AME8844 Datasheet, PDF (6/14 Pages) Analog Microelectronics – 750mA CMOS LDO

AME, Inc.
AME8844
n Detailed Description
The AME8844 family of CMOS regulators contain a
PMOS pass transistor, voltage reference, error amplifier,
over-current protection, and thermal shutdown.
The P-channel pass transistor receives data from the
error amplifier, over-current shutdown, and thermal pro-
tection circuits. During normal operation, the error am-
plifier compares the output voltage to a precision refer-
ence. Over-current and Thermal shutdown circuits be-
come active when the junction temperature exceeds
140^oC, or the current exceeds 2.2A. During thermal shut-
down, the output voltage remains low. Normal operation
is restored when the junction temperature drops below
120^oC.
The AME8844 behaves like a current source when the
load reaches 2.2A. However, if the load impedance drops
below 0.3 ohms, the current drops back to 600mA to
prevent excessive power dissipation. Normal operation
is restored when the load resistance exceeds 0.75 ohms.
n External Capacitors
The AME8844 is stable with an output capacitor to
ground of 4.7µF or greater. Ceramic capacitors have the
lowest ESR, and will offer the best AC performance. Con-
versely, Aluminum Electrolytic capacitors exhibit the high-
est ESR, resulting in the poorest AC response. Unfortu-
nately, large value ceramic capacitors are comparatively
expensive. One option is to parallel a 0.1µF ceramic
capacitor with a 10µF Aluminum Electrolytic. The benefit
is low ESR, high capacitance, and low overall cost.
A second capacitor is recommended between the in-
put and ground to stabilize Vin. The input capacitor should
be at least 0.1µF to have a beneficial effect.
All capacitors should be placed in close proximity to
the pins. A "Quiet" ground termination is desirable. This
can be achieved with a "Star" connection.
750mA CMOS LDO
n Enable
When EN pin is pulled low, the PMOS pass transistor
shuts off, and all internal circuits are powered down. In
this state, the quiescent current is less than 2µA. This
pin behaves much like an electronic switch.
100K Ohm resistor is necessary between V_EN source
and EN pin when V_EN is higher than V_IN.
(Note: There is no internal pull-up for EN pin.
It can not be floating)
n Adjustable Version
The adjustable version uses external feedback resis-
tors to generate an output voltage anywhere from 1.5V to
5.0V. Vadj is trimmed to 1.24V and VOUT is given by the
equation:
VOUT = Vadj ( 1 + R1 / R2 )
Feedback resistors R1 and R2 should be high enough
to keep quiescent current low, but increasing R1 + R2
will reduce stability. In general, R1 and R2 in the 10’s of
kΩ will produce adequate stability, given reasonable lay-
out precautions. To improve stability characteristics, keep
parasitics on the ADJ pin to a minimum, and lower R1
and R2 values.
n Power Good
The AME8844 includes the Power Good feature. When
the output is not within ±15% of the specified voltage, it
pulls low. This can occur under the following conditions:
1) Input Voltage too low.
2) During Over-Temperature.
3) During Over-Current.
4) If output is pulled up.
(Note: PG pin is an open-drain output.)
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