MCP1754 Microchip Technology Inc., MCP1754 Datasheet - Page 22

• Manufacturer Part Number: MCP1754
• Description: 150 Ma, 16v, High Performance Ldo
• Manufacturer: Microchip Technology Inc.

MCP1754/MCP1754S
5.3
Internal power dissipation, junction temperature rise,
junction temperature and maximum power dissipation
are calculated in the following example. The power
dissipation, 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 thermal
resistance from junction to ambient (Rθ
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
Application”, (DS00792), for more information regarding
this subject.
Junction Temperature Estimate
To estimate the internal junction temperature, the
calculated temperature rise is added to the ambient or
offset temperature. For this example, the worst-case
junction temperature is estimated below.
DS22276A-page 22
Package
Package Type = SOT23
Input Voltage
LDO Output Voltages and Currents
Maximum Ambient Temperature
Internal Power Dissipation
Internal Power dissipation is the product of the LDO
output current times the voltage across the LDO
(V
IN
P
to V
T
LDO(MAX)
T
T
J(RISE)
T
JRISE
JRISE
A(MAX)
Voltage Regulator
OUT
V
P
P
I
OUT
OUT
LDO
LDO
V
POWER DISSIPATION EXAMPLE
IN
).
= P
= 152.7 milliwatts x 336.0
= 51.3
= 3.6V to 4.8V
= 1.8V
= 50 mA
= +40°C
= (V
= (4.8V - (0.97 x 1.8V)) x 50 mA
= 152.7 milli-Watts
TOTAL
IN(MAX)
°
C
x Rq
- V
JA
OUT(MIN)
) x I
°
JA
C/Watt
) is derived
OUT(MAX)
Maximum Package Power Dissipation Examples at
+40°C Ambient Temperature
5.4
The MCP1754/MCP1754S can be used not only as a
regulator, but also as a low quiescent current voltage
reference. In many microcontroller applications, the
initial accuracy of the reference can be calibrated using
production test equipment or by using a ratio
measurement. When the initial accuracy is calibrated,
the thermal stability and line regulation tolerance are
the
MCP1754S LDO. The low cost, low quiescent current
and small ceramic output capacitor are all advantages
when using the MCP1754/MCP1754S as a voltage
reference.
FIGURE 5-2:
as a Voltage Reference.
5.5
For some applications, there are pulsed load current
events that may exceed the specified 150 mA
maximum specification of the MCP1754/MCP1754S.
The internal current limit of the MCP1754/MCP1754S
will prevent high peak load demands from causing non-
recoverable damage. The 150 mA rating is a maximum
average continuous rating. As long as the average
current does not exceed 150 mA, pulsed higher load
currents can be applied to the MCP1754/MCP1754S
The typical current limit for the MCP1754/MCP1754S is
250 mA (T
SOT23 (336.0°C/Watt = Rθ
SOT89 (153.3°C/Watt = Rθ
56 µA Bias
C
1 µF
IN
P
P
P
P
only
D(MAX)
D(MAX)
D(MAX)
D(MAX)
Bridge Sensor
Voltage Reference
Pulsed Load Applications
MCP1754S
A
T
T
GND
V
errors
+25°C).
J
J
IN
= T
= 91.3°C
= (125°C - 40°C) / 336°C/W
= 253 milliwatts
= (125°C - 40°C) / 153.3°C/W
= 554 milliwatts
V
OUT
Ratio Metric Reference
JRISE
Using the MCP1754/MCP1754S
introduced
C
1 µF
OUT
+ T
© 2011 Microchip Technology Inc.
A(MAX)
JA
JA
)
)
by
V
ADO
AD1
the
microcontroller
REF
PICmicro
MCP1754/
®
.