MCP1825 datasheet(17/38 Pages) MICROCHIP

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DS22056B-page 17

MCP1825/MCP1825S

4.0

DEVICE OVERVIEW

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.

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.

4.1.1

ADJUST INPUT

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:

FIGURE 4-1:

Typical adjustable output

voltage application circuit.

The allowable resistance value range for resistor R2 is

from 10 k

Ω to 200 kΩ. Solving the equation for R

yields the following equation:

EQUATION 4-2:

4.2

Output Current and Current

Limiting

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.

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.

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.

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.

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.

Larger LDO output capacitors can be used with the

MCP1825/MCP1825S

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.

OUT

ADJ

------------------

⎝⎠

⎛⎞

Where:

VOUT

LDO Output Voltage

VADJ

=ADJ Pin Voltage

(typically 0.41V)

SHDN

GND

ADJ

1µF

VOUT

4.7 µF

VIN

Off

MCP1825-ADJ

3 4 5

OUT

ADJ

–

ADJ

--------------------------------

⎝⎠

⎛⎞

Where:

VOUT

LDO Output Voltage

VADJ

=ADJ Pin Voltage

(typically 0.41V)

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