2010 Microchip Technology Inc. DS22051D-page 17
MCP1801
6.0 APPLICATION CIRCUITS AND
ISSUES
6.1 Typical Application
The MCP1801 is most commonly used as a voltage
regulator. Its low quiescent current and low dropout
voltage make it ideal for many battery-powered
applications.
FIGURE 6-1: Typical Application Circuit.
6.1.1 APPLICATION INPUT CONDITIONS
6.2 Power Calculations
6.2.1 POWER DISSIPATION
The internal power dissipation of the MCP1801 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
(25.0 µA x V
IN
). The following equation can be used to
calculate the internal power dissipation of the LDO.
EQUATION 6-1:
The maximum continuous operating temperature
specified for the MCP1801 is +85°C
. To estimate the
internal junction temperature of the MCP1801, 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-23-5
pin package is estimated at 256°C/W.
EQUATION 6-2:
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 6-3:
EQUATION 6-4:
Package Type = SOT-23-5
Input Voltage Range = 2.4V to 5.0V
V
IN
maximum = 5.0V
V
OUT
typical = 1.8V
I
OUT
= 50 mA maximum
MCP1801
GND
V
OUT
V
IN
C
IN
1µF
C
OUT
1µF Ceramic
V
OUT
V
IN
2.4V to 5.0V
1.8V
I
OUT
50 mA
SHDN
Ceramic
NC
P
LDO
V
IN MAX
V
OUT MIN
–I
OUT M AX
=
Where:
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
+=
Where:
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
---------------------------------------------------
=
Where:
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
=
Where:
T
J(RISE)
= Rise in device junction
temperature over the ambient
temperature
P
TOTAL
= Maximum device power
dissipation
R
JA
= Thermal resistance from
junction to ambient
