AN2738 datasheet(21/54 Pages) STMICROELECTRONICS

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AN2738

Application example

Doc ID 14589 Rev 2

21/54

Application example

A typical scheme for a 3-phase inverter application is shown in Figure 18. In order to drive a

3-phase load as for example a BLDC or Induction AC motor, three L6390 ICs can be used.

Figure 18.

3-phase drive- typical scheme

Each L6390 IC drives one half-bridge of the 3-phase power stage. The three gate drivers

are driven by the controller and the sensing signals coming from the power stage are

managed directly by the L6390 analog blocks (comparators and op-amps) which provide the

proper feedback signals to the ADC and the system controller. Each half-bridge comprises

two power switches such as IGBTs (or MOSFETs), one high side and one low side. When

the high side switch is ON, it brings the output voltage of the half-bridge to the HV bus

voltage, which can be a high DC voltage power supply with large power availability, while the

low side switch shorts the output to power ground voltage when it is ON. Thanks to the

internal floating structure for the high side switch driving, n-type IGBTs (or N-channel

MOSFETs) can be used. The gate drivers work exactly as digital/analog-power interface

between the controller and the power stage. A shunt resistor can be placed between each

low side switch and the power ground, to sense the current on each low side. The

information contained in each current sense signal can be conditioned by the L6390 op-amp

as described in Section 6.

In Figure 19 a more detailed schematic of a 3-phase power stage topology is shown. Note

that usually is recommended (not mandatory) to have some gate resistances between each

power switch gate and the correspondent gate driver output, in order to limit the current

during the gate charge. Then some filtering and/or level shifting RC networks should be

added between the shunt resistors and the correspondent comparator and op-amp input

pins of each gate driver. A unique RC network can be used for the SD pin even if it is

strongly recommended to split the capacitor in three equal components in parallel in order to

3-phase

MOTOR

HV BUS

3-phase

MOTOR

CONTROLLER

ADC

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