Datasheet

 2009-2013 Microchip Technology Inc. DS20002200D-page 21
MCP1804
6.0 APPLICATION CIRCUITS AND
ISSUES
6.1 Typical Application
The MCP1804 is most commonly used as a voltage
regulator. Its low quiescent current and wide input
voltage make it ideal for Li-Ion and 12V 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 MCP1804 is a
function of input voltage, output voltage and output
current. The power dissipation resulting from the
quiescent current draw is so low it is insignificant
(50.0 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 MCP1804 is +85
°C. To estimate the
internal junction temperature of the MCP1804, 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 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:
EQUATION 6-5:
Package Type = SOT-23
Input Voltage Range = 3.8V to 4.2V
V
IN
maximum = 4.6V
V
OUT
typical = 1.8V
I
OUT
= 50 mA maximum
GND
V
OUT
V
IN
C
IN
1µF
C
OUT
1µF Ceramic
V
OUT
V
IN
4.2V
1.8V
I
OUT
50 mA
Ceramic
SHDN
NC
MCP1804
P
LDO
V
IN MAX
V
OUT MIN
–I
OUT
 =
Where:
P
LDO
= Internal power dissipation of the LDO
Pass device
V
IN(MAX)
= Maximum input voltage
V
OUT(MIN)
= Minimum output voltage of the LDO
T
JMAX
P
TOTAL
R 
JA
 T
AMAX
+=
Where:
T
J(MAX)
= Maximum continuous junction
temperature
P
TOTAL
= Total power dissipation of the device
R
JA
= Thermal resistance from junction to
ambient
T
A(MAX)
= Maximum ambient temperature
P
DMAX
T
JMAX
T
AMAX
–
R

JA
---------------------------------------------------=
Where:
P
D(MAX)
= Maximum power dissipation of the
device
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 the device’s junction
temperature over the ambient
temperature
P
D(MAX)
= Maximum power dissipation of the
device
R
JA
= Thermal resistance from junction to
ambient
T
J
T
JRISE
T
A
+=
Where:
T
J
= Junction Temperature
T
J(RISE)
= Rise in the device’s junction
temperature over the ambient
temperature
T
A
= Ambient temperature