MCP1726 datasheet(14/30 Pages) MICROCHIP

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MCP1726

DS21936B-page 14

4.0

DEVICE OVERVIEW

The MCP1726 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 220 mV at 1A of current makes

it ideal for battery-powered applications. Unlike other

high output current LDOs, the MCP1726 only draws

220 µA of quiescent current at full load.

4.1

LDO Output Voltage

The MCP1726 LDO is available with either a fixed

output voltage or an adjustable output voltage. The

output voltage range is 0.8V to 5.5V for both versions.

4.1.1

ADJUST INPUT

The adjustable version of the MCP1726 uses the ADJ

pin (pin 7) to get the output voltage feedback for output

voltage regulation. This allows the user to set the out-

put 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

MCP1726. 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 R1

yields the following equation:

EQUATION 4-2:

4.2

Output Current and Current

Limiting

The MCP1726 LDO is tested and ensured to supply a

minimum of 1A of output current. The MCP1726 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 MCP1726 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 1.7A (typical). If the over-

load condition is a soft overload, the MCP1726 will sup-

ply higher load currents of up to 3A. The MCP1726

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 1A 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 4.9 “Overtem-

perature

Protection”

for

information

overtemperature shutdown.

4.3

Output Capacitor

The MCP1726 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 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 accept-

able 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

MCP1726 to improve dynamic performance and power

supply ripple rejection performance. A maximum of

22 µF

recommended.

Aluminum-electrolytic

capacitors are not recommended for low-temperature

applications of < -25°C.

OUT

ADJ

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

⎝⎠

⎛⎞

VOUT = LDO Output Voltage

VADJ = ADJ Pin Voltage (typically 0.41V)

VIN

SHDN

GND

PWRGD

CDELAY

ADJ

VOUT

1µF

VOUT

4.7 µF

VIN

Off

VIN

1000 pF

MCP1726-ADJ

OUT

ADJ

–

ADJ

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

⎝⎠

⎛⎞

VOUT = LDO Output Voltage

VADJ = ADJ Pin Voltage (typically 0.41V)

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