ISL55110IVZ-T Datasheet, PDF (14/18 Pages) Intersil Corporation – Dual, High Speed MOSFET Driver

ISL55110, ISL55111
Power Dissipation Discussion
Specifying continuous pulse rates, driver loads and driver level
amplitudes are key in determining power supply requirements,
as well as dissipation/cooling necessities. Driver output patterns
also impact these needs. The faster the pin activity, the greater
the need to supply current and remove heat.
As detailed in the “Power Dissipation Calculation” on page 13,
power dissipation of the device is calculated by taking the DC
current of the V_DD (logic) and V_H current (driver rail) times the
respective voltages and adding the product of both calculations.
The average DC current measurements of I_DD and IH should be
done while running the device with the planned V_DD and V_H
levels and driving the required pulse activity of both channels at
the desired operating frequency and driver loads.
Therefore, the user must address power dissipation relative to
the planned operating conditions. Even with a device mounted
per notes 4 or 5 under “Thermal Information”, given the high
speed pulse rate and amplitude capability of the ISL55110 and
ISL55111, it is possible to exceed the +150°C “absolute
maximum junction temperature”. Therefore, it is important to
calculate the maximum junction temperature for the application
to determine if operating conditions need to be modified for the
device to remain in the safe operating area.
The maximum power dissipation allowed in a package is
determined according to Equation 2:
P_DMAX
=
T_{----J---M-----A----X------}-_----T_{----A----M----A----X--}
_JA
(EQ. 2)
where:
• T_JMAX = Maximum junction temperature
• T_AMAX = Maximum ambient temperature
• _JA = Thermal resistance of the package
• P_DMAX = Maximum power dissipation in the package
The maximum power dissipation actually produced by an IC is
the total quiescent supply current times the total power supply
voltage, plus the power in the IC due to the loads. Power also
depends on number of channels changing state and frequency of
operation. The extent of continuous active pulse generation will
greatly effect dissipation requirements.
The user should evaluate various heatsink/cooling options in
order to control the ambient temperature part of the equation.
This is especially true if the user’s applications require
continuous, high-speed operation. A review of the _JA ratings of
the TSSOP and QFN packages clearly show the QFN package to
have better thermal characteristics.
The reader is cautioned against assuming a calculated level of
thermal performance in actual applications. A careful inspection
of conditions in your application should be conducted. Great care
must be taken to ensure die temperature does not exceed
+150°C Absolute Maximum Thermal Limits.
Important Note: The ISL55110 and ISL55111 QFN package metal
plane is used for heat sinking of the device. It is electrically
connected to ground (i.e., pin11).
Power Supply Sequencing
Apply V_DD, then V_H.
Power-Up Considerations
Digital inputs should never be undriven. Do not apply slow analog
ramps to the inputs. Again, place decoupling caps as close to the
package as possible for both V_DD and especially V_H.
Special Loading
With most applications, the user will usually have a special load
requirement. Please contact Intersil for evaluation boards.
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FN6228.7
May 30, 2014