AAT3258ITS-2.8-R-T1 datasheet(13/16 Pages) AAT

13 / 16 page

When the LDO regulator is in the shutdown mode,

an internal 1.5k

Ω resistor is connected between

OUT and GND. This is intended to discharge COUT

when the LDO regulator is disabled. The internal

1.5k

Ω has no adverse effect on device turn-on time.

Short-Circuit Protection

The LDO regulator section contains an internal

short-circuit protection circuit that will trigger when

the output load current exceeds the internal

threshold limit. Under short-circuit conditions, the

output of the LDO regulator will be current limited

until the short-circuit condition is removed from the

output or the LDO regulator package power dissi-

pation exceeds the device thermal limit.

Thermal Protection

The AAT3258 has an internal thermal protection cir-

cuit which will turn on when the device die temper-

ature exceeds 145°C. The internal thermal protec-

tion circuit will actively turn off the LDO regulator

output pass device to prevent the possibility of over-

temperature damage.

The LDO regulator output

will remain in a shutdown state until the internal die

temperature falls back below the 145°C trip point.

The combination and interaction between the short-

circuit and thermal protection systems allows the

LDO regulator to withstand indefinite short-circuit

conditions without sustaining permanent damage.

No-Load Stability

The LDO regulator is designed to maintain output

voltage regulation and stability under operational

no-load conditions. This is an important character-

istic for applications where the output current may

drop to zero.

Reverse Output-to-Input Voltage

Conditions and Protection

Under normal operating conditions, a parasitic diode

exists between the output and input of the LDO reg-

ulator.

The input voltage should always remain

greater than the output load voltage, maintaining a

reverse bias on the internal parasitic diode.

Conditions where V

OUT might exceed VIN should be

avoided since this would forward bias the internal

parasitic diode and allow excessive current flow into

the V

OUT pin, possibly damaging the LDO regulator.

In applications where there is a possibility of V

OUT

exceeding V

IN for brief amounts of time during nor-

mal operation, the use of a larger value C

IN capaci-

tor is highly recommended. A larger value of C

with respect to C

OUT will effect a slower CIN decay

rate during shutdown, thus preventing V

OUT from

exceeding V

IN.

In applications where there is a

greater danger of V

OUT exceeding VIN for extended

periods of time, it is recommended to place a

Schottky diode across V

IN to VOUT (connecting the

cathode to V

IN and anode to VOUT).

The Schottky

diode forward voltage should be less than 0.45V.

MicroPower Supervisory Circuit

Applications

Reset Output Options

The reset pin is an active low push-pull output. In

the event of a power down or brown-out condition,

the reset signal remains valid until the V

DET drops

below 1.2V.

Manual Reset Input

A logic low signal on MR asserts a reset condition.

Reset continues to be asserted as long as MR is low

and for a minimum of 150ms after MR returns high.

This input is internally pulled up to V

CC via a 20kΩ

resistor, so leaving the pin unconnected is accept-

able if a manual reset function is not needed. The

MR input is internally debounced, which allows use

of a mechanical switch. It should be a normally-

open momentary switch connected from MR to

GND. Additionally, the MR pin can be driven from

TTL, CMOS, or open drain logic outputs.

Supply Voltage Transient Behavior

In some cases, fast negative transients of short

duration can appear on the V

CC power supply. The

AAT3258 series device provides some immunity to

line transients which can generate invalid reset

AAT3258

300mA LDO Linear Regulator with µP Reset

3258.2006.03.1.6

AAT3258ITS-2.8-R-T1 Datasheet(PDF) 13 Page - Advanced Analog Technology, Inc.

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