EVM7765AXF datasheet(9/24 Pages) SEMTECH

9 / 24 page

TEST AND MEASUREMENT PRODUCTS

2006 Semtech Corp. , Rev. 11, 7/18/06

www.semtech.com

E7765

Application Information (continued)

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 cal-

culate 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 Rθ.

Rθ(heatsink_system) = (TJmax - Tambient - P * θJC) / P

where, Rθ (heatsink_system) is the thermal resistance

of the entire heatsink system

TJmax is the maximum die temperature

(100°C)

Tambient is the maximum ambient air temp

expected at the heatsink (°C)

P is the maximum expected power

dissipation of the E7765 (Watts)

θJC is the thermal impedance of the

E7765 junction to case (0.8°C/W)

The graph below uses the power estimates from the previ-

ous graph and indicates the required maximum thermal

impedances required for the heatsinking system using the

above formula with Tambient at 35°C.

Care needs t

Care needs to be tak

o be tak

o be taken when increasing the operating

en when increasing the operating

DBIAS, RAD

DBIAS, RADJ, F

J, F

J, FAD

ADJ in

J in

J inputs. Monit

puts. Monit

puts. Monitoring the die t

oring the die t

oring the die tem

empera-

pera-

ture t

ture to insure adeq

o insure adeq

o insure adequat

uat

uate heatsinking and air

e heatsinking and air

e heatsinking and airflo

flo

flow is v

w is v

w is ver

eryyyyy

impor

por

portant.

tant.

The power consumption goes up as the power supplies

are raised in voltage, and the RADJ, FADJ and DBIAS set-

tings are increased for higher frequency performance.

There are specifications and graphs for the relationships

of these controls to overall performance in the DC Specifi-

cations section. Refer to them for choosing the settings

for a particular system performance. This section deals

with how to heatsink the various power dissipation levels.

Cooling Considerations

Depending on the applied power supply levels and bias

conditions the E7765 will use, various methods of

heatsinking will be required to keep the maximum die junc-

tion termperature within a safe range and below the speci-

fied maximum of 100°C.

The E7765 package has an integral heat slug 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

θJC (junction-to-case) and is

specified at 0.8°C/Watt.

In order to calculate what type of heatsinking should be

applied to the E7765, the designer needs to determine

the worst case power dissipation of the device in the appli-

cation. The graph above gives a good visual relationship of

the range of power dissipation that can be expected from

the E7765. The range of power covers the different modes

of operation, power supply settings, and performance bias

adjustments available. Use the data and graphs in subse-

quent sections to determine a particular applications power

dissipation.

Another variable that needs to be determined is the maxi-

mum ambient air temperature that will be surrounding or

blowing on the device and/or the heatsink system in the

application (assuming an air cooled system). A heatsinking

solution should be chosen to be at or below a certain ther-

mal impedance known as Rθ in units of °C/Watt. The

heatsinking system is a combination of factors including

the actual heatsink chosen and the selection of the inter-

face material between the E7765 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

More information on heatsink system selections can be

read on heatsink vendors’ web sites and in the Semtech

Application Note #ATE-A2 Cooling High Power, High Den-

sity Pin Electronics.

Required Heatsinking Thermal Resistances

Covers Complete Range of Supplies (All PON=1)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Min Supplies

Typ Supplies

Max Supplies

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