quiescent current at no load and 220µA with 100mA

load current on both outputs (see the Typical Operating

Characteristics). A PNP-based regulator has a high

dropout voltage that is independent of the load. A P-

channel MOSFET’s dropout voltage is proportional to

load current, providing for low dropout voltage at heavy

loads and extremely low dropout at lighter loads.

Current Limit

The MAX8559 contains two independent current lim-

iters, one for each regulator output, monitoring and

controlling the pass transistor’s gate voltage and limit-

ing the output current to 310mA (min). The outputs can

be shorted to ground continuously without damaging

the part.

Low-Noise Operation

An external 0.01µF bypass capacitor at BP in conjunc-

tion with an internal resistor creates a lowpass filter.

Typical Operating Characteristics show a graph of

Output-Noise Spectral Density with these values. If out-

put noise is not critical, the BP capacitor can be

removed to reduce total solution size and cost.

Shutdown

The MAX8559 has independent shutdown control

inputs (SHDNA and SHDNB). Drive SHDNA low to shut

down OUTA. Drive SHNDB low to shut down OUTB.

Drive both SHDNA and SHDNB low to shut down the

entire chip, reducing supply current to 0.01µA. Connect

SHDNA or SHDNB to a logic high or IN_ for always-on

operation of the corresponding LDO. Each LDO output

is internally discharged to ground through a 385Ω

resistor in shutdown mode.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX8559. Each regulator has its own inde-

pendent thermal detector. When one of the regulators’

lator’s pass transistor is turned off allowing the IC to

cool. The thermal sensor turns the pass transistor on

again after the IC’s junction temperature cools by 10°C.

This results in a pulsed output during continuous ther-

mal-overload conditions.

Operating Region and Power Dissipation

The MAX8559 maximum power dissipation depends on

the thermal resistance of the case and the circuit board,

the temperature difference between the die junction and

ambient air, and the rate of airflow. The power dissipa-

The maximum power dissipation allowed is:

the MAX8559 die junction and the surrounding air,

circuit board, copper traces, and other materials to the

surrounding air.

The exposed paddle of the TDFN package performs

the function of channeling heat away. Connect the

exposed paddle to the board ground plane.

Applications Information

Capacitor Selection and

Regulator Stability

For load currents up to 150mA, use a single 2.2µF

capacitor to bypass both inputs of the MAX8559 and a

2.2µF capacitor to bypass each output. Larger input-

capacitor values and lower ESRs provide better supply-

noise rejection and line-transient response. To reduce

output noise and improve load-transient voltage dips,

use larger output capacitors up to 10µF. For stable oper-

ation over the full temperature range with load currents

up to 300mA, input and output capacitors should be a

minimum of 4.7µF.

Note that some ceramic dielectrics exhibit large capaci-

tance and ESR variation with temperature. With

dielectrics such as Z5U and Y5V, it may be necessary to

use 4.7µF or more for up to 150mA load current to

ensure stability at temperatures below -10°C. With X7R

or X5R dielectrics, 2.2µF is sufficient at all operating tem-

peratures. These regulators are optimized for ceramic

capacitors. Tantalum capacitors are not recommended.

Use a 0.01µF bypass capacitor at BP for low-output volt-

age noise. Increasing the capacitance slightly decreas-

es the output noise, but increases the startup time.

PSRR and Operation from Sources Other

than Batteries

The MAX8559 is designed to deliver low-dropout volt-

ages and low quiescent currents in battery-powered

systems. Power-supply rejection ratio is 70dB at 10kHz

(see Power-Supply Rejection Ratio vs. Frequency in

the Typical Operating Characteristics). When operat-

ing from sources other than batteries, improved sup-

ply-noise rejection and transient response is achieved

by increasing the values of the input and output

bypass capacitors and through passive RC or CRC fil-

tering techniques.

Dual, 300mA, Low-Noise Linear Regulator

with Independent Shutdown in UCSP or TDFN

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