CS9202 Datasheet, PDF (5/6 Pages) ON Semiconductor – Micropower 3.3 V, 100 mA Linear Regulator with NOCAP

CS9202
CALCULATING POWER DISSIPATION IN A
SINGLE OUTPUT LINEAR REGULATOR
The maximum power dissipation for a single output
regulator (Figure 10) is:
PD(max) + {VIN(max) * VOUT(min)} IOUT(max)
) VIN(max)IQ
(1)
where:
V_IN(max) is the maximum input voltage,
V_OUT(min) is the minimum output voltage,
I_OUT(max) is the maximum output current for the
application, and
I_Q is the quiescent current the regulator consumes at
I_OUT(max).
Once the value of P_D(max) is known, the maximum
permissible value of R_ΘJA can be calculated:
R_QJA
+
150°C *
PD
TA
(2)
I_IN
V_IN
CS9202
I_OUT
V_OUT
I_Q
The value of R_ΘJA can then be compared with those in the
package section of the data sheet. Those packages with
R_ΘJA ’s less than the calculated value in equation 2 will keep
the die temperature below 150°C.
In some cases, none of the packages will be sufficient to
dissipate the heat generated by the IC, and an external
heatsink will be required.
HEAT SINKS
A heat sink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
into the surrounding air.
Each material in the heat flow path between the IC and the
outside environment will have a thermal resistance. Like
series electrical resistances, these resistances are summed to
determine the value of R_ΘJA:
R_QJA + R_QJC ) R_QCS ) R_QSA
(3)
where:
R_ΘJC = the junction−to−case thermal resistance,
R_ΘCS = the case−to−heatsink thermal resistance, and
R_ΘSA = the heatsink−to−ambient thermal resistance.
R_ΘJC appears in the package section of the data sheet.
Like R_ΘJA, it too is a function of package type. R_ΘCS and
R_ΘSA are functions of the package type, heatsink and the
interface between them. These values appear in heat sink
data sheets of heat sink manufacturers.
Figure 10. Single output regulator with key
performance parameters labeled.
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