AME8861_08 Datasheet, PDF (7/13 Pages) Analog Microelectronics – 600mA CMOS LDO

AME
AME8861
600mA CMOS LDO
n Detailed Description
The AME8861 family of CMOS regulators contain a
PMOS pass transistor, voltage reference, error amplifier,
over-current protection, and thermal shutdown.
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.
n Enable
The P-channel pass transistor receives data from the
error amplifier, over-current shutdown, and thermal pro-
tection circuits. During normal operation, the error ampli-
fier compares the output voltage to a precision reference.
Over-current and Thermal shutdown circuits become ac-
tive when the junction temperature exceeds 150^oC, or
The Enable pin normally floats high. When actively,
pulled low, the PMOS pass transistor shuts off, and all
internal circuits are powered down. In this state, the qui-
escent current is less than 1µA. This pin behaves much
like an electronic switch.
the current exceeds 600mA. During thermal^ws^whu^wtd^.mow^icn^r,^ochip.com
the output voltage remains low. Normal operation is re-
stored when the junction temperature drops below 120^oC.
The AME8861 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8861 also incorpo-
rates current foldback to reduce power dissipation when
the output is short circuited. This feature becomes ac-
tive when the output drops below 0.8 volts, and reduces
the current flow by 65%. Full current is restored when
the voltage exceeds 0.8 volts.
n External Capacitors
The AME8861 is stable with an output capacitor to
ground of 2.2µF 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.
A third capacitor can be connected between the BY-
PASS pin and GND. This capacitor can be a low cost
Polyester Film variety between the value of 0.001 ~
0.01µF. A larger capacitor improves the AC ripple rejec-
tion, but also makes the output come up slowly. This
"Soft" turn-on is desirable in some applications to limit
turn-on surges.
Rev.E.05
7