MCP1702 Microchip Technology, MCP1702 Datasheet - Page 14

• Manufacturer Part Number: MCP1702
• Description: 250 mA Low Quiescent Current LDO Regulator
• Manufacturer: Microchip Technology

MCP1702
6.3
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.
6.3.1
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
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 SOT-23 Can Dissipate in an
Application”, (DS00792), for more information regarding
this subject.
DS22008B-page 14
Package
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
T
P
T
T
J(RISE)
to V
Package
LDO(MAX)
JRISE
JRISE
T
A(MAX)
Voltage Regulator
OUT
V
P
P
Type
I
OUT
OUT
LDO
LDO
POWER DISSIPATION EXAMPLE
V
IN
).
= P
= 218.1 milli-Watts x 336.0
= 73.3
=
=
=
=
=
=
=
=
TOTAL
SOT-23A
2.8V to 3.2V
1.8V
150 mA
+40°C
(V
I
(3.2V - (0.97 x 1.8V)) x 150 mA
218.1 milli-Watts
OUT(MAX)
°
C
IN(MAX)
x Rq
JA
- V
OUT(MIN)
JA
°
) x
) is derived
C/Watt
Effective
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.
Maximum Package Power Dissipation at +40°C
Ambient Temperature
6.4
The MCP1702 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 only errors introduced
by the MCP1702 LDO. The low-cost, low quiescent
current and small ceramic output capacitor are all
advantages when using the MCP1702 as a voltage
reference.
FIGURE 6-2:
voltage reference.
SOT-23 (336.0°C/Watt = Rθ
SOT-89 (52°C/Watt = Rθ
TO92 (131.9°C/Watt = Rθ
C
1 µF
IN
2 µA Bias
P
P
P
P
P
P
Bridge Sensor
Voltage Reference
D(MAX)
D(MAX)
D(MAX)
D(MAX)
D(MAX)
D(MAX)
MCP1702
V
GND
IN
T
T
V
J
J
OUT
Ratio Metric Reference
= T
= 113.3°C
=
=
=
=
=
=
C
1 µF
JRISE
Using the MCP1702 as a
(125°C - 40°C) / 336°C/W
253 milli-Watts
(125°C - 40°C) / 52°C/W
1.635 Watts
(125°C - 40°C) / 131.9°C/W
644 milli-Watts
OUT
© 2007 Microchip Technology Inc.
JA
JA
)
+ T
JA
)
)
A(MAX)
V
ADO
AD1
Microcontroller
REF
PIC
®