logic low on MR asserts reset while the regulator is still

within tolerance.

Reset remains asserted while MR is low and for the

reset timeout period (100ms min) after MR returns high.

The MR input has an internal pullup of 20k

Ω (typ) to

OUT. This input can be driven with TTL/CMOS logic

levels or with open-drain/collector outputs. Connect a

normally open momentary switch from MR to GND to

create a manual reset function; external debounce cir-

cuitry is not required. If MR is driven from long cables

or the device is used in a noisy environment, connect a

0.1µF capacitor from MR to GND to provide additional

noise immunity.

Reverse Leakage Protection

An internal circuit monitors the input and output volt-

ages. When the output voltage is greater than the input

voltage, the internal pass transistor and parasitic

diodes turn off. OUT powers the device. There is no

leakage path from OUT to IN. Therefore, the output can

be powered from an auxiliary supply such as a backup

battery without any need for additional blocking diodes.

Current Limit

The MAX6329/MAX6349 include a current limiter that

monitors and controls the pass transistor’s gate voltage,

limiting the output current to 350mA (typ). The output can

be shorted to ground for an indefinite period without

damaging the part.

Thermal Overload Protection

the thermal sensor signals the shutdown logic, turning

off the pass transistor and allowing the IC to cool. The

thermal sensor will turn the pass transistor on again

after the IC’s junction temperature cools by 20°C,

resulting in a pulsed output during continuous thermal-

overload conditions. Thermal overload protection is

designed to protect the MAX6329/MAX6349 in the

event of fault conditions. For continuous operation, do

not exceed the absolute maximum junction temperature

Operating Region and Power Dissipation

The MAX6329/MAX6349s’ maximum power dissipation

depends on the thermal resistance of the case and cir-

cuit board, the temperature difference between the die

junction and the ambient air, and the rate of airflow.

The power dissipation across the device is:

The maximum power dissipation is:

die junction and the surrounding air,

thermal resistance of the package, and

mal resistance through the printed circuit board, copper

traces, and other materials to the surrounding air.

The MAX6329/MAX6349s’ ground pin (GND) performs

the dual function of providing an electrical connection

to the system ground and channeling heat away.

Connect GND to the system ground using a large pad

or ground plane.

Applications Information

Output Voltage Selection

The MAX6329/MAX6349 feature dual mode operation:

they operate in either a preset voltage mode or an

adjustable mode. In preset voltage mode, internal

feedback resistors set the MAX6329/MAX6349 to

+3.3V, +2.5V, or +1.8V (see Selector Guide). Select this

mode by connecting SET to ground. In adjustable

mode, select an output between 1.23V to 5.0V using

two external resistors connected as a voltage divider to

SET (Figure 1). The output voltage is set by the following

equation:

Choose R2

≥ 100kΩ to optimize power consumption,

accuracy, and high-frequency power-supply rejection.

the output can be set using fixed resistors instead of

variable resistors. In preset voltage mode, impedance

between SET and ground should be less than 50k

Ω.

150mA, SOT23, Low Dropout Linear Regulators

with Internal Microprocessor Reset Circuit

8

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