Datasheet
1
2
3
4
5
6
7
8
VSS
CLASS
N/C
DET
RTN
PG
VDD
ILIM
Detailed Pin Description
I
(LIM)
+
25000
R
(ILIM)
(1)
data sheet
TPS2375-1
TPS2377-1
SLVS570A – MARCH 2005 – REVISED APRIL 2008 .........................................................................................................................................................
www.ti.com
TPS2375-1/77-1
(TOP VIEW)
TERMINAL FUNCTIONS
PIN NAME PIN NUMBER I/O DESCRIPTION
Connect a resistor from ILIM to VSS to set the start-up inrush current limit. The
ILIM 1 O equation for calculating the resistor is shown in the detailed pin description section for
ILIM.
Connect a resistor from CLASS to VSS to set the classification of the powered device
CLASS 2 O (PD). The IEEE classification levels and corresponding resistor values are shown in
Table 1 .
DET 3 O Connect a 24.9-k Ω detection resistor from DET to VDD for a valid PD detection.
VSS 4 I Return line on the source side of the TPS2375-1 from the PSE.
Switched output side return line used as the low-side reference for the TPS2375-1
RTN 5 O
load.
PG 6 O Open-drain, power-good output; active high.
NC 7 No connection
VDD 8 I Positive line from the rectified PSE provided input.
The following descriptions refer to the schematic of Figure 1 and the functional block diagram.
ILIM: A resistor from this pin to VSS sets the inrush current limit per Equation 1 :
where ILIM is the desired inrush current value, in amperes, and R
(ILIM)
is the value of the programming resistor
from ILIM to VSS, in ohms. The practical limits on R
(ILIM)
are 62.5 k Ω to 500 k Ω . A value of 178 k Ω is
recommended for compatibility with legacy power sourcing equipment (PSE).
Inrush current limiting prevents current drawn by the bulk capacitor from causing the line voltage to sag below
the lower UVLO threshold. Adjustable inrush current limiting allows the use of arbitrarily large capacitors and also
accommodates legacy systems that require low inrush currents.
The ILIM pin must not be left open or shorted to VSS.
CLASS: Classification is implemented by means of an external resistor, R
(CLASS)
, connected between CLASS
and VSS. The controller draws current from the input line through R
(CLASS)
when the input voltage lies between
13 V and 21 V. The classification currents specified in the electrical characteristics table include the bias current
flowing into VDD and any RTN leakage current.
Table 1. CLASSIFICATION
CLASS PD POWER (W) R
(CLASS)
( Ω ) 802.3af LIMITS (mA) NOTE
0 0.44 – 12.95 4420 ± 1% 0 - 4 Default class
1 0.44 – 3.84 953 ± 1% 9 – 12
2 3.84 – 6.49 549 ± 1% 17 – 20
3 6.49 – 12.95 357 ± 1% 26 – 30
4 - 255 ± 1% 36 – 44 Reserved for future use
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