BU7251G Datasheet, PDF (15/19 Pages) Rohm – Comparators: Low Voltage CMOS

BU7251G,BU7251SG, BU7231G,BU7231SG,
BU7252F/FVM,BU7252S F/FVM,BU7232F/FVM,BU7232S F/FVM
Technical Note
●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.
P_Lo_Sw_Iのer_消di_費ss_電ipa_力tio_[Wn P_] d:[W]
θja = ( Tj _ーTa ) / Pd [_℃/W]
Pd(max)
P2
θja2 < θja1
Ambient temperature Ta [℃]
P1
θja2
Tj(max)
θja1
Chip surface temperature Tj [℃]
0
25
50
75
100
125
150
Power dissipation P [W]
(a) Thermal resistance
Ambie_周nt_囲te_温mp_度er_Ta_atu_[℃re_]:Ta[℃]
BU7251/BU7231
T j(max)
(b) Derating curve
Fig. 93. Thermal resistance and power dissipation
800
1000
600
540[mw] ^BU7251G(*8)
BU7231G(*8)
400
200
800
620[mw]
BU7252F(*9)
BU7232F(*9)
600
480[mw]
BU7252FVM(*10)
BU7232FVM(*10)
400
200
0
0
50
85 100
150
AMBIENT TEMPERATURE [℃]
(c) BU7251G BU7231G
800
0
0
50
85 100
150
AMBIENT TEMPERATURE [℃]
(d) BU7252F/FVM BU7232F/FVM
1000
600
540[mw] ^BU7251SG(*8)
800
620[mw]
BU7252SF(*9)
BU7232SF(*9)
BU7231SG(*8)
600
480[mw]
BU7252SFVM(*10)
BU7232SFVM(*10)
400
400
200
200
0
0
50
100 ¹⁰⁵
150
AMBIENT TEMPERATURE [℃]
(e) BU7251SG BU7231SG
0
0
50
100¹⁰⁵
150
AMBIENT TEMPERATURE [℃]
(f) BU7252S F/FVM BU72432S F/FVM
(*8)
(*9)
(*10)
5.4
6.2
4.8
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.
Derating curve
Unit
[mW/℃]
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