AME8845_11 Datasheet, PDF (11/19 Pages) Analog Microelectronics – 3A CMOS LDO

AME
AME8845
n Detailed Description
The AME8845 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 ampli-
fier compares the output voltage to a precision reference.
Over-current and Thermal shutdown circuits become ac-
tive when the junction temperature exceeds 140^oC, or
the current exceeds 4.5A. During thermal shutdown, the
output voltage remains low. Normal operation is restored
when the junction temperature drops below 110^oC.
The AME8845 behaves like a current source when the
load reaches 4.5A. 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 AME8845 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.
Rev.C.03
3A CMOS LDO
11