AME, Inc.
AME8833/8834
High PSRR, 150mA CMOS LDO
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Detailed Description
The AME8833/8834 family of CMOS regulators con-
tain a PMOS pass transistor, voltage reference, error am-
plifier, 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 150mA. During thermal shutdown,
the output voltage remains low. Normal operation is re-
stored when the junction temperature drops below 120
o
C.
The AME8833/8834 switches from voltage mode to cur-
rent mode when the load exceeds the rated output cur-
rent. This prevents over-stress. The AME8833/8834 also
incorporates current foldback to reduce power dissipa-
tion when the output is short circuited. This feature be-
comes active when the output drops below 0.8volts, and
reduces the current flow by 65%. Full current is restored
when the voltage exceeds 0.8 volts.
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Shutdown
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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Adjustable Version
AME8834 features a user-adjustable output through an
external feedback resister divider. To set the output of
AME8834 use the following equation:
V
OUT
=V
ADJ
(1+R1/R2)
V
ADJ
=1.225V, use 1% or better resistors
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External Capacitors
The AME8833/8834 is stable with an output capacitor
to ground of 0.22µF 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.
A second capacitor is recommended between the in-
put and ground to stabilize Vin. The input capacitor should
be at least 1µF to have a beneficial effect.
A larger capacitor improves the AC ripple rejection, 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.
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AME [ ANALOG MICROELECTRONICS ]
