ISL55110 Datasheet, PDF (13/15 Pages) Intersil Corporation – Dual, High Speed MOSFET Driver

ISL55110, ISL55111
channel power consumption, only include this current
once.
2. 10pF is the approximate parasitic Capacitor (Inverters,
etc.), which the V_DD drives
3. 135pF is the approximate parasitic at the D_OUT and its
Buffers. This includes the effect of the Crow-bar Current.
4. C_L is the Load capacitor being driven
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 12, 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 1 or 2 under Thermal Information, given
the high speed pulse rate and amplitude capability of the
ISL55110, 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--}
θ_JA
(EQ. 2)
where:
• T_JMAX = Maximum junction temperature
• T_AMAX = Maximum ambient temperature
• θ_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 heat sink/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
θ_JA ratings of the TSSOP and QFN package 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, ISL55111 QFN package
metal plane is used for heat sinking of the device. It is
electrically connected to the negative supply potential
ground.
Power Supply Sequencing
The ISL55110, ISL55111 references both V_DD and the V_H
driver supplies with respect to Ground. Therefore, apply
V_DD, then V_H. Digital Inputs should never be open. Do not
apply slow analog ramps to the inputs. Again, place
decoupling 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 or to request a device characterization to your
requirements in our lab.
13
FN6228.3
December 16, 2008