MCP1824ST-3302E Datasheet, PDF (22/34 Pages) Microchip Technology – 300 mA, Low Voltage, Low Quiescent Current LDO Regulator

MCP1824/MCP1824S
The maximum power dissipation capability for a
package can be calculated given the junction-to-
ambient thermal resistance and the maximum ambient
temperature for the application. Equation 5-4 can be
used to determine the package maximum internal
power dissipation.
EQUATION 5-4:
P_D(MAX)
=
(_---T_{----J--(--M----A---X----)---–----}T_{----A---(--M----A---X---)---})
Rθ_JA
P_D(MAX) = Maximum device power dissipation
T_J(MAX) = maximum continuous junction
temperature
T_A(MAX) = maximum ambient temperature
Rθ_JA = Thermal resistance from junction-to-
ambient
EQUATION 5-5:
T_J(RISE) = P_D(MAX) × Rθ_JA
T_J(RISE) = Rise in device junction temperature
over the ambient temperature
P_D(MAX) = Maximum device power dissipation
Rθ_JA = Thermal resistance from junction-to-
ambient
EQUATION 5-6:
T_J = T_J(RISE) + T_A
T_J = Junction temperature
T_J(RISE) = Rise in device junction temperature
over the ambient temperature
T_A = Ambient temperature
5.3 Typical Application
Internal power dissipation, junction temperature rise,
junction temperature, and maximum power dissipation
is calculated in the following example. The power
dissipation as a result of ground current is small
enough to be neglected.
5.3.1 POWER DISSIPATION EXAMPLE
Package
Package Type = SOT-223-5
Input Voltage
V_IN = 3.3V ± 5%
LDO Output Voltage and Current
V_OUT = 2.5V
I_OUT = 300 mA
Maximum Ambient Temperature
T_A(MAX) = 60°C
Internal Power Dissipation
P_LDO(MAX) = (V_IN(MAX) – V_OUT(MIN)) x I_OUT(MAX)
P_LDO = ((3.3V x 1.05) – (2.5V x 0.975))
x 300 mA
P_LDO = 0.308 Watts
5.3.1.1 Device Junction Temperature Rise
The internal junction temperature rise is a function of
internal power dissipation and the thermal resistance
from junction-to-ambient for the application. The
thermal resistance from junction-to-ambient (Rθ_JA) is
derived from EIA/JEDEC standards for measuring
thermal resistance. The EIA/JEDEC specification is
JESD51. The standard describes the test method and
board specifications for measuring the thermal
resistance from junction to ambient. The actual thermal
resistance for a particular application can vary
depending on many factors such as copper area and
thickness. Refer to AN792, “A Method to Determine
How Much Power a SOT23 Can Dissipate in an
Application” (DS00792), for more information regarding
this subject.
T_J(RISE) = P_TOTAL x Rθ_JA
T_JRISE = 0.308 W x 62° C/W
T_JRISE = 19.1°C
DS22070A-page 22
© 2007 Microchip Technology Inc.