ncp1083 ON Semiconductor, ncp1083 Datasheet - Page 11

• Manufacturer Part Number: ncp1083
• Description: Integrated High Power Poe-pd Interface & Dc-dc Converter Controller With 9v Auxiliary Supply Support
• Manufacturer: ON Semiconductor

IEEE 802.3af and draft IEEE 802.3at (D3.0) defined
operating modes: detection signature, current source
classification, inrush and operating current limits. In order
to give more flexibility to the user and also to keep control
of the power dissipation in the NCP1083, both current limits
are configurable. The device enters operation once its
programmable Vuvlo_on threshold is reached, and
operation ceases when the supplied voltage falls below the
Vuvlo_off threshold. Sufficient hysteresis and Uvlo filter
time are provided to avoid false power on/off cycles due to
transient voltage drops on the cable.
resistance seen by the PSE through the cable must be in the
IEEE 802.3af standard specification range (23.75 kW to
26.25 kW) for a PSE voltage from 2.7 V to 10.1 V. In order
to compensate for the non-linear effect of the diode bridge
and satisfy the specification at low PSE voltage, the
NCP1083 presents suitable impedance in parallel with the
25.5 kW Rdet external resistor. For some types of diodes
(especially Schottky diodes), it may be necessary to adjust
this external resistor.
11.5 V) on VPORTP, the NCP1083 turns on its internal
3.3 V regulator and biasing circuitry in anticipation of the
classification phase as the next step.
Classification
classification process begins. The NCP1083 is fully capable
of responding and completing all classification handshaking
procedures as described next.
Classification Current Source Generation
source that is set by the external resistor RCLASS value on
the CLASS pin. Figure 8 shows the schematic overview of
the classification block. The current source is defined as:
Powered Device Interface
Detection
The PD interface portion of the NCP1083 supports the
During the detection phase, the incremental equivalent
When the Detection_Off level is detected (typically
Once the PSE device has detected the PD device, the
In classification, the PD regulates a constant current
Rclass
VPORTN1,2
VPORTP
CLASS
Figure 8. Classification Block Diagram
I
class
+
R
V
class
bg
, (where V
VDDA1
bg
NCP1083
is 1.2 V)
1.2 V
Description of Operation
http://onsemi.com
11
classification, IEEE 802.3af, draft IEEE 802.3at (D3.0) and
proprietary classification.
performed with a Single Event Layer 1 classification.
Depending on the current level set during that single event
the power level is determined. The current draft IEEE
802.3at (D3.0) allows two ways of classification which can
also be combined. These two approaches enable higher
power applications through a variety of PSE equipment.
hardware handshake is introduced called Two Event Layer
1 classification. This approach allows equipment that has no
data link between PSE and PD to classify as high power.
PD, a software handshake is possible. This type of
handshake is called Layer 2 classification (or Data Link
Layer classification). It has the main advantage of having a
finer power resolution and the ability for the PSE and PD to
participate in dynamic power allocation.
One Event Layer 1 Classification
Event Layer 1 classification event by increasing the line
voltage into the classification range only once.
Two Event Layer 1 Classification
physical classification performs two classification events
and looks for the appropriate response from the PD to check
if the PD is draft IEEE 802.3at (D3.0) compatible.
During the first classification finger, the PSE will measure
the classification current which should be 40 mA if the PD
is at compliant. If this is the case, the PSE will exit the
classification range and will force the line voltage into the
Mark Event range. Within this range, the PSE may check the
non-valid input signature presented by the PD (using the two
point measurement defined in the IEEE 802.3af standard).
Then the PSE will repeat the same sequence with the second
classification finger. A PD which has detected the sequence
“Finger + Mark + Finger + Mark” knows the PSE is draft
IEEE 802.3at (D3.0) compliant, meaning the PSE will
deliver more current on the port. (Note that a PSE draft IEEE
802.3at (D3.0) compliant may apply more than two fingers,
but the final result will be the same as two fingers).
Table 4. Single and Dual Event Classification
The NCP1083 can handle all defined types of
In the IEEE 802.3af standard the classification is
For power injectors and midspans a pure physical
Since switches can establish a data link between PSE and
An IEEE 802.3af compliant PSE performs only One
A draft IEEE 802.3at (D3.0) compliant PSE using this
The PSE will generate the sequence described in Figure 8.
Standard
802.3af
802.3at
802.3at
Layer
1
1
2
Single event physical classification
Two event physical classification
Data-link (IP) communication classi-
fication
Handshake