Dual, Low-Dropout, 100mA Linear Regulators

10

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Reverse Battery Protection

The MAX8865/MAX8866 have a unique protection

scheme that limits the reverse supply current to less

ground. The circuitry monitors the polarity of these

pins, disconnecting the internal circuitry and parasitic

diodes when the battery is reversed. This feature pre-

vents the device from overheating and damaging the

battery.

__________Applications Information

Capacitor Selection and

Regulator Stability

Normally, use two 1µF surface-mount ceramic capaci-

tors on the input and a 1µF surface-mount ceramic

capacitor on each output of the MAX8865/MAX8866.

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 cur-

rents of 100mA, a minimum of 1µF is recommended

graph in the

Typical Operating Characteristics).

Noise

normal operation. When using the MAX8865/MAX8866

in applications that include analog-to-digital converters

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

ply 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 MAX8865/MAX8866 are designed to deliver low

dropout voltages and low quiescent currents in battery-

powered systems. Power-supply rejection is 60dB at low

frequencies and rolls off above 400Hz. As the frequency

increases above 100kHz, the output capacitor is the

major contributor to the rejection of power-supply noise

(see the Power-Supply Rejection Ratio vs. 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 capac-

itors, and using passive filtering techniques (see the

supply and load-transient responses in the

Typical

Operating Characteristics).

Load-Transient Considerations

The MAX8865/MAX8866 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.

Cross-Regulation

Cross-regulation refers to the change in one output

voltage when the load changes on the other output. For

the MAX8865/MAX8866, cross-regulation for a 0mA to

50mA load change on one side results in less than 1mV

change of output voltage. If the power dissipation on

one output causes the junction temperature to exceed

125°C, ensure regulation of the other output with a mini-

mum load current of 100µA.

Input-Output (Dropout) Voltage

A regulator’s minimum input-output voltage differential (or

dropout voltage) determines the lowest usable supply volt-

age. In battery-powered systems, this will determine the

useful end-of-life battery voltage. Because the

MAX8865/MAX8866 use P-channel MOSFET pass transis-

plied by the load currents (see

Electrical Characteristics).

___________________Chip Information

TRANSISTOR COUNT: 259