11
Thermal Management
Assuming that there is no forced air flow, the
package termperature rise above ambient (
∆T) may
be calculated using the following expression:
∆T
≈ 80 A -0.7 p 0.85 ( °C)
where A = the effective surface area in square
inches (including heat sink if used;) P = power
dissipation in watts.
The total surface area of the AHF package is 4.9
square inches. If a worse case full load efficiency of
78% is assumed, then the case temperature rise
can be calculated as follows:
P = P
OUT [
1
- 1
] = 12 [ 1 - 1] = 3.4 W
∆T = 80 (4.9)-0.7 (3.4)0.85 = 74°C
Hence, if T
AMBIENT = +25°C, the DC/DC converter
case temperature will be approximately 100°C if no
heat sink or air flow is provided.
To calculate the heat sink area required to maintain
a specific case temperature rise, the above equa-
tion may be manipulated as follows:
A
HEAT SINK = [
∆T
] -1.43 - A
PKG
80P 0.85
As an example, if a maximum case temperature
rise of 50°C above ambient is desired, then the
required effective heat sink area is:
A
HEAT SINK = [ 50
] -1.43 -4.9 = 3.75 in.2
80 (3.4) 0.85
E
FF
.78
STANDARDIZED MILITARY DRAWING
CROSS REFERENCE
Model
Drawing Number
AHF2805S/CH
SMD #5962-91600
AHF2812S/CH
SMD #5962-94568
AHF2815S/CH
SMD #5962-94563
AHF2812D/CH
SMD #5962-92111
AHF2815D/CH
SMD #5962-92351
PART NUMBER
AHF 28 xx x F/ x
Model
Input Voltage
Output Voltage
05— 5V DC
12—12V DC
15—15V DC
S—Single
D—Dual
Available Screening Levels and Process Variations for AHF Series
Screening (see table)
Omit for -20°C to +85°C
ES -55°C to +125°C
HB— -55°C to +125°C
CH— Class H complaint
See table for standard
Mlitary drawing number
Package Option
Omit For Standard
F-Flange
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