Analysis Power Dissipation Application with High Power When opera

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Analysis Power Dissipation Application with High Power When opera

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Analysis Power Dissipation Application with High Power
When operating, on-chip devices dissipate power heat way. Heat flow from higher lower temperature region. regulator, most dissipated power comes from power pass transistor Therefore, current passes through power transistor voltage across transistor, which determine amount heat generated. quantity that resists impedes this flow heat energy called thermal resistance.
Thermal topology LDO:
shown figure thermal resistance resistance from package heat dissipation reciprocal thermal conductivity package. source heat chip package. materials heat flow path between outside environment have thermal resistance temperature chip rises above ambient environment. Therefore, thermal conductivity silicon chip, molding compound, copper leadframe, thickness thermal conductivity
Introduction:
paper provides user know thermal dissipation regulators, select heat sink prevent thermal problem from exceeding maximum allowable junction temperature. regulators, thermal resistance data different packages compliant with different applications user' requirements, well determine thermal limits different packages spec. Thermal resistance, such RJC, applied determine thermal dissipation performance regulator. thermal resistance
adhesion material affect rate which heat dissipated. figure1, thermal resistance neglected because most heat flows through case into surrounding air. Same electrical resistance, summing these series resistance determines value (the chip junction ambient thermal resistance).
heat sink issue thermal resistance from junction case thermal resistance from case heat sink thermal resistance from heat sink ambient thermal resistance from case ambient
represents better performance than high thermal resistance. system that lower thermal resistance either dissipate more heat given temperature difference dissipate given amount heat with smaller temperature difference.
2001
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Case
AIC1084
Package
Package
Chip
Case
Power Loss
Natural Flow
Figure1: AIC1084 Package Thermal Metrics
manufacturers
follow
junction
temperature,
Fundamental
formula
thermal
TJ(max), which 125°C. ambient temperature, usually between -20°C 80°C. TJ(max) both specified spec LDO. maximum power dissipation package depended RJC, which measure relative performance When allowing range spec, neither heat removed junction temperature maintained below 125°C.
resistance RJC:
heat flows through case, package into surrounding air. must removed sufficient rate keep temperature transistor junction regulator from damage. When heat quantity generated device equal that removed, condition steady state achieved. Therefore, most silicon
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When external heat sinks applied, decreases with remaining same.
Measurement application AIC1084
general, with board' copper foil heat sink, copper draws heat through package' output pins into copper-foil sink surface board. Figure2, show maximum allowable dissipation ambient temperature TO-220, TO-263, TO-252 different safe operating areas. Figure3, show different packages (de-rating from figure2, Table shows value thermal resistance
thermal resistance defined
where:
(max) (max) (max) (max) (max)
=maximum recommended junction temperature
=ambient temperature user environment =maximum case temperature
TO-220, TO-263, TO-252 different safe operating areas. These figures represent thick foil this material typical copper-foil geometry heatsink area TO-220, TO-263 TO-252. Please refer
=junction ambient thermal resistance
=maximum recommended power disssipation
Table1, Table2 figure maximum power limit applied TO-220, TO-263 TO-252 packages.
Table value different AIC1084 Number Copper area side side side
Thermal resistance TO-220 50°C/W 47.5°C/W 22.4°C/W TO-263 60°C/W 54.5°C/W 31.7°C/W TO-252 100°C/W 96°C/W 70.6°C/W
Absolute maximum rating
Operating junction temperature range 0~125°C
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AIC1084CT
0.0-20
AIC1084CT
Maximum Allowable PD(W)
Maximum Allowable PD(W)
700mm2
700mm2
175mm2
175mm2 700mm2
Ambient Temperature TA°C
Ambient Temperature TA°C
Fig. Max. Allowable Ambient Temperature TO-220
AIC1084CM
Fig. AIC1084CT (De-rating from Fig.
AIC1084CM Maximum Allowable PD(W)
Maximum Allowable PD(W)
460mm2
460mm2
115mm2
115mm2 460mm2
Ambient Temperature TA°C
Ambient Temperature TA°C
Fig. Allowable Ambient Temperature TO-263
AIC1084CE
Fig. AIC1084CM De-Rating from Fig.
AIC1084CE
Maximum Allowable PD(W)
240mm2
Maximum Allowable PD(W)
240mm2 60mm2 240mm2
60mm2
Ambient Temperature TA°C
Ambient Temperature TA°C
Fig. Allowable Ambient Temperature TO-252
Fig. AIC1084CE (De-Rating from Fig.
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value, maximum allowable
select calculate correct high power LDO:
Safe operating area (SOA) maintains junction temperature below maximum allowable temperature under normal operating environment. select achieve normal junction
found reading intersection =25°C with curve 115mm figure
That thermal resistance 54.5°C/W with power limit (max) 1.83W when heat sink 115mm pattern required. case, power dissipation =1.7W shall below power limit (max) when loading current
temperature LDO, users need employ following four fundamental steps. amount heat being generated power limit maximum allowable junction temperature available from data book maximum ambient temperature thermal resistance available from databook Selected correct safe operating area
Step3: Continuing above example, AIC1084CM junction temperature obtained follows:
(max) 54.5 125°C
.65°C
find that system stable terms heat when (max)<<1.83W, thermal resistance (junction ambient) RJA=54.5°C/W<< 60°C/W from table1 user safe operating area chosen suitably. addition, thermal resistance TO-263 surface-mount package 60°C/W heatsink) defined
maximum power dissipation application Selected maximum power limit
requirement
Step1: example: =5V, VOUT =3.3V, IOUT =1A, =6°C/W (TO-263), =25°C choose safe operating area =?mm IOUT (max)=?A user maximum power dissipation.
data book. need heat sink when would like decrease thermal resistance surface-mount package RJA=54.5°C/W (which less than 60°C/W said data book).
(VIN VOUT IOUT 3.3) 1.7W
1.7W user operating
Step2: Find value thermal resistance need (RJA) table1 115mm value maximum power limit max) axis figure
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Table2: view thermal test pattern AIC1084 actual scale
10.66mm
10.29mm
16.51mm
6.73mm
TO-220
TO-263
TO-252
11.06mm
8.5mm
Copper area, 1oz, 175mm
10.66mm
Copper area, 1oz, 115mm
10.29mm 11.06mm
Copper area, 1oz, 60mm
6.73mm 8.5mm
16.51mm
21.32mm
20.58mm
Copper area, 1oz, 700mm
13.46mm
Copper area, 1oz, 460mm
Copper area, 1oz, 240mm
33.02mm
22.12mm
17.5mm
Conclusion
Until now, heat problem high power perplexing choose appropriates heatsink (PCB) device lower thermal resistance. Even, price another consideration user employ application LDO. According above calculation thermal resistance junction temperature, have found that thermal resistance affects dissipative heat system. important factor that thermal resistance influence rate heat dissipation when maximum input voltage, maximum load current, highest ambient operating temperature,and nominal output voltage, based spec, applied. addtion, also must follow maximum power dissipation (power limit) maximum junction ambient thermal resistance requirements. selected pakage can' meet requirement thermal resistance limits, will need heat sink keep junction temperaure below 125°C. Therefore, high power series products with kinds power dissipation, essential choose enough area heatsink. Besides, thermal shutdown, protective
function, triggered when abnormally operated high environment power dissipation, which limits spec. Thermal shutdown, temperature between 165°C, from equips system protect from damage.
Reference:
AIC1084 dropout positive adjustable regulator from analog integrated corp.

Analysis Power Dissipation Application with High Power When opera

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