Description
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Description
TPS2378EVM-105 enables full evaluation of the TPS2378 device. Refer to the schematic shown in
. Ethernet power is applied from J1 to T1 and is dropped to the diode bridges (D4/D5/D10/D11 or
D6/D7/D12/D13) from the T1 center taps. The series R-C circuit from each center tap help balance the
Ethernet cable impedance and are critical for ESD and EMI/EMC performance. These circuits are
terminated at TP11 (EGND) through the high voltage capacitor, C11. At the output of the diode bridges is
the EMI/EMC filter and transient protection for the TPS2378. R9 provides the detection signature and R15
provides the class 4 signature resistance to the PSE.
To the right of the TPS2378 (U1) is the switched side of the PD controller. The TPS2378 RTN pin
provides inrush limited turn on and charge of the bulk capacitor, C4. During inrush, the TPS2378 CDB pin
is pulled low (with respect to the RTN pin). Since the CDB pin is connected to the GATE of Q1, Q1 is off
during inrush and J6 pin 1 is not connected to the RTN pin. This allows the output load to remain
connected during EVM testing.
Input power can also be applied at J3 from a dc source. EMI/EMC filtering is provided at this connector as
well and diode D1 ensures reverse voltage protection. R4 and R7 provide a threshold for the TPS2378
APD pin so that the TPS2378 internal MOSFET is disabled when the voltage at J3 is above approximately
38V. This ensures that the adapter has priority over the PSE source. LED’s D2 and D3 provide operational
visual indications of T2P and ON respectively.
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SLVU682 – March 2012
TPS2378 EVM User’s Guide
Copyright © 2012, Texas Instruments Incorporated
