MCP1726 Microchip Technology, MCP1726 Datasheet - Page 19

• Manufacturer Part Number: MCP1726
• Description: 1A Low Voltage / Low Quiescent Current LDO Regulator
• Manufacturer: Microchip Technology

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. The following equation
can be used to determine the package maximum inter-
nal power dissipation.
EQUATION 5-4:
EQUATION 5-5:
EQUATION 5-6:
© 2005 Microchip Technology Inc.
P
P
T
T
T
T
D(MAX)
D(MAX)
A(MAX)
J(RISE)
J(RISE)
J(MAX)
R
R
T
T
JA
JA
A
J
P
D MAX
= Maximum device power
= maximum continuous junction
= maximum ambient temperature
= Thermal resistance from junction
= Rise in device junction
= Maximum device power
= Thermal resistance from junction
= Junction temperature
= Rise in device junction
= Ambient temperature
T
J RISE
dissipation
temperature
to ambient
temperature over the ambient
temperature
dissipation
to ambient
temperature over the ambient
temperature
T
J
=
=
=
---------------------------------------------------
T
T
P
J RISE
J MAX
D MAX
R
+
–
JA
T
T
A
A MAX
R
JA
5.3
Internal power dissipation, junction temperature rise,
junction temperature and maximum power dissipation
is calculated in the following example. The power dissi-
pation as a result of ground current is small enough to
be neglected.
5.3.1
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 ther-
mal resistance from junction to ambient (R
derived from an EIA/JEDEC standard for measuring
thermal resistance for small surface-mount packages.
The EIA/JEDEC specification is JESD51-7 “High
Effective Thermal Conductivity Test Board for Leaded
Surface-Mount Packages”. 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.
Package
Input Voltage
LDO Output Voltage and Current
Maximum Ambient Temperature
Internal Power Dissipation
Package Type = 3X3DFN
P
T
LDO(MAX)
T
T
J(RISE)
T
JRISE
JRISE
A(MAX)
Typical Application
V
P
P
I
OUT
OUT
LDO
LDO
POWER DISSIPATION EXAMPLE
V
IN
= P
= 1.192 W x 41.0
= 48.8
= 3.3V ± 10%
= 2.5V
= 1.0A
= 70°C
= (V
= (3.3V x 1.1) – (0.975 x 2.5V))
= 1.192 Watts
TOTAL
x 1.0A
IN(MAX)
°
C
x R
– V
JA
MCP1726
OUT(MIN)
°
C/W
DS21936B-page 19
) x I
OUT(MAX)
JA
) is