Datasheet

MCP1826/MCP1826S
DS22057B-page 20  2007-2013 Microchip Technology Inc.
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:
EQUATION 5-5:
EQUATION 5-6:
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
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 (R
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 Appli-
cation” (DS00792), for more information regarding this
subject.
P
DMAX
T
JMAX
T
AMAX
–
R
JA
---------------------------------------------------=
P
D(MAX)
= Maximum device power dissipation
T
J(MAX)
= Maximum continuous junction
temperature
T
A(MAX)
= Maximum ambient temperature
R
JA
= Thermal resistance from junction to
ambient
T
JRISE
P
DMAX
R
JA
=
T
J(RISE)
= Rise in device junction temperature
over the ambient temperature
P
D(MAX)
= Maximum device power dissipation
R
JA
= Thermal resistance from junction to
ambient
T
J
T
JRISE
T
A
+=
T
J
= Junction temperature
T
J(RISE)
= Rise in device junction temperature
over the ambient temperature
T
A
= Ambient temperature
Package
Package Type = TO-220-5
Input Voltage
V
IN
= 3.3V ± 5%
LDO Output Voltage and Current
V
OUT
= 2.5V
I
OUT
= 1000 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 1000 mA
P
LDO
= 1.028 Watts
T
J(RISE)
=P
TOTAL
x R
JA
T
J(RISE)
= 1.028 W x 29.3°C/W
T
J(RISE)
=30.12°C