IRS2608DSPBF データシートの表示（PDF） - International Rectifier

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IRS2608DSPBF

HALF-BRIDGE DRIVER

International Rectifier 

IRS2608DSPbF

Integrated Bootstrap Functionality

The IRS2608D embeds an integrated bootstrap FET that allows an alternative drive of the bootstrap supply for a wide

range of applications.

A bootstrap FET is connected between the floating supply VB and VCC (see Fig. 8).

Vcc

BootFet

Vb

Figure 8: Semplified BootFET connection

The bootstrap FET is suitable for most PWM modulation schemes, including trapezoidal control, and can be used

either in parallel with the external bootstrap network (diode+ resistor) or as a replacement of it. The use of the

integrated bootstrap as a replacement of the external bootstrap network may have some limitations in the following

situations:

• When the motor runs at a very low current (so that the negative phase voltage decay can be longer than

20us) and complementary PWM is not used.

• At a very high PWM duty cycle due to the bootstrap FET equivalent resistance (RBS, see page 3).

The summary for the bootstrap state follows:

• Bootstrap turns-off (immediately) or stays off when at least one of the following conditions are met:

1- HO goes/is high

2- VB goes/is high (> 1.1*VCC)

• Bootstrap turns-on when:

1- LO is high (low side is on) AND VB is low (< 1.1(VCC))

2- LO and HO are low after a LIN transition from H to L (HB output is in tri-state) AND VB goes low

(<1.1*VCC) before a fixed time of 20us.

3- LO and HO are low after a HIN transition from H to L (HB output is in tri-state) AND VB goes low

(<1.1(VCC)) before a retriggerable time of 20us. In this case the time counter is kept in reset state until

VB goes high (>1.1VCC). Please refer to the BootFET timing diagram for more details.

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