TPS23753A
SLVS933B –JULY 2009–REVISED JANUARY 2010
www.ti.com
V
V
C
DD1
Oscillator
FRS
CTL
enb
CONV.
OFF
Control
800ms
Soft Start
50kW
50kW
enb
-
-
+
GATE
1
D
CK
Q
+
0.75V enb
CLRB
40mA
(pk)
RTN
Blank
Switch
Matrix
Converter
Thermal
Monitor
2.875kW
V
B
Regulator
Reference
CS
+
0.55V
-
RTN
1.5V
&1.2V
BLNK
APDb
2.53V
APD
CLS
V
DD
11.5V &
9.5V
Class
Regulator
AUXb
22V &
21.25V
VSS
DEN
12.5V
& 1V
400ms
Common
Circuits and
PoE Thermal
Monitor
S
R
Q
CONV.
OFF
1
0
ILIMb
H
L
+
-
35V &
30.5V
EN
V
RTN
SS
80mW
4.5V
AUXb
APDb
Figure 2. TPS23753A Functional Block Diagram
Pin Description
See Figure 1 for component reference designators (RCS for example ), and the Electrical Characteristics table for
values denoted by reference (VCSMAX for example). Electrical Characteristic values take precedence over any
numerical values used in the following sections.
APD
APD forces power to come from an external adapter connected from VDD1 to RTN by opening the hotswap
switch. A resistor divider is recommended on APD when it is connected to an external adapter. The divider
provides ESD protection, leakage discharge for the adapter ORing diode, and input voltage qualification. Voltage
qualification assures the adapter can support the PD before the PoE current is cut off.
Select the APD divider resistors per the following equations where VADPTR-ON is the desired adapter voltage that
enables the APD function as adapter voltage rises.
R
= R
x V
(
-V
V
APDEN
)
APD1
APD2
ADPTR _ ON
APDEN
(1)
6
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