Analog Microelectronics, Inc.
1
AME8808
750mA CMOS LDO
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Typical Application
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Functional Block Diagram
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Features
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Very Low Dropout Voltage
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Guaranteed 750mA Output
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Accurate to within 1.5%
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30
µ
A Quiescent Current
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Over-Temperature Shutdown
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Current Limiting
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Short Circuit Current Fold-back
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Space-Saving SOT-223 and DPAK-2 Package
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Factory Pre-set Output Voltages
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Low Temperature Coefficient
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General Description
The AME8808 family of positive, linear regulators feature
low quiescent current (30
µ
A typ.) with low dropout volt-
age, making them ideal for battery applications. The
space-saving SOT-223 and DPAK-2 packages are attrac-
tive for "Pocket" and "Hand Held" applications.
These rugged devices have both Thermal Shutdown,
and Current Fold-back to prevent device failure under
the "Worst" of operating conditions.
The AME8808 is stable with an output capacitance of
2.2
µ
F or greater.
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Applications
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Instrumentation
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Portable Electronics
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Wireless Devices
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Cordless Phones
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PC Peripherals
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Battery Powered Widgets
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Electronic Scales
AME8808
O U T
IN
C 2
2.2
µ
F
C 1
1
µ
F
IN
G N D
O U T
5 V
Overcurrent
Shutdown
Thermal
Shutdown
A M P
G N D
O U T
IN
R 1
R 2
V
ref
= 1 . 2 1 5 V
Analog Microelectronics, Inc.
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750mA CMOS LDO
AME8808
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Detailed Description
The AME8808 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 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 750mA. During thermal
shutdown, the output voltage remains low. Normal op-
eration is restored when the junction temperature drops
below 120
o
C.
The AME8808 switches from voltage mode to current mode
when the load exceeds the rated output current. This
prevents over-stress. The AME8808 also incorporates
current foldback to reduce power dissipation 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.
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External Capacitors
The AME8806/8809 is stable with an output capacitor
to ground of 2.2
µ
F 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 0.1
µ
F
ceramic capacitor with a 10
µ
F 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 0.1
µ
F 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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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 1
µ
A. This pin behaves
much like an electronic switch.
