AME, Inc.
AME8807
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Detailed Description
The AME8807 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 AME8807 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8807 also incorpo-
rates current foldback to reduce power dissipation when
the output is short circuited. This feature becomes ac-
tive 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
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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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ADJ
The ADJ pin is the positive input to the error amplifier
which, due to the pmos pass element inversion, means it
is actually the negative input of the LDO feedback loop.
The feedback works to keep the voltage at the ADJ pin
1.215V with respect to ground. Since the internal cir-
cuitry at the ADJ pin is essentially an ESD protected
CMOS gate the input current at the ADJ pin is virtually
zero.
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External Capacitors
The AME8807 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
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.
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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