Low-Noise, Low-Dropout,

150mA Linear Regulators in SOT23

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7

An external bypass capacitor connected to the BP pin

reduces noise at the output. Additional blocks include a

current limiter, reverse battery protection, thermal sen-

sor, and shutdown logic. The MAX8868 also includes

an auto-discharge function, which actively discharges

the output voltage to ground when the device is placed

in shutdown mode.

Output Voltage

The MAX8867/MAX8868 are supplied with factory-set

output voltages from 2.5V to 5V, in 100mV increments.

Except for the MAX886_EUK29 and the MAX886_EUK32

(which have an output voltage preset at 2.84V and

3.15V, respectively), the two-digit suffix allows the cus-

tomer to choose the output voltage in 100mV increments.

For example, the MAX8867EUK33 has a preset output

voltage of 3.3V. (see

Expanded Ordering Information).

Internal P-Channel Pass Transistor

The MAX8867/MAX8868 feature a 1.1

Ω typical P-chan-

nel MOSFET pass transistor. This provides several

advantages over similar designs using PNP pass tran-

sistors, including longer battery life. The P-channel

MOSFET requires no base drive, which reduces quies-

cent current considerably. PNP-based regulators waste

considerable current in dropout when the pass transis-

tor saturates. They also use high base-drive currents

under large loads. The MAX8867/MAX8868 do not suf-

fer from these problems and consume only 100µA of

quiescent current whether in dropout, light-load, or

heavy-load applications (see the

Typical Operating

Characteristics).

Current Limit

The MAX8867/MAX8868 include a current limiter, which

monitors and controls the pass transistor’s gate voltage,

limiting the output current to 390mA. For design purposes,

consider the current limit to be 160mA minimum to 500mA

maximum. The output can be shorted to ground for an

indefinite amount of time without damaging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX8867/MAX8868. When the junction tem-

signals the shutdown logic, turning off the pass transis-

tor 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

MAX8867/MAX8868 in the event of fault conditions. For

continual operation, do not exceed the absolute maxi-

Operating Region and Power Dissipation

The MAX8867/MAX8868’s 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 air flow. The

MAX8867/MAX8868 die junction and the surrounding

air,

age, and

printed circuit board, copper traces, and other materi-

als to the surrounding air.

The GND pin of the MAX8867/MAX8868 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 MAX8867/MAX8868 have a unique protection

scheme that limits the reverse supply current to 1mA

cuitry monitors the polarity of these two pins and dis-

connects the internal circuitry and parasitic diodes

when the battery is reversed. This feature prevents

device damage.

Noise Reduction

An external 0.01µF bypass capacitor at BP, in conjunction

with an internal 200k

Ω resistor, creates a 80Hz lowpass

filter for noise reduction. The MAX8867/MAX8868 exhibit

power-on circuit that pre-charges the bypass capacitor.

The

Typical Operating Characteristics show graphs of

Noise vs. BP Capacitance, Noise vs. Load Current, and

Output Noise Spectral Density.

__________Applications Information

Capacitor Selection and

Regulator Stability

Normally, use a 1µF capacitor on the MAX8867/

MAX8868’s input and a 1µF to 10µF capacitor on the

output. Larger input capacitor values and lower ESRs

provide better supply-noise rejection and line-transient

response. Reduce noise and improve load-transient

response, stability, and power-supply rejection by

using large output capacitors. For stable operation over

the full temperature range and with load currents up to

150mA, a minimum of 1µF is recommended. Note that

some ceramic dielectrics exhibit large capacitance and