AAT3258
300mA LDO Linear Regulator with µP Reset
When the LDO regulator is in the shutdown mode,
avoided since this would forward bias the internal
parasitic diode and allow excessive current flow into
the VOUT pin, possibly damaging the LDO regulator.
an internal 1.5kΩ resistor is connected between
VOUT and GND. This is intended to discharge COUT
when the LDO regulator is disabled. The internal
1.5kΩ has no adverse effect on device turn-on time.
In applications where there is a possibility of VOUT
exceeding VIN for brief amounts of time during nor-
mal operation, the use of a larger value CIN capaci-
tor is highly recommended. A larger value of CIN
with respect to COUT will effect a slower CIN decay
rate during shutdown, thus preventing VOUT from
exceeding VIN. In applications where there is a
greater danger of VOUT exceeding VIN for extended
periods of time, it is recommended to place a
Schottky diode across VIN to VOUT (connecting the
cathode to VIN and anode to VOUT). The Schottky
diode forward voltage should be less than 0.45V.
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.
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 VDET drops
below 1.2V.
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.
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 VCC 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.
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 VOUT might exceed VIN should be
Supply Voltage Transient Behavior
In some cases, fast negative transients of short
duration can appear on the VCC power supply. The
AAT3258 series device provides some immunity to
line transients which can generate invalid reset
3258.2006.03.1.6
13
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
