E7804BHF Semtech, E7804BHF Datasheet - Page 24

• Manufacturer Part Number: E7804BHF
• Manufacturer: Semtech

Specifications of E7804BHF

• Operating Temperature (max): 100C
• Package Type: MQFP
• Mounting: Surface Mount
• Lead Free Status / Rohs Status: Not Compliant

Computing Maximum Power Consumption
The diagram below shows the power consumption of the
Edge7804 as a function of clocking frequency of all
channels.
The power consumption goes up with frequency and output
voltage swing.
Cooling Considerations
Depending on the maximum operating frequencies and
voltage swings the Edge7804 will need to drive, it may
require the use of heatsinking to keep the maximum die
junction termperature within a safe range and below the
specified maximum of 100˚C.
The Edge7804 package has an internal heatspreader
located at the top side of the package to efficiently conduct
heat away from the die to the package top. The thermal
resistance of the package to the top is the
to-case) and is specified at 4˚C/Watt.
In order to calculate what type of heatsinking should be
applied to the Edge7804, the designer needs to determine
the worst case power dissipation of the device in the
application. The graph above gives a good visual
relationship of the power dissipation to the maximum
operating frequency (all channels simultaneously) and
driver output voltage swings. Another variable that needs
to be determined is the maximum ambient air temperature
that will be surrounding or blowing on the device and/or
the heatsink system in the application (assuming an air
Application Information (continued)
TEST AND MEASUREMENT PRODUCTS
2005 Semtech Corp. / Rev. 5, 12/6/05
JC
(junction-
24
cooled system). A heatsinking solution should be chosen
to be at or below a certain thermal impedance known as
R in units of ˚C/Watt. The heatsinking system is a
combination of factors including the actual heatsink chosen
and the selection of the intertface material between the
Edge7804 and the heatsink itself. This could be thermal
grease or thermal epoxy, and they also have their own
thermal impedances. The heatsinking solution will also
depend on the volume of air passing over the heatsink
and at what angle the air is impacting the heatsink. There
are many options available in selecting a heatsinking
system. The formula below shows how to calculate the
required maximum thermal impedance for the entire
heatsink system. Once this is known, the designer can
evaluate the options that best fit the system design and
meet the required R .
R (heatsink_system) = (T
The graph below uses the power estimates from the
previous graph and indicates the required maximum
thermal impedances required for the heatsinking system
using the above formula with T
where, R (heatsink_system) is the thermal
T
T
P is the maximum expected power
Jmax
ambient
JC
resistance of the entire heatsink system
(100˚C)
expected at the heatsink (˚C)
dissipation of the Edge7804 (Watts)
Edge7804 junction to case (4˚C/W)
is the thermal impedance of the
is the maximum die temperature
is the maximum ambient air temp
Jmax
ambient
- T
ambient
Edge7804
PRELIMINARY
at 35˚C.
www.semtech.com
- P *
JC
) / P