MCP1727
In addition to the LDO pass element power dissipation,
there is power dissipation within the MCP1727 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 MCP1727 is used for applications that require high
LDO output current and a power good output.
EQUATION 5-2:
PI(GND) = VIN(MAX) × IVIN
Where:
MCP1727-2.5
V
= 3.3V
V
= 2.5V @ 1.5A
IN
OUT
PI(GND
=
Power dissipation due to the
quiescent current of the LDO
1
2
3
4
V
V
V
OUT
8
7
6
5
IN
IN
C
R
1
1
Sense
10 µF
C
2
10 µF
10kΩ
VIN(MAX)
IVIN
=
=
Maximum input voltage
SHDN C
DELAY
GND PWRGD
Current flowing in the VIN pin
with no LDO output current
(LDO quiescent current)
On
Off
C
3
1000 pF
The total power dissipated within the MCP1727 is the
sum of the power dissipated in the LDO pass device
PWRGD
and the P(IGND
) term. Because of the CMOS
construction, the typical IGND for the MCP1727 is
120 µA. Operating at a maximum of 3.465V results in a
power dissipation of 0.49 milli-Watts. 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 = 3x3DFN8
The maximum continuous operating junction
temperature specified for the MCP1727 is +125°C. To
estimate the internal junction temperature of the
MCP1727, 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 3x3 DFN package is
estimated at 41° C/W.
Input Voltage Range = 3.3V ± 5%
IN maximum = 3.465V
IN minimum = 3.135V
VDROPOUT (max) = 0.525V
OUT (typical) = 2.5V
OUT = 1.5A maximum
V
V
V
I
PDISS (typical) = 1.2W
EQUATION 5-3:
Temperature Rise = 49.2°C
TJ(MAX) = PTOTAL × RθJA + TAMAX
5.2
Power Calculations
TJ(MAX) = Maximum continuous junction
temperature
5.2.1
POWER DISSIPATION
PTOTAL = Total device power dissipation
The internal power dissipation within the MCP1727 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.
RθJA = Thermal resistance from junction to
ambient
TAMAX = Maximum ambient temperature
EQUATION 5-1:
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
DS21999B-page 20
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
