AME, Inc.
AME8806 / 8809 / 8842
n Detailed Description
600mA CMOS LDO
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.
The AME8806/8809/8842 family of CMOS regulators
contain a PMOS pass transistor, voltage reference, error
amplifier, over-current protection, and thermal shutdown.
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 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.
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 AME8806/8809/8842 switches from voltage mode
to current mode when the load exceeds the rated output
current. This prevents over-stress. The AME8806/8809/
8842 also incorporates current foldback to reduce power
dissipation when the output is short circuited. This fea-
ture 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.
n External Capacitors
The AME8806/8809/8842 is stable with an output ca-
pacitor to ground of 2.2mF or greater. Ceramic capacitors
have the lowest ESR, and will offer the best AC perfor-
mance. Conversely, Aluminum Electrolytic capacitors
exhibit the highest ESR, resulting in the poorest AC re-
sponse. Unfortunately, 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.
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 ~
0.01mF. 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.
13
AME [ ANALOG MICROELECTRONICS ]
