AAT3258_06 Datasheet, PDF (13/16 Pages) Advanced Analogic Technologies – 300mA LDO Linear Regulator with μP Reset

AAT3258
300mA LDO Linear Regulator with µP Reset
When the LDO regulator is in the shutdown mode,
an internal 1.5kΩ resistor is connected between
V_OUT and GND. This is intended to discharge C_OUT
when the LDO regulator is disabled. The internal
1.5kΩ 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 V_IN 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_IN
with respect to C_OUT will effect a slower C_IN decay
rate during shutdown, thus preventing V_OUT from
exceeding V_IN. In applications where there is a
greater danger of V_OUT exceeding V_IN for extended
periods of time, it is recommended to place a
Schottky diode across V_IN to V_OUT (connecting the
cathode to V_IN and anode to V_OUT). 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
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