Analog Microelectronics, Inc.
AME8806 / 8809 / 8842
600mA CMOS LDO
n
Detailed Description
The AME8806/8809 family of CMOS regulators con-
tain a PMOS pass transistor, voltage reference, error
amplifier, over-current protection, and thermal shut-
down.
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
150
o
C, or the current exceeds 600mA. During thermal
shutdown, the output voltage remains low. Normal op-
eration is restored when the junction temperature drops
below 120
o
C.
The AME8806/8809 switches from voltage mode to cur-
rent mode when the load exceeds the rated output cur-
rent. This prevents over-stress. The AME8806/8809
also incorporates current foldback to reduce power dis-
sipation 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.
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 re-
jection, but also makes the output come up slowly. This
"Soft" turn-on is desirable in some applications to limit
turn-on surges.
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 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
quiescent current is less than 1µA. This pin behaves
much like an electronic switch.
n
External Capacitors
The AME8806/8809 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.
Conversely, Aluminum Electrolytic capacitors exhibit
the highest ESR, resulting in the poorest AC response.
Unfortunately, large value ceramic capacitors are com-
paratively 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 over-
all cost.
A second capacitor is recommended between the input
and ground to stabilize Vin. The input capacitor should
be at least 0.1µF to have a beneficial effect.
8
AME [ ANALOG MICROELECTRONICS ]
