Analog Microelectronics, Inc.
AME8804
300mA CMOS LDO
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General Description
The AME8804 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-26 and SOT-25 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 SOT-26 version also features a "Power Good" de-
tector, which pulls low when the output is out of regula-
tion.
The AME8804 is stable with an output capacitance of
2.2µF or greater.
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Features
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Very Low Dropout Voltage
Guaranteed 300mA Output
Accurate to within 1.5%
30µA Quiescent Current
Over-Temperature Shutdown
Current Limiting
Short Circuit Current Fold-back
Power Good Detector (6 pin version only)
Power-Saving Shutdown Mode
Space-Saving SOT-26 and SOT-25
Adjustable Output Voltages
Low Temperature Coefficient
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Applications
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Functional Block Diagram
IN
Overcurrent
Shutdown
OUT
Instrumentation
Portable Electronics
Wireless Devices
Cordless Phones
PC Peripherals
Battery Powered Widgets
Electronic Scales
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Typical Application
IN
C1
5V
AMP
ADJ
OUT
EN
IN
AME8804
PG
G N D ADJ
Thermal
Shutdown
OUT
C2
R1
100p
C3
2.2µF
R2
EN
V
ref
x110%
1µF
PG
V
ref
x90%
V
ref
=1.215V
GND
V
OUT
= 1.215 (R1 +R2)/R2
C2 is unnecessary when R1 or R2 < 20K
PG pin is only available in the SOT-26 package option
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Analog Microelectronics, Inc.
AME8804
300mA CMOS LDO
n
Detailed Description
The AME8804 family of CMOS regulators contain a
PMOS pass transistor, voltage reference, error ampli-
fier, over-current protection, thermal shutdown, and
Power Good detection circuitry.
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 300mA. During thermal
shutdown, the output voltage remains low. Normal op-
eration is restored when the junction temperature drops
below 120
o
C.
The AME8804 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8804 also incor-
porates current foldback to reduce power dissipation
when the output is short circuited. This feature becomes
active when the output drops below 0.8volts, and re-
duces 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
quiescent current is less than 1µA. This pin behaves
much like an electronic switch.
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Power Good
The AME8804 (SOT-26 package only) includes the Power
Good feature. Normally, Pin 4 is "Floating", however,
when the output is not within
±10%
of the specified volt-
age, it pulls low. This can occur under the following con-
ditions:
1)
2)
3)
4)
Input Voltage too low.
During Over-Temperature.
During Over-Current.
If output is pulled up.
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External Capacitors
The AME8804 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.
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 0.1µF
ceramic capacitor with a 10µF 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 0.1µF 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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