AME, Inc.
600mA CMOS LDO
AME8863
n Detailed Description
n Enable
The AME8863 family of CMOS regulators contain a
PMOS pass transistor, voltage reference, error amplifier,
over-current protection, thermal shutdown, and power
good function.
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 1mA. This pin behaves much
like an electronic switch.
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 150oC, or
the current exceeds 600mA. During thermal shutdown,
the output voltage remains low. Normal operation is re-
stored when the junction temperature drops below 120oC.
n Power Good
The AME8863 includes the Power Good feature. When
the output is not within +10% 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.
The AME8863 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8863 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 0.8volts, and reduces
the current flow by 65%. Full current is restored when
the voltage exceeds 0.8 volts.
(Note: PG pin is an open-drain output.)
n External Capacitors
The AME8863 is stable with an output capacitor to
ground of 2.2mF 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 0.1mF ceramic
capacitor with a 10mF 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 0.1mF 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.
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AKM [ ASAHI KASEI MICROSYSTEMS ]
