AME8807 Datasheet, PDF (5/11 Pages) Analog Microelectronics – 600mA CMOS LDO

Analog Microelectronics, Inc.
AME8807
600mA CMOS LDO
n Detailed Description
The AME8807 family of CMOS regulators contain a
PMOS pass transistor, voltage reference, error ampli-
fier, 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^oC, or the current exceeds 600mA. During thermal
shutdown, the output voltage remains low. Normal op-
eration is restored when the junction temperature drops
below 120^oC.
The AME8807 switches from voltage mode to current
mode when the load exceeds the rated output current.
This prevents over-stress. The AME8807 also incor-
porates current foldback to reduce power dissipation
when the output is short circuited. This feature becomes
active when the output drops below 0.8 volts, and re-
duces the current flow by 65%. Full current is restored
when the voltage exceeds 0.8 volts.
n 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.
n ADJ
The ADJ pin is the positive input to the error amplifier
which, due to the pmos pass element inversion, means
it is actually the negative input of the LDO feedback loop.
The feedback works to keep the voltage at the ADJ pin
1.215V with respect to ground. Since the internal cir-
cuitry at the ADJ pin is essentially an ESD protected
CMOS gate the input current at the ADJ pin is virtually
zero.
n External Capacitors
The AME8807 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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