ISL6209 Datasheet, PDF (8/10 Pages) Intersil Corporation – High Voltage Synchronous Rectified Buck MOSFET Driver

ISL6209
Power Dissipation
Package power dissipation is mainly a function of the
switching frequency and total gate charge of the selected
MOSFETs. Calculating the power dissipation in the driver for
a desired application is critical to ensuring safe operation.
Exceeding the maximum allowable power dissipation level
will push the IC beyond the maximum recommended
operating junction temperature of 125°C. The maximum
allowable IC power dissipation for the SO-8 package is
approximately 800mW. When designing the driver into an
application, it is recommended that the following calculation
be performed to ensure safe operation at the desired
frequency for the selected MOSFETs. The power dissipated
by the driver is approximated as:
P = f_sw(1.5V_UQ_U + V_LQ_L) + I_VCCV_CC
where f_sw is the switching frequency of the PWM signal. V_U
and V_L represent the upper and lower gate rail voltage. Q_U
and Q_L is the upper and lower gate charge determined by
MOSFET selection and any external capacitance added to
the gate pins. The I_VCC V_CC product is the quiescent power
of the driver and is typically negligible.
1000
900
Q_U =100nC
800
Q_L= 200nC
700
Q_U = 50nC
Q_L = 100nC
Q_U = 50nC
Q_L = 50nC
600
Q_U= 20nC
500
Q_L = 50nC
400
300
200
100
0
0 200 400 600 800 1000 1200 1400 1600 1800 2000
FREQUENCY (kHz)
FIGURE 7. POWER DISSIPATION vs FREQUENCY
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