Datasheet

© 2007 Microchip Technology Inc. DS22001C-page 19
MCP1827/MCP1827S
5.0 APPLICATION
CIRCUITS/ISSUES
5.1 Typical Application
The MCP1827/MCP1827S 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
MCP1827/MCP1827S 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
MCP1827/MCP1827S 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
MCP1827/MCP1827S is the sum of the power dissi-
pated in the LDO pass device and the P(I
GND
) term.
Because of the CMOS construction, the typical I
GND
for
the MCP1827/MCP1827S 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 MCP1827/MCP1827S is
+125
°C. To estimate the internal junction temperature
of the MCP1827/MCP1827S, 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 TO-220-5
package is estimated at 29.3
° C/W.
EQUATION 5-3:
Package Type = TO-220-5
Input Voltage Range = 3.3V ± 5%
V
IN
maximum = 3.465V
V
IN
minimum = 3.135V
V
DROPOUT (max)
= 0.550V
V
OUT
(typical) = 2.5V
I
OUT
= 1.5A maximum
P
DISS
(typical) = 1.2W
Temperature Rise = 35.2
°C
10 µF
V
OUT
= 2.5V @ 1.5A
R
1
C
2
10 kΩ
PWRGD
SHDN
GND
2
4.7 µF
On
Off
C
1
MCP1827-2.5
1
3
4
5
3.3V
V
IN
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