MCP1727
EQUATION 4-2:
R1 = R2
4.0
DEVICE OVERVIEW
VOUT – VADJ
--------------------------------
VADJ
⎛
⎝
⎞
⎠
The MCP1727 is a high output current, Low Dropout
(LDO) voltage regulator with an adjustable delay
power-good output and shutdown control input. The
low dropout voltage of 330 mV typical at 1.5A of current
makes it ideal for battery-powered applications. Unlike
other high output current LDOs, the MCP1727 only
draws a maximum of 220 µA of quiescent current.
Where:
VOUT
VADJ
=
=
LDO Output Voltage
ADJ Pin Voltage
(typically 0.41V)
4.2
Output Current and Current
Limiting
4.1
LDO Output Voltage
The MCP1727 LDO is available with either a fixed
output voltage or an adjustable output voltage. The
output voltage range is 0.8V to 5.0V for both versions.
The MCP1727 LDO is tested and ensured to supply a
minimum of 1.5A of output current. The MCP1727 has
no minimum output load, so the output load current can
go to 0 mA and the LDO will continue to regulate the
output voltage to within tolerance.
4.1.1
ADJUST INPUT
The adjustable version of the MCP1727 uses the ADJ
pin (pin 7) to get the output voltage feedback for output
voltage regulation. This allows the user to set the
output voltage of the device with two external resistors.
The nominal voltage for ADJ is 0.41V.
The MCP1727 also incorporates an output current limit.
If the output voltage falls below 0.7V due to an overload
condition (usually represents a shorted load condition),
the output current is limited to 2.2A (typical). If the
overload condition is a soft overload, the MCP1727 will
supply higher load currents of up to 3A. The MCP1727
should not be operated in this condition continuously as
it may result in failure of the device. However, this does
allow for device usage in applications that have higher
pulsed load currents having an average output current
value of 1.5A or less.
Figure 4-1 shows the adjustable version of the
MCP1727. Resistors R1 and R2 form the resistor
divider network necessary to set the output voltage.
With this configuration, the equation for setting VOUT is:
EQUATION 4-1:
R1 + R2
⎛
⎝
⎞
⎠
------------------
VOUT = VADJ
Output overload conditions may also result in an over-
temperature shutdown of the device. If the junction
temperature rises above 150°C, the LDO will shut
down the output voltage. See Section 4.9 “Overtem-
perature Protection” for more information on
overtemperature shutdown.
R2
Where:
VOUT
VADJ
=
=
LDO Output Voltage
ADJ Pin Voltage
(typically 0.41V)
4.3
Output Capacitor
MCP1727-ADJ
The MCP1727 requires a minimum output capacitance
of 1 µF for output voltage stability. Ceramic capacitors
are recommended because of their size, cost and
environmental robustness qualities.
V
V
OUT
IN
V
V
1
2
3
4
V
8
7
6
IN
IN
OUT
C
4.7 µF
1
ADJ
R
1
C2
1 µF
SHDN
GND
C
DELAY
PWRGD 5
Aluminum-electrolytic and tantalum capacitors can be
used on the LDO output as well. The Equivalent Series
Resistance (ESR) of the electrolytic output capacitor
must be no greater than 1 ohm. The output capacitor
should be located as close to the LDO output as is
practical. Ceramic materials X7R and X5R have low
temperature coefficients and are well within the
acceptable ESR range required. A typical 1 µF X7R
0805 capacitor has an ESR of 50 milli-ohms.
On
Off
C
3
R
2
1000 pF
FIGURE 4-1:
voltage application circuit.
Typical adjustable output
The allowable resistance value range for resistor R2 is
from 10 kΩ to 200 kΩ. Solving the equation for R1
yields the following equation:
Larger LDO output capacitors can be used with the
MCP1727 to improve dynamic performance and power
supply ripple rejection performance. A maximum of
22 µF
is
recommended.
Aluminum-electrolytic
capacitors are not recommended for low-temperature
applications of ≤ 25°C.
DS21999B-page 16
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
