Ultra-Low-Noise, High PSRR, Low-Dropout,

150mA Linear Regulators in µDFN

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For design purposes, consider the current limit to be

150mA (min) to 300mA (max). The output can be shorted

to ground for an indefinite amount of time without dam-

aging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipation

in the MAX8840/MAX8841/MAX8842. When the junction

signals the shutdown logic, turning off the pass transistor

and allowing the IC to cool down. The thermal sensor

turns the pass transistor on again after the IC’s junction

temperature drops by 10°C, resulting in a pulsed output

during continuous thermal-overload conditions.

Thermal-overload protection is designed to protect the

MAX8840/MAX8841/MAX8842 in the event of a fault

condition. For continual operation, do not exceed the

+150°C.

Operating Region and Power Dissipation

The MAX8840/MAX8841/MAX8842 maximum power

dissipation depends on the thermal resistance of the

case and circuit board, the temperature difference

between the die junction and ambient, and the rate of

airflow. The power dissipation across the device is:

The maximum power dissipation is:

the MAX8840/MAX8841/MAX8842 die junction and the

surrounding air,

package, and

PC board, copper traces, and other materials to the

surrounding air.

The GND pin of the MAX8840/MAX8841/MAX8842 per-

forms the dual function of providing an electrical con-

nection to ground and channeling heat away. Connect

the GND pin to ground using a large pad or ground

plane.

Noise Reduction

For the MAX8840, an external 0.01µF bypass capacitor

between BP and OUT with an innovative noise bypass

scheme reduces output noises dramatically, exhibiting

on circuit that precharges the bypass capacitor.

Applications Information

Capacitor Selection

and Regulator Stability

Use a 1µF capacitor on the MAX8840/MAX8841/

MAX8842 input and a 1µF capacitor on the output.

Larger input capacitor values and lower ESRs provide

better noise rejection and line-transient response.

Reduce output noise and improve load-transient

response, stability, and power-supply rejection by

using large output capacitors. Note that some ceramic

dielectrics exhibit large capacitance and ESR variation

with temperature. With dielectrics such as Z5U and

Y5V, it may be necessary to use a 2.2µF or larger output

capacitor to ensure stability at temperatures below

-10°C. With X7R or X5R dielectrics, 1µF is sufficient at all

operating temperatures. A graph of the Region of Stable

Operating Characteristics.

Use a 0.01µF bypass capacitor at BP (MAX8840) for

low-output voltage noise. The leakage current going into

the BP pin should be less than 10nA. Increasing the

capacitance slightly decreases the output noise. Values

above 0.1µF and below 0.001µF are not recommended.

Noise, PSRR, and Transient Response

The MAX8840/MAX8841/MAX8842 are designed to

deliver ultra-low noise and high PSRR, as well as low

dropout and low quiescent currents in battery-powered

systems. The MAX8840 power-supply rejection is 78dB

at 1kHz and 54dB at 100kHz. The MAX8841/MAX8842

PSRR is 72dB at 1kHz and 46dB at 100kHz (see the

Power-Supply Rejection Ratio vs. Frequency graph in

the Typical Operating Characteristics).

When operating from sources other than batteries,

improved supply-noise rejection and transient response

can be achieved by increasing the values of the input

and output bypass capacitors, and through passive fil-

tering techniques. The Typical Operating Characteristics

show the MAX8840/MAX8841/MAX8842 line- and load-

transient responses.

Dropout Voltage

A regulator’s minimum dropout voltage determines the

lowest usable supply voltage. In battery-powered sys-

tems, this determines the useful end-of-life battery volt-

age. Because the MAX8840/MAX8841/MAX8842 use a

p-channel MOSFET pass transistor, their dropout voltage

multiplied by the load current (see the Typical Ope-

rating Characteristics).