AME, Inc.
AME8861
600mA CMOS LDO
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General Description
The AME8861 family of positive, linear regulators fea-
ture low quiescent current (30µA typ.) with low dropout
voltage, making them ideal for battery applications. The
space-saving SOT-25 package is attractive 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.
In applications requiring a low noise, regulated supply,
place a 1000 pF capacitor between Bypass and ground.
The AME8861 is stable with an output capacitance of
2.2µF or greater.
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Functional Block Diagram
IN
OUT
Overcurrent
Shutdown
Thermal
Shutdown
EN
BYP
AMP
R1
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Features
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Very Low Dropout Voltage
600mA Output
Accurate to within 1.5%
30µA Quiescent Current
Over-Temperature Shutdown
Current Limiting
Short Circuit Current Fold-back
Noise Reduction Bypass Capacitor
Power-Saving Shutdown Mode
V
ref
=1.215V
R2
GND
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Typical Application
INPUT
IN
OUT
OUTPUT
AME8861
BYP
GND
EN
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Space-Saving SOT-25 Package
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Factory Pre-set Output Voltages
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Low Temperature Coefficient
C1
5V
1µF
µ
C2
1000pF
C3
2.2µF
µ
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Applications
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Instrumentation
Portable Electronics
Wireless Devices
Cordless Phones
PC Peripherals
Battery Powered Widgets
Electronic Scales
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AME, Inc.
AME8861
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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Detailed Description
The AME8861 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 AME8861 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8861 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.
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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 AME8861 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.
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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