MAX8863 Просмотр технического описания (PDF) - Maxim Integrated

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MAX8863

Low-Dropout, 120mA Linear Regulators

Maxim Integrated 

MAX8863T/S/R,

MAX8864T/S/R

Low-Dropout, 120mA Linear Regulators

Operating Region and Power Dissipation

Maximum power dissipation of the MAX8863/MAX8864

depends on the thermal resistance of the case and circuit

board, the temperature difference between the die junction

and ambient air, and the rate of air flow. The power

dissipation across the device is P = IOUT (VIN - VOUT).

The resulting maximum power dissipation is:

PMAX = (TJ - TA) / θJA

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

MAX8863/MAX8864 die junction and the surrounding air,

and θJA is the thermal resistance of the chosen package

to the surrounding air.

The GND pin of the MAX8863/MAX8864 performs the

dual function of providing an electrical connection to

ground and channeling heat away. Connect the GND pin

to ground using a large pad or ground plane.

Reverse Battery Protection

The MAX8863/MAX8864 have a unique protection

scheme that limits the reverse supply current to less than

1mA when either VIN or VSHDN falls below ground. The

circuitry monitors the polarity of these two pins,

disconnecting the internal circuitry and parasitic diodes

when the battery is reversed. This feature prevents the

device from overheating and damaging the battery.

VIN > 5.5V Minimum Load Current

When operating the MAX8863/MAX8864 with an input

voltage above 5.5V, a minimum load current of 20μA is

required to maintain regulation in preset voltage mode.

When setting the output with external resistors, the

minimum current through the external feedback resistors

and load must be 30μA.

Applications Information

Capacitor Selection and Regulator Stability

Normally, use a 1μF capacitor on the input and a 1μF

capacitor on the output of the MAX8863/MAX8864.

Larger input capacitor values and lower ESR provide

better supply-noise rejection and transient response. A

higher-value input capacitor (10μF) may be necessary

if large, fast transients are anticipated and the device is

located several inches from the power source. Improve

load-transient response, stability, and power-supply rejection

by using large output capacitors. For stable operation

over the full temperature range, with load currents up to

120mA, a minimum of 1μF is recommended.

Noise

The MAX8863/MAX8864 exhibit 350μVRMS noise during

normal operation. When using the MAX8863/MAX8864

in applications that include analog-to-digital converters

of greater than 12 bits, consider the ADC’s power-supply

rejection specifications (see the Output Noise DC to

1MHz photo in the Typical Operating Characteristics).

Power-Supply Rejection and Operation

from Sources Other than Batteries

The MAX8863/MAX8864 are designed to deliver low

dropout voltages and low quiescent currents in battery-

powered systems. Power-supply rejection is 62dB at low

frequencies and rolls off above 300Hz. As the frequency

increases above 20kHz, the output capacitor is the major

contributor to the rejection of power-supply noise (see

the Power-Supply Rejection Ratio vs. Ripple Frequency

graph in the Typical Operating Characteristics).

When operating from sources other than batteries,

improve supply-noise rejection and transient response by

increasing the values of the input and output capacitors,

and using passive filtering techniques (see the supply

and load-transient responses in the Typical Operating

Characteristics).

Load Transient Considerations

The MAX8863/MAX8864 load-transient response

graphs (see Typical Operating Characteristics) show two

components of the output response: a DC shift of the

output voltage due to the different load currents, and the

transient response. Typical overshoot for step changes in

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

the output capacitor’s value and decreasing its ESR

attenuates transient spikes.

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