Dc/Dc c
onVerters
The HR700 Series of DC/DC converters has an upper operating
temperature of + 85°C at the baseplate of the case. The degree of
heat sinking required to remain within this limit may be determined
from Figure 1 which shows the maximum allowed internal power dissi-
pation (P
DISS
vs. ambient temperature for various heat sink thermal
resistances. P
DISS
may be calculated as:
P
DISS
= P
OUT
/ efficiency – P
OUT
The efficiency for all combinations of POUT and VIN for the various
models may be obtained from the graphs on the preceding pages.
Example: onverter = HR702-2815, T
AmB
= 70°C,
C
V
IN
= 28 VDC, P
OUT
= 45 watts
Efficiency = 85% (From Figure 7)
P
DISS
= (45 / 85) – 45 = 7.95 watts
From Figure 1 we can see that this situation will require thermal resis-
tance of approximately 4.5°C / watt.
Conversely we may also find the maximum ambient temperature
which can be tolerated if we know the heat sink thermal resistance.
Example: onverter = HR701-2805, VIN = 28 VDC, P
OUT
= 45 W.
C
Thermal Resistance = 3°C / watt.
Efficiency = 83.5% (From Figure 3)
P
DISS
= (45 / 0.835) – 45 = 8.89 watts.
tHermaL management
c
alculating
m
aXimum
a
mbient
t
emperature
HR700
SERIES
70 WATT
From Figure 1 we can see that the maximum allowed am ient temper-
b
ature is ap rox mately 75°C.
p i
An mFW Series converter in still air (other than convective currents)
and with no conductive cooling paths other than through electrical
connections at the pins will exhibit a thermal resistance of approxi-
mately 4°C / watt. In cases where this value proves to be too high it is
recommended that additional heat sinking be supplied. The simplest
method of accomplishing this is to firmly attach the converter to a PCB
thereby providing a conductive thermal path. Secondly it is recom-
mended that airflow be provided over the converter. Although each
situation requires a thorough thermal analysis these two measures
can reduce the thermal resistance to as low as 2°C / watt. If calcula-
tions indicate further heat sinking is required it is recommended that
additional thermal mass be provided either under the base plate or on
top of the converter’s mounting flanges or both.
h
eat
s
ink
r
ecommenDations
pin Out
20
W
/W C/W
°
C/W
°
C/
4
°
CU=3
°
U=2 U=0
U=
15
10
5
pin dual Output
1
P
ositive Input
2
C
ase Ground
3
I
nput Common
4
I
nhibit/Sync In
5
N
egative Output
6
P
ositive Output
7, 8 utput Common
O
9, 10 o Connection
N
triple Output
Positive Input
Case Ground
Input Common
Inhibit/Sync In
Neg. Aux. Output
Positive Aux. Output
Output Common
main (+5) Output
Watts
Squared corner indicates pin one.
20° 40° 60° 80° 100° 120° 140°
Degrees Centigrade
Internal Power Dissipation (max)
vs. Ambient Temperature
F
IGuRE
1
1
2
3
4
BOTTOM VIEW
MFW
See case L for dimensions.
9
7
5
10
8
6
F
IGuRE
2: P
IN
O
uT
www.interpoint.com
Page 4 of 7
HR700 Rev C - 20100212
INTERPOINT [ INTERPOINT CORPORATION COMPANY ]
