Technical Note
BU7251G,BU7251SG, BU7231G,BU7231SG,
BU7252F/FVM,BU7252S F/FVM,BU7232F/FVM,BU7232S F/FVM
15/18
●Derating curve
Power dissipation (total loss) indicates the power that can be consumed by IC at Ta=25℃(normal temperature).IC is heated
when it consumed power, and the temperature of IC ship becomes higher than ambient temperature. The temperature that
can be accepted by IC chip depends on circuit configuration, manufacturing process, and consumable power is limited. Power
dissipation is determined by the temperature allowed in IC chip (maximum junction temperature) and thermal resistance of
package (heat dissipation capability). The maximum junction temperature is typically equal to the maximum value in the
storage package (heat dissipation capability). The maximum junction temperature is typically equal to the maximum value in
the storage temperature range. Heat generated by consumed power of IC radiates from the mold resin or lead frame of the
package. The parameter which indicates this heat dissipation capability (hardness of heat release) is called thermal
resistance, represented by the symbol
θj-a[℃/W]. The temperature of IC inside the package can be estimated by this thermal
resistance. Fig.93 (a) shows the model of thermal resistance of the package. Thermal resistance
θja, ambient temperature Ta,
junction temperature Tj, and power dissipation Pd can be calculated by the equation below :
θja = (Tj-Ta) / Pd
[℃/W]
····· (Ⅰ)
Derating curve in Fig.93 (b) indicates power that can be consumed by IC with reference to ambient temperature. Power that
can be consumed by IC begins to attenuate at certain ambient temperature. This gradient is determined by thermal
resistance
θja. Thermal resistance θja depends on chip size, power consumption, package, ambient temperature, package
condition, wind velocity, etc even when the same of package is used. Thermal reduction curve indicates a reference value
measured at a specified condition. Fig94(c)-(f) show a derating curve for an example of BU7251family, BU7252 family, BU7231
family, BU7232 family.
(*8)
(*9)
(*10)
Unit
5.4
6.2
4.8
[mW/℃]
When using the unit above Ta=25[℃], subtract the value above per degree[℃]. Permissible dissipation is the value
when FR4 glass epoxy board 70[mm]×70[mm]×1.6[mm] (cooper foil area below 3[%]) is mounted.
Fig. 94.
050
75
100
125
150
25
P1
P2
Pd(max)
LSI
の消費(fèi)電力[W]
θja2
θja1
Tj(max)
θja2 < θja1
周?chē)鞙囟萒a[℃]
BU7251/BU7231
Tj(max)
Power dissipation Pd:[W]
Ambient temperature:Ta[
℃]
(a) Thermal resistance
(b) Derating curve
Fig. 93. Thermal resistance and power dissipation
Derating curve
0
200
400
600
800
050
100
150
AMBIENT TEMPERATURE [
℃]
PO
W
ER
D
ISSI
PAT
IO
N
[
m
W
]
.
85
0
200
400
600
800
1000
0
50
100
150
AMBIENT TEMPERATURE [
℃]
PO
W
ER
D
ISSI
PA
T
IO
N
[m
W
]
.
85
0
200
400
600
800
0
50
100
150
AMBIENT TEMPERATURE [
℃]
PO
W
ER
D
ISSI
PAT
IO
N
[
m
W
]
.
BU7231SG(*8)
105
0
200
400
600
800
1000
0
50
100
150
AMBIENT TEMPERATURE [
℃]
PO
W
ER
D
ISSI
PA
T
IO
N
[m
W
]
.
105
(c) BU7251G
BU7231G
(d) BU7252F/FVM
BU7232F/FVM
(e) BU7251SG
BU7231SG
(f) BU7252S F/FVM
BU72432S F/FVM
BU7251SG(*8)
BU7251G(*8)
BU7231G(*8)
540[mw]
620[mw]
480[mw]
540[mw]
BU7252F(*9)
BU7232F(*9)
BU7252FVM(*10)
BU7232FVM(*10)
620[mw]
480[mw]
BU7252SF(*9)
BU7232SF(*9)
BU7252SFVM(*10)
BU7232SFVM(*10)
Ambient temperature Ta [
℃]
Chip surface temperature Tj [
℃]
Power dissipation P [W]
θja = ( Tj ーTa ) / Pd [℃/W]