Product Brief
AS1124 Product Brief Page 1
AS1124
24W Powered Device
with Integrated DC-DC Conversion
General Description
The AS1124 is a single-chip, highly integrated CMOS
solution for Power over Ethernet (PoE). Applications
include Voice over IP (VoIP) Phones, Wireless LAN Access
Point, Security and Web Cameras, Analog Telephone
Adapters (ATA) and Point of Sale s Terminals.
The AS1124 provides the functions required for power over
Ethernet PD applications .
By using high-volume standard CMOS technology, Akros
enables its customers to bring to market higher
performance PoE devices with low cost and a small
footprint.
The AS1124 integrates rectification and protection circuitry,
a PD controller, and a DC-DC converter. This high level of
integration provides faster ressponse to surge events and
limits stray surge current from passing through sensitive
circuits, such as the Ethernet PHY device. The device is
designed to provide a safe low impedance discharge paths
directly back to the earth ground, resulting in superior reliability
and circuit protection.
The AS1124 also supports higher power requirements. The
device provides an extended classification scheme that
allows for higher classes as power requirements cross
above IEEE® Std. 802.3a f -2003 limits.
Features
The AS1124 is fully integrated and architected at a
system level to provide the following features:
• Fully supports IEEE® Std. 802.3af-2003 and
supports pre-standard IEEE® Std. 802.3at-2006
power requirements
• Meets IEC 61000-4-2/3/4/5/6 requirements for
electric discharge
• Meets IEC 60950 overvoltage protection
• Integrated rectification and cable discharge
protection
• Integrated DC-DC converter provides exceptional EMI
performance
• Programmable DC current limit up to 800 mA
• Supports “two finger” classification for pre-standard
IEEE® Std. 802.3at-2006 higher power PD applications
• Provides seamless support for local power
• Over temperature protection
• 5x5 mm QFN Package, RoHS Compliant
Typical Applications
• Voice over IP (VoIP) phones
• Wirele ss LA N Ac ce ss Points
• Pan, Tilt and Zoom, security and Web Cameras
• Analog Telephone Adapters (ATA)
• Point of Sale (PoS) Termin al
Example Application Diagram
Figure 1: Typical Application Diagram for Gigabit Ethernet based PD (Flyback converter)
AS1124
Product Brief
AS1124 Product Brief Page 2
Figure 1: Top-Level Block Diagram of the AS1124
Description
The AS1124 is a fully integrated PD that provides functions
required for Power over Ethernet (PoE) applications and is
scalable to support higher power applications over 2 pairs of
CAT5e/6 cables. The optimized architecture of the AS1124
reduces external component cost in a small footprint
package while providing high performance. The AS1124
provides:
PD Control
The AS1124 PD Control interface is designed to provide a
fully compliant IEEE 802.3af and higher powered PD
system, with programmable support for the standard PD
control functions.The PD Control provides the following
major func tions:
•Signals that it is a PD
•Determines the mode of operation of the AS1124,
based on the IEEE 802 .3af standard.
•Determines the mode of operation of the AS1124,
based on the extended classification for higher
power option.
•Manages power and thermal protection overrides.
Modes of Operation
The AS1124 has four mode s of operation:
1. Signature Detection - The PD signature is detected
by the AS1124 to allow classification.
2. Classification - The PD signature is classified, to
determine the power requirements of the PD.
3. Normal Operation - The PD is supplied the proper
power by the AS1124.
4. Disable - PSE voltage is below normal and the
power to the PD is off.
As the supply voltage from the PSE increases from initial 0V,
the part transitions through the modes of operation in this
sequence:
If no PSE is present, the AS1124 remains in the disable
mode and does not affect the Ethernet link.
PD Control Power and Thermal Protections
The AS1124 provides the following features for PD Control
Power and Thermal protection:
Under Voltage Lockout (UVLO)—The UVLO
circuitry detects conditions when the voltage is
too low, and disconnects the power to protect the
PD.
•Current Limit/Current Sense—senses the
operating current via the sense resistor and
regulates the gate voltage on the on-chip power
MOSFET to minimize on-chip Po wer dissipation.
•Thermal Limit/Protection— the AS1124
provides thermal protection for the IC by monitoring
die temperatures and reducing current, or
disconnecting power as appropriate.
DC-DC Conversion
The integrated DC-DC converter operates from a switched
input voltage and includes soft-start and current limiting.
After the input power and enable signals are asserted, the
DC-DC controller starts up. The converter provides control
signals to external MOSFET switches and uses an external
sense resistor to sense the tran sfo rmer primary current.
As part of full system level solution for EMI, Akros has
focused significant effort in reducing switching noise in the
integrated power converters through unique techniques of
balancing the signaling of the FET drivers and reducing
ground bounce by minimizing the dV/dt switching noise.
The DC-DC architecture is a current mode converter which
can be configured with external component changes for
either flyback, forward or buck topologies. Both non-isolated
and isolated switching technologies are supported. The
PWM switching signal is controlled for low radiated and
conducted emissions.
For More Information
Contact us at marcom@akrossilicon.c om, or Akros Silicon,
Disable Signature Detection Classification Normal Operation
6399 San Ignacio Ave, Suite 250, San Jose, CA 95119
