參數(shù)資料
型號(hào)： DC859A
廠商： Linear Technology
文件頁(yè)數(shù)： 2/32頁(yè)
文件大?。?/td> 0K
描述： EVAL BOARD FOR LTC4267
設(shè)計(jì)資源： DC859A Design File
DC859A Schematic
標(biāo)準(zhǔn)包裝： 1
主要目的： 電源管理，以太網(wǎng)供電（POE）
嵌入式： 否
已用 IC / 零件： LTC4267
已供物品： 板
LTC4267
10
4267fc
specied to avoid corrupting the 25kΩ signature resistor
while also saving board space and cost. In addition, the in-
rush current limit requirement of the IEEE 802.3af standard
can cause large transient power dissipation in the PD. The
LTC4267 is designed to allow multiple turn-on sequences
without overheating the miniature 16-lead package. In the
event of excessive power cycling, the LTC4267 provides
thermal overload protection to keep the onboard power
MOSFET within its safe operating area.
OPERATION
The LTC4267 PD interface has several modes of opera-
tion depending on the applied input voltage as shown in
Figure 1 and summarized in Table 1. These modes satisfy
the requirements dened in the IEEE 802.3af specication.
The input voltage is applied to the VPORTN pin and must
be negative relative to the VPORTP pin. Voltages in the data
sheet for the PD interface portion of the LTC4267 are with
respect to VPORTP while the voltages for the switching
regulator are referenced to PGND. It is assumed that PGND
is tied to POUT. Note the use of different ground symbols
throughout the data sheet.
Table 1. LTC4267 Operational Mode
as a Function of Input Voltage
INPUT VOLTAGE
(VPORTN with RESPECT to VPORTP) LTC4267 MODE OF OPERATION
0V to – 1.4V
Inactive
–1.5V to –9.5V**
25kΩ Signature Resistor Detection
–9.8V to –12.4V
Classication Load Current Ramps up
from 0% to 100%
–12.5V to UVLO*
Classication Load Current Active
UVLO* to –57V
Power Applied to Switching Regulator
*VPORTN UVLO includes hysteresis.
Rising input threshold – 36.0V
Falling input threshold –30.5V
**Measured at LTC4267 pin. The LTC4267 meets the IEEE 802.3af 10V
minimum when operating with the required diode bridges.
APPLICATIO S I FOR ATIO
WU
UU
Figure 1. Output Voltage, PWRGD and PD
Current as a Function of Input Voltage
DETECTION V1
CLASSIFICATION
UVLO
TURN-ON
UVLO
OFF
POWER
BAD
UVLO
OFF
UVLO
ON
UVLO
TURN-OFF
τ = RLOAD C1
PWRGD TRACKS
VPORTN
DETECTION V2
–10
TIME
–20
–30
V
PORTN
(V)
–40
–50
–10
TIME
–20
–30
P
OUT
(V)
–40
–50
–10
TIME
–20
–30
PWRGD
(V)
–40
–50
ICLASS
PD
CURRENT
ILIM_LO
dV
dt
ILIM_LO
C1
=
POWER
BAD
POWER
GOOD
DETECTION I1
CLASSIFICATION
ICLASS
DETECTION I2
LOAD, ILOAD (UP TO ILIM_HI)
CURRENT
LIMIT, ILIM_LO
4267 F01
ICLASS DEPENDENT ON RCLASS SELECTION
ILIM_LO = 140mA (NOMINAL), ILIM_HI = 375mA (NOMINAL)
I1 =
V1 – 2 DIODE DROPS
25k
ILOAD =
(UP TO ILIM_HI)
VOUT
RLOAD
I2 =
V2 – 2 DIODE DROPS
25k
VPORTP
PSE
IIN
LTC4267
R9
RCLASS
RLOAD
VOUT
C1
RCLASS
PWRGD
POUT
PGND
VPORTN
VIN
TIME
VOLTAGES WITH RESPECT TO VPORTP
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