AN4043 datasheet(30/60 Pages) STMICROELECTRONICS

30 / 60 page

Electrical characteristics and functions

AN4043

30/60

Doc ID 022726 Rev 2

ADCs used in vector control applications have a typical full scale range (FSR) of about

3.3 V. The sense signals must be shifted and centered on FSR/2 voltage (about 1.65 V) and

amplified with a gain which provides the matching between the maximum value of the

sensed signal and the FSR of the ADC. Some typical examples of sense network sizing can

be found in the user manuals listed (see

References 5 and References 6).

2.3.11

Bootstrap circuit

In the 3-phase inverter the emitters of the low-side IGBTs are connected to the negative DC

bus (VDC-) as common reference ground, which allows all low-side gate drivers to share the

same power supply, while, the emitter of high-side IGBTs is alternately connected to the

positive (VDC+) and negative (VDC-) DC bus during the running conditions.

A bootstrap method is a simple and cheap solution to supply the high voltage section. This

function is normally accomplished by a high voltage fast recovery diode. The SLLIMM-nano

family includes a patented integrated structure that replaces the external diode. It is realized

with a high voltage DMOS driven synchronously with the low-side driver (LVG) and a diode

in series. An internal charge pump provides the DMOS driving voltage.

The operation of the bootstrap circuit is shown in

Figure 20. The floating supply capacitor

CBOOT is charged, from the VCC supply, when the VOUT voltage is lower than the VCC

voltage (e.g. low-side IGBT is on), through the bootstrap diode and the DMOS path with

reference to the “bootstrap charge current path”. During the high-side IGBT ON phase, the

bootstrap circuit provides the right gate voltage to properly drive the IGBT (see “bootstrap

discharge current path”). This circuit is iterated for all the three half bridges.

Figure 20.

Bootstrap circuit

The value of the CBOOT capacitor should be calculated according to the application

condition and must take the following into account:

●

voltage across CBOOT must be maintained at a value higher than the undervoltage

lockout level for the IC driver. This enables the high-side IGBT to work with a correct

gate voltage (lower dissipation and better overall performances). Please consider that if

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