. This layout consists of a p-type mesh implanted over an n-type epytaxial
layer. Some steps later n-type strips are then implanted over the p mesh to form the IGBT emitter. In
figure 2 the 3D view of the mesh layout is depicted, while in figure 3 the cross section of the strip layout
is shown.

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Figure 2: Mesh Overlay 3D View

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Figure 3: Strip Layout Cross Section

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AN1387 - APPLICATION NOTE

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This proprietary process improves switching performances and latch-up immunity, moreover the
introduction of gate fingers concur to reduce the gate internal resistance and to speed-up the device turn
off [6]. Furthermore a proprietary lifetime killing m ethod is performed implanting and diffusing platinum
ions.

The technology desi gn al lows to integrate in the same c hi p the Power IGBT and a s imple c ontrol ci rcuit.
This approach ensures a low-cost integration and a high value-added device, indeed only one
photolithography process is added to the standard process flow.

The control circuit is implemented with:

• N-MOS enhancement-mode transistor,

• polysilicon resist or s,

• polysilicon diodes.

The sign al MOSFET tra nsistors are im planted in the p -type mesh, whi le the polysilic on resistors an d

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