AME
AME8816
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Detailed Description
The AME8816 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 140
o
C, or
the current exceeds 2.2A. During thermal shutdown, the
output voltage remains low. Normal operation is restored
when the junction temperature drops below 120
o
C.
The AME8816 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 operation
is restored when the load resistance exceeds 0.75 ohms.
1.5A CMOS LDO
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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.
100Kohm resistor is necessary between V
EN
source
and EN pin when V
EN
is higher than V
IN
.
(Note: There is no internal pull-up for EN PIN.)
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Adjustable Version
The adjustable version uses external feedback resis-
tors to generate an output voltage anywhere from 1.5V to
5.0V. Vadj is trimmed to 1.242V and VOUT is given by
the equation:
VOUT = Vadj ( 1 + R1 / R2 )
Feedback resistors R1 and R2 should be high enough
to keep quiescent current low, but increasing R1 + R2
will reduce stability. In general, R1 and R2 in the 10’s of
kΩ will produce adequate stability, given reasonable lay-
out precautions. To improve stability characteristics, keep
parasitics on the ADJ pin to a minimum, and lower R1
and R2 values.
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External Capacitors
The AME8816 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. 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.
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.
10
Rev. H.04
AME [ ANALOG MICROELECTRONICS ]
