AIC1531
7
n BLOCK DIAGRAM
n PIN DESCRIPTION
PIN 1:
VSBY - Standby supply voltage (5V) input
for 3.3V regulator when VCC falls
below VCCDES. Some NICs that
operate in “ Wake-On-LAN” mode
get a 5V standby through a cable
that connects directly to a specific
header on the Motherboard.
PIN 2:
VCC
- Primary supply voltage (5V) input
for 3.3V regulator.
PIN 3:
VOUT - 3.3V
regulated
output
voltage
when either VCC or VSBY is present.
When only VAUX (3.3V) is present,
VOUT voltage comes from VAUX
through an internal low impedance
switch.
PIN 4:
AUX
- Auxiliary supply voltage (3.3V)
input for low impedance switch.
PIN 5-8: GND
- Negative reference for all voltages.
n APPLICATIONS INFORMATION
The Requirement for External Capacitors
The selection of the output capacitor is based on
two requirements: LDO compensation and the
transition between power sources. During the
takeover between sources, the output capacitor
provides the loading. Therefore a larger output
capacitor can improve the transition. And since the
output capacitor plays the important role in the
compensation of LDO, a 10
µF Tantalum capacitor
or larger is recommended.
The input capacitor is required to be as close to the
IC as possible. The input capacitor can reduce the
parasitic effect formed by the power supply output
impedance or the trace. A 10
µF Tantalum capacitor
is a good choice. Additional ceramic capacitor can
be placed close to input and output to reduce the
high frequency noise. A 0.1
µF is recommended.
The layout and Thermal Considerations
The AIC1531 is housed in a thermally enhanced
package where the GND pins (Pin5 to Pin8) are
integrated to the leadframe. Generally, heat sinks
are not available for most surface-mounted devices.
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