MCP1825/MCP1825S
EQUATION 4-2:
4.0
DEVICE OVERVIEW
VOUT – VADJ
⎛
⎝
⎞
⎠
The MCP1825/MCP1825S is a high output current,
Low Dropout (LDO) voltage regulator. The low dropout
voltage of 210 mV typical at 500 mA of current makes
it ideal for battery-powered applications. Unlike other
high output current LDOs, the MCP1825/MCP1825S
only draws a maximum of 220 µA of quiescent current.
The MCP1825 has a shutdown control input and a
power good output.
--------------------------------
R1 = R2
VADJ
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 5-pin MCP1825 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 3-pin MCP1825S LDO is available as a fixed
voltage device.
The MCP1825/MCP1825S LDO is tested and ensured
to supply a minimum of 500 mA of output current. The
MCP1825/MCP1825S 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 MCP1825/MCP1825S 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 1.2A
(typical). If the overload condition is a soft overload, the
MCP1825/MCP1825S will supply higher load currents
of up to 1.5A. The MCP1825/MCP1825S 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
500 mA or less.
The adjustable version of the MCP1825 uses the ADJ
pin (pin 5) 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.
Figure 4-1 shows the adjustable version of the
MCP1825. 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:
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 4.8 “Overtem-
perature Protection” for more information on
overtemperature shutdown.
R1 + R2
⎛
⎝
⎞
⎠
------------------
VOUT = VADJ
R2
Where:
VOUT
VADJ
=
=
LDO Output Voltage
ADJ Pin Voltage
(typically 0.41V)
4.3
Output Capacitor
The MCP1825/MCP1825S 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.
MCP1825-ADJ
V
OUT
On
R
1
C2
1 µF
1
3
2 4
5
Off
SHDN
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.
ADJ
V
IN
C
R
1
2
GND
4.7 µF
FIGURE 4-1:
Typical adjustable output
voltage application circuit.
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
MCP1825/MCP1825S
to
improve
dynamic
performance and power supply ripple rejection
performance. A maximum of 22 µF is recommended.
Aluminum-electrolytic capacitors are not recom-
mended for low temperature applications of < -25°C.
© 2008 Microchip Technology Inc.
DS22056B-page 17
MICROCHIP [ MICROCHIP ]
