Datasheet

 2012 Microchip Technology Inc. DS25160A-page 17
MCP1755/1755S
4.0 DEVICE OVERVIEW
The MCP1755/1755S is a 300 mA output current, low-
dropout (LDO) voltage regulator. The low-dropout
voltage of 300 mV typical at 300 mA of current makes
it ideal for battery-powered applications. The input
voltage range is 3.6V to 16.0V. Unlike other high output
current LDOs, the MCP1755/1755S typically draws
only 300 µA of quiescent current for a 300 mA load.
The MCP1755 adds a shutdown control input pin and a
power good output pin. The output voltage options are
fixed.
4.1 LDO Output Voltage
The MCP1755 LDO has a fixed output voltage. The
output voltage range is 1.8V to 5.5V. The MCP1755S
LDO is available as a fixed voltage device.
4.2 Output Current and
Current Limiting
The MCP1755/1755S LDO is tested and ensured to
supply a minimum of 300 mA of output current. The
MCP1755/1755S 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.
The MCP1755/1755S also incorporates a true output
current foldback. If the output load presents an
excessive load due to a low-impedance short circuit
condition, the output current and voltage will fold back
towards 30 mA and 0V, respectively. The output
voltage and current will resume normal levels when the
excessive load is removed. If the overload condition is
a soft overload, the MCP1755/1755S will supply higher
load currents of up to typically 350 mA. This allows for
device usage in applications that have pulsed load
currents having an average output current value of
300 mA or less.
Output overload conditions may also result in an
overtemperature shutdown of the device. If the junction
temperature rises above +150°C (typical), the LDO will
shut down the output. See Section 4.8,
Overtemperature Protection for more information on
overtemperature shutdown.
FIGURE 4-1: Typical Current Foldback.
4.3 Output Capacitor
The MCP1755/1755S 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.
Aluminum-electrolytic and tantalum capacitors can be
used on the LDO output as well. The Equivalent Series
Resistance (ESR) of the electrolytic output capacitor
should be no greater than 2 ohms. 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.
Larger LDO output capacitors can be used with the
MCP1755/1755S to improve dynamic performance
and power supply ripple rejection performance. A
maximum of 1000 µF is recommended. Aluminum-
electrolytic capacitors are not recommended for low
temperature applications of < -25°C.
4.4 Input Capacitor
Low input source impedance is necessary for the LDO
output to operate properly. When operating from
batteries, or in applications with long lead length
(> 10 inches) between the input source and the LDO,
some input capacitance is recommended. A minimum
of 1.0 µF to 4.7 µF is recommended for most
applications.
For applications that have output step load
requirements, the input capacitance of the LDO is very
important. The input capacitance provides the LDO
with a good local low-impedance source to pull the
transient currents from, in order to respond quickly to
the output load step. For good step response
performance, the input capacitor should be of
equivalent or higher value than the output capacitor.
The capacitor should be placed as close to the input of
the LDO as is practical. Larger input capacitors will also
help reduce any high-frequency noise on the input and
output of the LDO and reduce the effects of any
inductance that exists between the input source
voltage and the input capacitance of the LDO.
2.0
3.0
4.0
5.0
6.0
u
tput Voltage (V)
V
IN
= 6.0V
V
OUT
= 5.0V
0.0
1.0
0 0.1 0.2 0.3 0.4 0.5
O
u
Output Current (A)
Increasing Load
Decreasing Load