33883 datasheet(13/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33883

FUNCTIONAL DEVICE OPERATION

OPERATIONAL MODES

TURN-ON

For turn-on, the current required to charge the gate source

capacitor Ciss in the specified time can be calculated as

follows:

IP = Qg/tr = 80 nC/80 ns ≈ 1.0 A

Where Qg is power MOSFET gate charge and tr is peak

current for rise time.

TURN-OFF

The peak current for turn-off can be obtained in the same

way as for turn-on, with the exception that peak current for fall

time, tf, is substituted for tr:

IP = Qg/tf = 80 nC/80 ns ≈ 1.0 A

In addition to the dynamic current required to turn off or on

the MOSFET, various application-related switching scenarios

must be considered. These scenarios are presented in

Figure 7. In order to withstand high dV/dt spikes, a low

resistive path between gate and source is implemented

during the OFF-state.

Figure 7. OFF-State Driver Requirement

Driver Requirement:

Low Resistive Gate-

Source Path During

OFF-State

Flyback spike charges low-

side gate via Crss charge

current Irss up to 2.0 A.

Causes increased uncon-

trolled turn-on of low-side

MOSFET.

Ciss

Crss

VBAT

Driver Requirement:

Low Resistive Gate-

Source Path During

OFF-State. High Peak

Sink Current Capability

Flyback spike pulls down

high-side source VGS.

Delays turn-off of high-

side MOSFET.

Ciss

Crss

VBAT

Driver Requirement:

High Peak Sink Current

Capability

Flyback spike charges low-

side gate via Crss charge

current Irss up to 2.0 A.

Delays turn-off of low-side

MOSFET.

Ciss

Crss

VBAT

Driver Requirement:

Low Resistive Gate-

Source Path During

OFF-State

Ciss

Crss

VBAT

Flyback spike pulls down

high-side source VGS.

Causes increased uncon-

trolled turn-on of high-side

OFF

GATE_LS

ILOAD

Irss

VGATE

-VDRN

GATE_HS

GATE_LS

GATE_HS

GATE_LS

GATE_HS

GATE_LS

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