AME8847 Datasheet, PDF (6/12 Pages) Analog Microelectronics – 800mA CMOS LDO

AME, Inc.
AME8847
n Detailed Description
The AME8847 of CMOS regulators contains 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 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 current exceeds 900mA. During thermal shutdown,
the output voltage remains low. Normal operation is re-
stored when the junction temperature drops below 120^oC.
The AME8847 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8847 also incorpo-
rates current foldback to reduce power dissipation when
the output is short circuited. This feature becomes active
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.
800mA CMOS LDO
n External Capacitors
The AME8847 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 ca-
pacitor 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.
6
Rev.A.01