MAX8863 Просмотр технического описания (PDF) - ON Semiconductor

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MAX8863

Pin-Compatible, Low-Dropout, 120 mA Linear Regulator

ON Semiconductor 

MAX8863

Shutdown

Low input on SHDN shuts down the MAX8863 by

turning off the pass transistor, control circuit, reference, and

all biases. This reduces the supply current to 0.1 nA, typical.

For normal operation, connect SHDN to IN. When the

MAX8863 is placed in shutdown mode, the output voltage

is actively discharged to ground.

Current Limit

The current limiter on the MAX8863 monitors and

controls the pass transistor’s gate voltage. It estimates the

output current, limiting it to 280 mA. The current limit

should be considered 150 mA (min) to 410 mA (max) for

design purposes. The output can be shorted to ground

indefinitely without damaging the device.

Thermal Overload Protection

The MAX8863 features thermal overload protection,

which limits total power dissipation. The thermal sensor

signals the shutdown logic to turn off the pass transistor

when the junction temperature exceeds TJ = +170°C. This

allows the IC’s junction temperature to cool by 20°C before

the thermal sensor turns the pass transistor back on. This

results in a pulsed output during continuous thermal

overload conditions.

This feature is designed to protect the MAX8863 during

thermal events. High load currents and high input–output

differential voltages may cause a momentary overshoot of

2.0% to 8.0% for 200 msec when the load is removed. This

can be avoided by raising the minimum load current from

0 µA (+125°C) to 100 µA (+150°C). The maximum

junction temperature rating of +150°C should not be

exceeded for continuous operation.

Operating Region and Power Dissipation

The MAX8863’s maximum power dissipation depends on

the thermal resistance of the case and circuit board, the rate

of air flow, and the temperature difference between the die

junction and ambient air. The devices’ power dissipation is

P = IOUT (VIN – VOUT); resulting maximum power

dissipation is:

PMAX + (TJ * TA)ńQJA

where (TJ – TA) is the temperature difference between the

devices’ die junction and the surrounding air, and QJA is the

thermal resistance of the chosen package to the surrounding

air.

The devices’ GND pin provides an electrical connection

to ground and channels heat away. The GND pin should be

connected to ground with a large pad or ground plane.

APPLICATIONS INFORMATION

Capacitor Selection and Regulator Stability

A 1.0 µF capacitor on the input, and a 1.0 µF capacitor on

the output should generally be used on the MAX8863. For

better supply–noise rejection and transient response, larger

input capacitor values and lower ESR should be used. If the

device is several inches from the power source or if large,

fast transients are expected, a higher–value input capacitor

(10 µF) may be required.

Using large output capacitors may improve load–transient

response, stability, and power–supply rejection. A minimum

of 1.0 µF is recommended for stable operation over the full

temperature range with load currents up to 120 mA.

Noise

During normal operation, the MAX8863 have low

(350 µVRMS) output noise. The ADC’s power–supply

rejection specifications should be considered for

applications that include analog–to–digital converters of

greater than 12 bits.

Power–Supply Rejection and Operation from

Sources Other than Batteries

Power–supply rejection for the MAX8863 is 62 dB at low

frequencies, rolling off above 300 Hz. Power supply noise

rejection is primarily controlled by the output capacitor at

frequencies of more than 20 KHz.

Supply noise rejection and transient response can be

improved when operating from sources other than batteries

by increasing the values of the input and output capacitors,

and using passive filtering techniques.

Load Transient Considerations

With the MAX8863, typical overshoot for step changes in

the load current from 0 mA to 50 mA is 12 mV. To lessen

transient spikes, increase the output capacitor’s value, and

decrease its ESR.

Input–Output (Dropout) Voltage

A regulator’s dropout voltage determines the lowest

usable supply voltage. This determines the useful

end–of–life battery voltage for battery–powered systems.

Since the MAX8863 uses a P–channel MOSFET pass

transistor, the devices’ dropout voltage is a function of

RDS(ON) multiplied by the load current.

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