MAX15027 Datasheet, PDF(9/10 Page) Maxim Integrated Products – 1.425V to 3.6V Input, 1A Low-Dropout Regulators with BIAS Input

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MAX15027 Datasheet, PDF (9/10 Pages) Maxim Integrated Products – 1.425V to 3.6V Input, 1A Low-Dropout Regulators with BIAS Input

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1.425V to 3.6V Input, 1A Low-Dropout

Regulators with BIAS Input

Capacitor Selection and

Regulator Stability

Capacitors are required at the MAX15027/MAX15028âs

inputs and outputs for stable operation over the full

temperature range and with load currents up to 1A.

Connect a 1ÂµF capacitor between IN and ground and a

4.7ÂµF capacitor with low equivalent series resistance

(ESR) between OUT and ground for 1A output current.

The input capacitor (CIN) lowers the source impedance

of the input supply. If input supply source impedance is

high, place a larger input capacitor close to IN to pre-

vent VIN sagging due to load transients. Smaller output

capacitors can be used for output currents less than

1A. Calculate the minimum COUT as follows:

COUT

IOUT(MAX)

ââ

1ÂµF

0.25A

â â

Operating Region and

Power Dissipation

The maximum power dissipation depends on the ther-

mal resistance of the IC package and circuit board, the

temperature difference between the die junction and

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

ed in the device is PDISS = IOUT (VIN - VOUT). The

package features an exposed thermal pad on its

underside. This pad lowers the thermal resistance of

the package by providing a direct heat conduction

path from the die to the PCB. Connect the exposed

backside pad and GND to the system ground using a

large pad or ground plane and multiple vias to the

ground plane layer.

Noise, PSRR, and Transient Response

The MAX15027/MAX15028 are designed to operate

with low-dropout voltages and low quiescent currents

while still maintaining good noise performance, tran-

sient response, and AC rejection (see the Typical

Operating Characteristics for a plot of Power-Supply

Rejection Ratio (PSRR) vs. Frequency). When operating

from noisy sources, improved supply-noise rejection

and transient response can be achieved by increasing

the values of the input and output bypass capacitors

and through passive filtering techniques. The

MAX15027/MAX15028 load-transient response graphs

(see the Typical Operating Characteristics) show two

components of the output response: a DC shift from the

output impedance due to the load current change, and

the transient response. A typical transient overshoot for

a step change in the load current from 300mA to

800mA is 15mV. Use ceramic output capacitors greater

than 4.7ÂµF (up to 100ÂµF) to attenuate the overshoot.

Layout Guidelines

The TDFN package has an exposed thermal pad on its

underside. This pad provides a low thermal resistance

path for heat transfer into the PCB. This low thermally

resistive path carries a majority of the heat away from

the IC. The PCB is effectively a heatsink for the IC. The

exposed pad should be connected to a large ground

plane for proper thermal and electrical performance.

The minimum size of the ground plane is dependent

upon many system variables. To create an efficient

path, the exposed pad should be soldered to a thermal

landing, which is connected to the ground plane by

thermal vias. The thermal landing should be at least as

large as the exposed pad.

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