Datasheet

 2012 Microchip Technology Inc. DS25160A-page 21
MCP1755/1755S
5.0 APPLICATION CIRCUITS
AND ISSUES
5.1 Typical Application
The MCP1755/1755S is most commonly used as a
voltage regulator. The low quiescent current and low
dropout voltage make it ideal for many battery-powered
applications.
FIGURE 5-1: Typical Application Circuit.
5.1.1 APPLICATION INPUT CONDITIONS
5.2 Power Calculations
5.2.1 POWER DISSIPATION
The internal power dissipation of the MCP1755/1755S
is a function of input voltage, output voltage and output
current. The power dissipation, as a result of the
quiescent current draw, is so low, it is insignificant
(68.0 µA x V
IN
). The following equation can be used to
calculate the internal power dissipation of the LDO.
EQUATION 5-1:
The maximum continuous operating junction
temperature specified for the MCP1755/1755S is
+150°C. To estimate the internal junction temperature
of the MCP1755/1755S, the total internal power
dissipation is multiplied by the thermal resistance from
junction to ambient (R
JA
). The thermal resistance from
junction to ambient for the SOT-23 package is
estimated at 336
°C/W.
EQUATION 5-2:
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
internal power dissipation.
EQUATION 5-3:
EQUATION 5-4:
EQUATION 5-5:
Package Type = SOT-23
Input Voltage Range = 3.6V to 4.8V
V
IN
maximum = 4.8V
V
OUT
typical = 1.8V
I
OUT
= 50 mA maximum
GND
V
OUT
V
IN
C
IN
1µF Ceramic
C
OUT
1µF Ceramic
V
OUT
V
IN
3.6V to 4.8V
1.8V
I
OUT
50 mA
MCP1755S
P
LDO
V
IN MAX 
V
OUT MIN
–I
OUT MAX 
=
P
LDO
= LDO Pass device internal power
dissipation
V
IN(MAX)
= Maximum input voltage
V
OUT(MIN)
= LDO minimum output voltage
T
JMAX
P
TOTAL
R 
JA
 T
AMAX
+=
T
J(MAX)
= Maximum continuous junction
temperature
P
TOTAL
= Total device power dissipation
R
JA
= Thermal resistance from junction
to ambient
T
AMAX
= Maximum ambient temperature
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