Datasheet

MCP1727
DS21999B-page 20 © 2007 Microchip Technology Inc.
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.
FIGURE 5-1: Typical Application Circuit.
5.1.1 APPLICATION CONDITIONS
5.2 Power Calculations
5.2.1 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.
EQUATION 5-1:
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:
EQUATION 5-2:
The total power dissipated within the MCP1727 is the
sum of the power dissipated in the LDO pass device
and the P(I
GND
) term. Because of the CMOS
construction, the typical I
GND
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.
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 (Rθ
JA
) of the device. The thermal resistance
from junction to ambient for the 3x3 DFN package is
estimated at 41
° C/W.
EQUATION 5-3:
Package Type = 3x3DFN8
Input Voltage Range = 3.3V ± 5%
V
IN
maximum = 3.465V
V
IN
minimum = 3.135V
V
DROPOUT (max)
= 0.525V
V
OUT
(typical) = 2.5V
I
OUT
= 1.5A maximum
P
DISS
(typical) = 1.2W
Temperature Rise = 49.2
°C
V
IN
SHDN
GND
PWRGD
C
DELAY
Sense
V
OUT
1
2
3
4
5
6
7
8
10 µF
V
OUT
= 2.5V @ 1.5A
10 µF
V
IN
= 3.3V
On
Off
V
IN
R
1
C
1
C
2
1000 pF
C
3
MCP1727-2.5
10kΩ
PWRGD
P
LDO
V
IN MAX)()
V
OUT MIN()
–()I
OUT MAX)()
×=
Where:
P
LDO
= LDO Pass device internal
power dissipation
V
IN(MAX)
= Maximum input voltage
V
OUT(MIN)
= LDO minimum output voltage
P
IGND()
V
IN MAX()
I
VIN
×=
Where:
P
I(GND
= Power dissipation due to the
quiescent current of the LDO
V
IN(MAX)
= Maximum input voltage
I
VIN
= Current flowing in the V
IN
pin
with no LDO output current
(LDO quiescent current)
T
JMAX()
P
TOTAL
Rθ
JA
× T
AMAX
+=
T
J(MAX)
= Maximum continuous junction
temperature
P
TOTAL
= Total device power dissipation
Rθ
JA
= Thermal resistance from junction to
ambient
T
AMAX
= Maximum ambient temperature