AN2388 datasheet(29/54 Pages) STMICROELECTRONICS

29 / 54 page

AN2388

Hardware design

29/54

The cell made of Q1-C5-R4 is used to separate the issues of cancelling of the switching

cross-conduction and control of the winding dV/dt regardless of the operating conditions and

IGBT junction temperature. In particular, the cell provides a low impedance path to the Miller

current when the adjacent power switch turns on, canceling any cross-conduction current.

So the half-bridge turn-on switching dV/dt is only defined by the gate drive resistor value

(R2, R6, R13, R18, R27 & R32). The comparator integrated in the L6386 (IC2) is used to

provide an over-current protection. If the voltage applied on pin 6 reaches 0.5V typical, the

Diag output (pin 5) is pulled down as well as the shut-down input (pin 2). Then the three half-

bridges are shut-down. In regulator operation this protection never triggers as the micro-

controller limits the motor current to the pre-set values.

The same circuit has also been implemented to provide over-temperature protection. This is

done via the IC3 comparator input. An OR function is made paralleling the diagnostic output

of IC2 and IC3. A third protection can be implemented using the IC1 input comparator, for

example a high side over-current protection with the PowerBD-1000 or the PowerBD-3000.

3.5

Current sensing board

The current sensing board has been designed to sense the line currents. Only two phase

current in this application are detected. The full schematic is shown in Figure 26.

Figure 26.

Current sensing board schematic

The working principle of the above circuitry is very simple: two Hall effect (LTSR 6NP)

current sensors measure the phase currents ia, ib producing an output voltage proportional

to the related current. This voltage is then amplified (see Figure 27) in order to obtain a rail

to rail voltage in steady state condition. An external voltage reference has been used. This is

necessary to force into the current sensor the same offset value. Although the sensor has

got an embedded voltage reference, this is not as stable as the external one. The voltage

signals proportional to the three-phase current are then passed to the Gate Driver Board

through a shielded flat cable.

/TL431

10K

R1 100K

R4 100K

TS824AILT-2.1

R13

R10 15K

10K

CON5A

C1TBD

C5 TBD

C14

100nF

C12

100nF

3.3uF

100nF

CON2

U1A

TS272

U1B

TS272

R12

R110

CS1

LEM LTSR6-NP/LTS6-NP

+5V

out

Ref

out

+5V

3.3uF

CON2

C13

330uF

100nF

CS2

LEM LTSR6-NP/LTS6-NP

+5V

out

Ref

out

+5V

100nF

Current_sense_phaseB

V_ref

Current_sense_phaseA

+5_V

Current_sense_phaseA

Current_sense_phaseB

V_ref

+5_V

V_ref

+5_V

V_ref

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