Shutdown

The MAX8530/MAX8531 have a single shutdown con-

trol input (SHDN). Drive SHDN low to shut down both

outputs, reducing supply current to 10nA. Connect

SHDN to a logic high, or IN, for normal operation.

Internal P-Channel Pass Transistor

The MAX8530/MAX8531 feature two 1

Ω P-channel

MOSFET pass transistors. A P-channel MOSFET pro-

vides several advantages over similar designs using

PNP pass transistors, including longer battery life. It

requires no base drive, substantially reducing quies-

cent current. PNP-based regulators waste considerable

current in dropout when the pass transistor saturates

and also use high base-drive currents under heavy

loads. The MAX8530/MAX8531 do not suffer these

problems and consume only 150µA of quiescent cur-

rent whether in dropout, light-load, or heavy-load appli-

cations (see the Typical Operating Characteristics).

Whereas a PNP-based regulator has 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 voltage at lighter loads.

Current Limit

The MAX8530/MAX8531 contain two independent cur-

rent limiters, one for each regulator, which monitor and

control the pass transistor’s gate voltage and limit the

output currents to 210mA and 165mA minimum. The

output can be shorted to ground for an indefinite time

without damaging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX8530/MAX8531. When the junction tem-

signals the shutdown logic, turning off the pass transistor

and allowing the IC to cool. The thermal sensor turns the

pass transistor on again after the IC’s junction tempera-

ture cools by 10°C, resulting in a pulsed output during

continuous thermal-overload conditions.

Thermal-overload protection is designed to protect the

MAX8530/MAX8531 in the event of fault conditions. For

continual operation, do not exceed the absolute maxi-

Operating Region and Power Dissipation

The MAX8530/MAX8531s’ maximum power dissipation

depends on the thermal resistance of the case and cir-

cuit board, the temperature difference between the die

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

MAX8530/MAX8531 die junction and the surrounding air,

board, copper traces, and other materials to the sur-

rounding air.

The GND pin of the MAX853_ETT__ (6-lead QFN) per-

forms the dual functions of providing an electrical con-

nection to the ground and channeling heat away.

Connect the GND pin and exposed pad to ground

using a large pad or ground plane.

Low-Noise Operation (MAX8531)

An external 0.01µF bypass capacitor at BP, in conjunc-

tion with an internal resistor, creates a lowpass filter

(see the Typical Application Circuit). The MAX8531

Spectral Density vs. Frequency graph in the Typical

Operating Characteristics).

Dual Low-Dropout Linear Regulators

_______________________________________________________________________________________

7

IN

OUT1

2.2

µF

2.2

µF

INPUT

2.5V TO 6.5V

1.5V TO 3.3V

AT 200mA

1.5V TO 3.3V

AT 150mA

1

µF

10nF

SHDN

OFF

ON

OUT2

GND

BP

MAX8531

MAX8531

Typical Appication Circuit