FAN7888 Ver la hoja de datos (PDF) - Fairchild Semiconductor

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FAN7888

3 Half-Bridge Gate-Drive IC

Fairchild Semiconductor 

Application Information

1. Protection Function

1.1 Under-Voltage Lockout (UVLO)

The high- and low-side drivers include under-voltage

lockout (UVLO) protection circuitry for each channel that

monitors the supply voltage (VDD) and bootstrap capaci-

tor voltage (VBS1,2,3) independently. It can be designed

prevent malfunction when VDD and VBS1,2,3 are lower

than the specified threshold voltage. The UVLO hystere-

sis prevent chattering during power supply transitions.

1.2 Shoot-Through Prevention Function

The FAN7888 has shoot-through prevention circuitry

monitoring the high- and low-side control inputs. It can

be designed to prevent outputs of high and low side from

turning on at same time, as shown Figure 27 and 28.

2. Operational Notes

The FAN7888 is a three half-bridge gate driver with

internal typically 120ns dead-time for the three-phase

Brushless DC (BLDC) motor drive system, as shown in

Figure 1.

Figure 29 shows a switching sequence of 120° electrical

commutation for a three-phase BLDC motor drive system.

The waveforms are idealized: they assumed that the

generated back EMF waveforms are trapezoidal with flat

tops of sufficient width to produce constant torque when

the line currents are perfectly rectangular 120° electrical

degrees with the switching sequence as shown in Figure

29. The operating waveforms of the wey-connection

reveal that repeat every 60 electrical degrees, with each

60° segment being “commutated” to another phase, as

shown in Figure 29.

HIN1,2,3/LIN1,2,3

LIN1,2,3/HIN1,2,3

HO1,2,3/LO1,2,3

Shoot-Through Prevent

After DT

LO1,2,3/HO1,2,3

After DT

FAN7888 Rev.00

Figure 27. Waveforms for Shoot-Through Prevention

HIN1,2,3/LIN1,2,3

LIN1,2,3/HIN1,2,3

HO1,2,3/LO1,2,3

Shoot-Through Prevent

After DT

LO1,2,3/HO1,2,3

FAN7888 Rev.00

Figure 28. Waveforms for Shoot-Through Prevention

© 2008 Fairchild Semiconductor Corporation

FAN7888 • Rev.1.0.0

11

www.fairchildsemi.com

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