Datasheet > DI-102

DI-102

更新时间： 2022-04-23 23:00:11

品牌	Logo	应用领域
帕沃英蒂格盛 - POWERINT		以太网
页数	文件大小	规格书
2页	243K
描述
Lowered Overvoltage for Power over Ethernet (PoE)

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DI-102 数据手册

Design Idea DI-102

DPA-Switch^®Lowered Overvoltage

for Power over Ethernet (PoE)

Application

Device

Power Output

Input Voltage

Output Voltage

Topology

PoE/VoIP

DPA423G

36-57 VDC

Design Highlights

Operation

• Optimized overvoltage for PoE Powered Devices (PDʼs)

• Turn-off threshold 65 VDC and turn-on threshold

63 VDC

• Compliance to IEEE 802.3af standards over complete

voltage window ensures compatibility with power

sending equipment

This circuit allows the overvoltage shutdown threshold to be set

to approximately 63 VDC. The DPA-Switch detects the input

voltage via the current in L-pin resistor R_LS. Above the OV-off

threshold (135 µA), the DPA-Switch is disabled and below the

OV-onthreshold(131µA),theDPA-Switchbecomesoperational

again.Atstart-up,transistorQ2ispulledlow(off)viaresistorR5,

so as not to interfere with the under-voltage detection threshold.

Transistor Q2 is pulled high (on) via resistor R4 and will turn

on once the input voltage comfortably exceeds the under-

Wide Hysteresis Overvoltage

The default under-voltage and overvoltage shutdown

thresholds of the DPA-Switch are programmed with a single

resistor (R_LS) connected from the positive input voltage to the

L-pin. The default overvoltage and under-voltage thresholds

have a ﬁxed ratio (approximately 2.7:1).

voltage turn-on level, at the deﬁned threshold voltage (V_IN(th)

60 VDC). When turned-on, transistor Q2 connects the Control

pin (C) voltage (V_C) to the L-pin via R6, thus adding a ﬁxed

current (approximately 37 µA) to the L-pin. This additional

current lowers the OV on and off voltage thresholds.

The operating voltage range for PoE systems is 36 VDC to

57 VDC,amuchsmallerratio.OvervoltageShutdown(OVSD)

on the PD allows protection against possible system faults,

giving the design an increased level of robustness. This can

be achieved by adding a simple discrete circuit.

I_UV(ON)

I_OV(OFF)

R_LSOnly

OFF

100

131 µA

125

150

135 µA

I_L

47 µA

619 kΩ

R_LS

DC Input

Voltage

R_LSwith

Q2 Circuit

CONTROL

37 µA

OFF

DPA-Switch

100

125

150

I_L

PI-4065-083105

PI-4067-090105

L Pin Current (µA)

Figure 1. DPA-Switch with Lower OVSD (R₁= 10 MΩ,

R₂= 560 kΩ, R₃= 82 kΩ).

Figure 2. L-Pin Current without/with Wide OVSD Circuit.

DI-102

August 2005

www.powerint.com

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