MAX15027ATBT データシートの表示（PDF） - Maxim Integrated

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MAX15027ATBT

1.425V to 3.6V Input, 1A Low-Dropout Regulators with BIAS Input

Maxim Integrated 

MAX15027/MAX15028

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

Regulators with BIAS Input

Detailed Description

The MAX15027/MAX15028 low-dropout linear regulators

operate from input voltages as low as 1.425V and deliver

up to 1A of continuous output current with a maximum

dropout voltage of only 225mV.

The MAX15028 operates with an input voltage as low

as 1.425V if the bias voltage (VBIAS) of 3V to 5.5V is

available. The power is applied at IN while the control is

provided through BIAS input. The current drawn by BIAS is

negligible when the LDO goes into shutdown. This feature

is especially useful in automotive applications where the

BIAS input is derived from an always-on LDO that expects

to provide minimal power during the key-off condition.

The pMOS output stage can be driven from input voltages

down to +1.425V without sacrificing stability or transient

performance. The output voltage of all the regulators is

adjustable from 0.5V to VIN and is ±2% accurate over

load and line variations, from -40°C to +125°C. Since

these regulators have a pMOS output device, supply

current is not a significant function of load or input head-

room.

Internal p-Channel Pass Transistor

The devices feature a 75mΩ (typ) p-channel MOSFET

pass transistor. Unlike similar designs using pnp pass

transistors, p-channel MOSFETs require no base drive,

reducing quiescent current.

pnp-based regulators also waste considerable current in

dropout when the pass transistor saturates and use high

base-drive currents under large loads. The devices do

not suffer from these problems and consume only 275μA

(typ) of quiescent current under heavy loads, as well as

in dropout.

Short-Circuit/Thermal Fault Protection

The devices are fully protected from a short circuit at

the output through current limiting and thermal-overload

circuitry. In the fault condition when the output is shorted

to ground, the output current is limited to a maximum of

2A. Under these conditions, the device quickly heats up.

When the junction temperature reaches +165°C (typ), the

thermal-overload circuitry turns off the output, allowing the

part to cool down. When the junction temperature cools to

+150°C (typ), the output turns back on and reestablishes

regulation. Current limiting and thermal protection contin-

ue until the fault is removed. For continuous operation, do

not exceed the absolute maximum junction-temperature

rating of TJ = +150°C.

Soft-Start

The devices feature a soft-start function that slowly ramps

up the output voltage of the regulator based on the value

of the capacitor (CSS) connected from SS to GND. Upon

power-up, CSS is charged with a 5μA (typ) current source

through SS. The voltage at SS is compared to the internal

0.5V reference (VREF). The feedback voltage for regula-

tion (VREG) is the lower of VSS or VREF. As VSS rises,

the regulation voltage (VREG) rises at the same rate.

Once VSS reaches and rises above VREF, the regulation

voltage then tracks the reference voltage since it is the

lower of VSS and VREF. The value of CSS determines the

length of the soft-start time, tSS. Use the following formula

to determine CSS.

CSS = 10-5 x tSS

where CSS is in farads and tSS is in seconds.

Shutdown Mode

The devices include an enable input. To shut down the

IC, drive EN low. In shutdown mode, the current drawn

by BIAS is less than 2μA. This feature is extremely use-

ful in an automotive application where the BIAS input

is derived from an always-on LDO expecting to provide

minimal dark current. For normal operation, drive EN high

or connect EN to IN (BIAS for MAX15028) for continuous

on operation. During shutdown, an internal 10kΩ resistor

is connected between OUT and GND.

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