AME8817 Datasheet, PDF (5/10 Pages) Analog Microelectronics – 1.5A CMOS LDO

Analog Microelectronics, Inc.
AME8817
PRELIMINARY
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^oC, 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^oC.
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.
n 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.
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.
n 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.
n 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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