33883 Datasheet, PDF (13/21 Pages) Freescale Semiconductor, Inc – H-Bridge Gate Driver IC

OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
TURN-ON
For turn-on, the current required to charge the gate source
capacitor C_iss in the specified time can be calculated as
follows:
I _P = Q _g / t _r = 80 nC / 80 ns ≈ 1.0 A
Where Q_g is power MOSFET gate charge and t_r 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, t_f, is substituted for t_r:
I_P = Q_g/t_f = 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.
Flyback spike charges low-
side gate via C_rss charge
current I_rss up to 2.0 A.
Causes increased uncon-
trolled turn-on of low-side
MOSFET.
Flyback spike pulls down
high-side source V_GS.
Delays turn-off of high-
side MOSFET.
Flyback spike charges low-
side gate via C_rss charge
current I_rss up to 2.0 A.
Delays turn-off of low-side
MOSFET.
Flyback spike pulls down
high-side source V_GS.
Causes increased uncon-
trolled turn-on of high-side
C_rss
GATE_HS
V_GATE
C_iss
I_rss ^Crss
GATE_LS
OFF
C_iss
V_BAT
C_rss
GATE_HS
L1 ^ILOAD _Ciss
C_rss
GATE_LS
OFF
C_iss
V_BAT
C_rss
OFF
GATE_HS
L1 ^ILOAD
C_iss
C_rss
GATE_LS
C_iss
V_BAT
C_rss
OFF
V_GATE
-V_{DRN GATE_HS}
L1 ^ILOAD
C_iss
C_rss
V_BAT
L1 ^ILOAD
GATE_LS
C_iss
Driver Requirement:
Low Resistive Gate-
Source Path During
OFF-State
Driver Requirement:
Low Resistive Gate-
Source Path During
OFF-State. High Peak
Sink Current Capability
Driver Requirement:
High Peak Sink Current
Capability
Figure 7. OFF-State Driver Requirement
Driver Requirement:
Low Resistive Gate-
Source Path During
OFF-State
Analog Integrated Circuit Device Data
Freescale Semiconductor
33883
13