器件名称: DI-102
功能描述: Lowered Overvoltage for Power over Ethernet (PoE)
文件大小: 242.72KB 共2页
简 介:Design Idea DI-102 DPA-Switch Lowered Overvoltage
for Power over Ethernet (PoE)
Application PoE/VoIP Device DPA423G Power Output Input Voltage 36-57 VDC Output Voltage Topology -
Design Highlights
Optimized overvoltage for PoE Powered Devices (PDs) 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
Operation
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 RLS. Above the OV-off threshold (135 A), the DPA-Switch is disabled and below the OV-on threshold (131 A), the DPA-Switch becomes operational again. At start-up, transistor Q2 is pulled low (off) via resistor R5, 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 undervoltage turn-on level, at the dened threshold voltage (VIN(th) = 60 VDC). When turned-on, transistor Q2 connects the Control pin (C) voltage (VC) to the L-pin via R6, thus adding a xed current (approximately 37 A) to the L-pin. This additional current lowers the OV on and off voltage thresholds.
Wide Hysteresis Overvoltage
The default under-voltage and overvoltage shutdown thresholds of the DPA-Switch are programmed with a single resistor (RLS) connected from the positive input voltage to the ……
