AME, Inc.
AME8806 / 8809 / 8842
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Detailed Description
The AME8806/8809/8842 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 150
o
C, or
the current exceeds 600mA. During thermal shutdown,
the output voltage remains low. Normal operation is re-
stored when the junction temperature drops below 120
o
C.
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.
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.
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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 qui-
escent current is less than 1µA. This pin behaves much
like an electronic switch.
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External Capacitors
The AME8806/8809/8842 is stable with an output ca-
pacitor to ground of 2.2µF 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 0.1µF
ceramic capacitor 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.
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 rejec-
tion, but also makes the output come up slowly. This
"Soft" turn-on is desirable in some applications to limit
turn-on surges.
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AME [ ANALOG MICROELECTRONICS ]
