Analog Microelectronics, Inc.
AME8817
ARY
ELIMIN
PR
1.5A CMOS LDO
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General Description
The AME8817 family of positive, linear regulators fea-
ture low quiescent current (35µA typ.) with low dropout
voltage, making them ideal for battery applications.
Output voltages are set at the factory and trimmed to
1.5% accuracy.
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 1000pF capacitor between Bypass and Ground.
An additional feature is a "Power Good" detector, which
pulls low when the output is out of regulation.
The AME8817 is stable with an output capacitance of
4.7µF or greater.
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Features
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Very Low Dropout Voltage
Guaranteed 1.5A Output
Accurate to within 1.5%
35µA Quiescent Current Typically
Over-Temperature Shutdown
Current Limiting
Short Circuit Current Fold-back
Noise Reduction Bypass Capacitor
Power Good Output
Power-Saving Shutdown Mode
Space-Saving DDPAK-7 Package
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Low Temperature Coefficien
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Applications
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Functional Block Diagram
IN
OUT
Instrumentation
Portable Electronics
Wireless Devices
PC Peripherals
Battery Powered Widgets
Overcurrent
Shutdown
Thermal
Shutdown
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Typical Application
R1
IN
BYP (or ADJ)
IN
BYP
GND
OUT
AME8817
AMP
EN
OUT
PG
EN
PG
C1
5V
C2
C3
1
µF
1nF
4.7
µF
1.24V
R2
GND
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Analog Microelectronics, Inc.
AME8817
ARY
ELIMIN
PR
1.5A CMOS LDO
n
Detailed Description
The AME8817 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 2.2A. During thermal shut-
down, the output voltage remains low. Normal operation
is restored when the junction temperature drops below
110
o
C.
The AME8817 behaves like a current source when the
load reaches 2.2A. However, if the load impedance
drops below 0.3 ohms, the current drops back to 600mA
to prevent excessive power dissipation. Normal op-
eration is restored when the load resistance exceeds
0.75 ohms.
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
When 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 AME8817 includes the Power Good feature. Nor-
mally, the PG pin is "Floating", however, when the out-
put is not within
±15%
of the specified voltage, it pulls
low. This can occur under the following conditions:
1) Input Voltage too low.
2) During Over-Temperature.
3) During Over-Current.
4) If output is pulled up.
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External Capacitors
The AME8817 is stable with an output capacitor to ground
of 4.7µF 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 comparatively expen-
sive. 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 input
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 re-
jection, 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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PCB Design
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