ncp1083 ON Semiconductor, ncp1083 Datasheet - Page 13

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

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Power Mode
PSE and PD devices move into the operating mode.
Under Voltage Lock Out (UVLO)
(UVLO) circuit which monitors the input voltage and
determines when to apply power to the DC−DC controller.
UVLO must be connected to VPORTN
signature resistor has to be placed directly between
VPORTP and VPORTN
must be connected to the center of an external resistor
divider between VPORTP and VPORTN
Figure 12. The series resistance value of the external
resistors must add to 25.5 kW and replaces the internal
signature resistor.
When the classification hand−shake is completed, the
The NCP1083 incorporates an under voltage lock out
To use the default settings for UVLO (see Table 3), the pin
To define the UVLO threshold externally, the UVLO pin
The PSE performed a one event hardware classification
(it can be a IEEE 802.3af or a draft IEEE 802.3at
(D3.0) compliant PSE with Layer 2 engine).
The PSE performed a two event hardware classification
but it did not properly control the input voltage in the
mark voltage window, (for example it crossed the reset
range).
VPORT
Figure 11. Default UVLO Settings
Figure 13. Front and Rear Auxiliary Supply Input with Support for Very Low Input Voltages
VPORT
Rdet
1,2
POE(+)
for very low
VAUX(−)
VAUX only
POE(−)
Optional −
, as shown in Figure 11.
VAUX(+)
UVLO
VPORTN1,2
VPORTP
NCP1083
Raux1
Raux3
Or
Raux2
1,2
. In this case the
1,2
to VPORTN1,2 (Front AUX Configuration)
to RTN (Rear AUX Configuration)
as shown in
Rdet2
Rdet1
D1
D2
http://onsemi.com
13
VPORTN1,2
R2 can be calculated using the following equations:
an external reference voltage hysteresis of 15 percent typical.
Auxiliary Supply Support
networks and minimize the bill of materials, the NCP1083
supports drawing power from an external supply. The
NCP1083 supports the IEEE 802.3af/at standard when PoE
power sourcing is available and acts as a regular DC−DC
converter when there is no power source available on the
Ethernet cable as shown in Figure 13.
ways depending on where the auxiliary supply is injected.
The front, rear and direct auxiliary supply configurations are
explained in more detail in the application note
“NCP1083−3 PoE Auxiliary Supply Applications”.
UVLO
AUX
VPORTP
For a Vuvlo_on desired turn−on voltage threshold, R1 and
When using the external resistor divider, the NCP1083 has
To support applications connected to non−PoE enabled
Auxiliary supply support can be implemented in three
NCP1083
VPORT
Figure 12. External UVLO Configuration
Switch
Pass
RTN
R1
R2
R1 ) R2 + R
R2 +
DC−DC Stage
Cpd
V
ulvo_on
1.2
UVLO
VPORTN1,2
VPORTP
det
R
det
NCP1083