MCP1825/MCP1825S
In addition to the LDO pass element power dissipation,
there is power dissipation within the MCP1825/
MCP1825S as a result of quiescent or ground current.
The power dissipation as a result of the ground current
can be calculated using the following equation:
5.0
APPLICATION CIRCUITS/
ISSUES
5.1
Typical Application
The MCP1825/MCP1825S is used for applications that
require high LDO output current and a power good
output.
EQUATION 5-2:
PI(GND) = VIN(MAX) × IVIN
Where:
V
= 2.5V @ 500 mA
OUT
R
PI(GND
=
Power dissipation due to the
quiescent current of the LDO
MCP1825-2.5
On
1
C
1
3
2 4
5
2
VIN(MAX)
IVIN
=
=
Maximum input voltage
10 kΩ
Off
SHDN
10 µF
Current flowing in the VIN pin
with no LDO output current
(LDO quiescent current)
V
IN
3.3V
C
1
4.7 µF
PWRGD
GND
The total power dissipated within the MCP1825/
MCP1825S is the sum of the power dissipated in the
LDO pass device and the P(IGND) term. Because of the
CMOS construction, the typical IGND for the MCP1825/
MCP1825S is 120 µA. Operating at a maximum VIN of
3.465V results in a power dissipation of 0.12 milli-Watts
for a 2.5V output. For most applications, this is small
compared to the LDO pass device power dissipation
and can be neglected.
FIGURE 5-1:
Typical Application Circuit.
5.1.1 APPLICATION CONDITIONS
Package Type
Input Voltage Range
IN maximum
IN minimum
=
=
=
=
=
=
=
=
=
TO-220-5
3.3V ± 5%
3.465V
V
V
3.135V
The maximum continuous operating junction
temperature specified for the MCP1825/MCP1825S is
+125°C. To estimate the internal junction temperature
of the MCP1825/MCP1825S, the total internal power
dissipation is multiplied by the thermal resistance from
junction to ambient (RθJA) of the device. The thermal
resistance from junction to ambient for the TO-220-5
package is estimated at 29.3°C/W.
VDROPOUT (max)
VOUT (typical)
IOUT
0.350V
2.5V
500 mA maximum
0.483W
PDISS (typical)
Temperature Rise
14.2°C
5.2
Power Calculations
EQUATION 5-3:
TJ(MAX) = PTOTAL × RθJA + TAMAX
5.2.1
POWER DISSIPATION
The internal power dissipation within the MCP1825/
MCP1825S is a function of input voltage, output
voltage, output current and quiescent current.
Equation 5-1 can be used to calculate the internal
power dissipation for the LDO.
TJ(MAX) = Maximum continuous junction
temperature
PTOTAL = Total device power dissipation
RθJA = Thermal resistance from junction to
ambient
EQUATION 5-1:
TAMAX = Maximum ambient temperature
PLDO = (VIN(MAX)) – VOUT(MIN)) × IOUT(MAX))
Where:
PLDO
=
LDO Pass device internal
power dissipation
VIN(MAX)
=
=
Maximum input voltage
VOUT(MIN)
LDO minimum output voltage
DS22056B-page 20
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
