AN3338 datasheet(21/72 Pages) STMICROELECTRONICS

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AN3338

Electrical characteristics and functions

2.3.2

High voltage level shift

The built-in high voltage level shift allows direct connection between the low voltage control

inputs and the high voltage power half bridge in any power application up to 600 V. It is

obtained thanks to the BCD offline technology which integrates, in the same die bipolar

devices, low and medium voltage CMOS for analog and logic circuitry and high voltage

DMOS transistors with a breakdown voltage in excess of 600 V. This key feature eliminates

the need for external optocouplers, resulting in significant savings regarding component

count and power losses. Other advantages are high-frequency operation and short input-to-

output delays.

2.3.3

Undervoltage lockout

The SLLIMM supply voltage VCC is continuously monitored by an undervoltage lockout

(UVLO) circuitry which turns off the gate driver outputs when the supply voltage goes below

the VCC_thOFF threshold specified on the datasheet and turns on the IC when the supply

voltage goes above the VCC_thON voltage. A hysteresis of about 1.5 V is provided for noise

rejection purposes. The high voltage floating supply Vboot is also provided with a similar

undervoltage lockout circuitry. When the driver is in UVLO condition, both gate driver

outputs are set to low level, setting the half bridge power stage output to high impedance.

The timing chart of undervoltage lockout, plotted in

Figure 13, is based on the following

steps:

•

t1: when the VCC supply voltage raises the VCC_thON threshold, the gate driver starts to

work after the next input signal HIN/LIN is on. The circuit state becomes RESET.

•

t2: input signal HIN/LIN is on and the IGBT is turned on.

•

t3: when the VCC supply voltage goes below the VCC_thOFF threshold, the UVLO event

is detected. The IGBT is turned off in spite of input signal HIN/LIN. The state of the

circuit is now SET.

•

t4: the gate driver re-starts once the VCC supply voltage again raises the VCC_thON

threshold.

•

t5: input signal HIN/LIN is on and the IGBT is turned on again.

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