ISL55111 Intersil Corporation, ISL55111 Datasheet - Page 13

• Manufacturer Part Number: ISL55111
• Description: (ISL55110 / ISL55111) High Speed MOSFET Driver
• Manufacturer: Intersil Corporation

Where:
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 Section,
Power Dissipation of the device is calculated by taking the
DC current of the VDD (logic) and VH Current (Driver rail)
times the respective voltages and adding the product of both
calculations. The average DC current measurements of IDD
and IH should be done while running the device with the
planned VDD and VH 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 Note 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:
where:
• T
• T
• θ
• P
P
1. 3.3mA is the quiescent Current from the VDD. This
forms a small portion of the total calculation. When figuring
two channel power consumption, only include this current
once.
2. 10pF is the approximate parasitic Capacitor
(Inverters, etc.), which the VDD drives
3. 135pF is the approximate parasitic at the DOUT and its
Buffers. This includes the effect of the Crow-bar Current.
4. CL is the Load capacitor being driven
DMAX
AMAX
JA
JMAX
DMAX
= Thermal resistance of the package
=
= Maximum junction temperature
= Maximum ambient temperature
T
-------------------------------------------- -
= Maximum power dissipation in the package
JMAX
θ
JA
- T
AMAX
13
ISL55110, ISL55111
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
Theta-j 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
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 VDD and the VH
driver supplies with respect to Ground. Therefore apply
VDD, then VH. 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 VDD
and especially VH.
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.
150°C
March 21, 2007
Absolute
FN6228.1