AAT3237 Datasheet, PDF (10/13 Pages) Advanced Analogic Technologies – 300mA MicroPower™ LDO with PowerOK

AAT3237
300mA MicroPower™ LDO with PowerOK
POK Output
The AAT3237 features an integrated Power-OK
comparator which can be used as an error flag. The
POK open-drain output goes low when OUT is 6%
below its nominal regulation voltage. Connect a
pull-up resistor from POK to OUT.
Enable Function
The AAT3237 features an LDO regulator enable/
disable function. This pin (EN) is active high and is
compatible with CMOS logic. To assure the LDO
regulator will switch on, the EN turn-on control level
must be greater than 2.0V. The LDO regulator will
go into the disable shutdown mode when the volt-
age on the EN pin falls below 0.6V. If the enable
function is not needed in a specific application, it
may be tied to V_IN to keep the LDO regulator in a
continuously on state.
When the LDO regulator is in 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 AAT3237 contains an internal short-circuit pro-
tection circuit that will trigger when the output load
current exceeds the internal threshold limit. Under
short-circuit conditions, the output of the LDO reg-
ulator will be current limited until the short-circuit
condition is removed from the output or LDO regu-
lator package power dissipation exceeds the
device thermal limit.
Thermal Protection
The AAT3237 has an internal thermal protection cir-
cuit which will turn on when the device die tempera-
ture exceeds 145°C. The internal thermal protection
circuit will actively turn off the LDO regulator output
pass device to prevent the possibility of over-temper-
ature 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 AAT3237 is designed to maintain output volt-
age regulation and stability under operational no-
load conditions. This is an important characteristic
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 regulator. The input voltage should always
remain greater than the output load voltage, main-
taining 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.
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3237.2006.01.1.4