Datasheet

VEE
+
-
to dc current limit
LM5072
6
7
DCCL
1.25V
R
DCCL
R
DCCL
(k:) =
x 127.5 k:
I
DC (mA)
100 mA
VEE
+
-
to inrush current limit
LM5072
5
7
50 PA
to FAUX
1.25V
ICL_FAUX
R
ICL
R
ICL
(k:) =
100 mA
I
INRUSH (mA)
x 127.5 k:
LM5072
www.ti.com SNVS437D –MARCH 2006–REVISED APRIL 2013
To adjust the capacitor charging time for a particular application requirement, the inrush limit can be programmed
to any value between 150 and 400 mA with an external resistor (R
ICL
) between the ICL_FAUX and VEE pins, as
shown in Figure 20. The relationship between the R
ICL
value and the desired inrush current limit I
INRUSH
satisfies
the following equation:
(1)
Figure 20. Input Inrush Limit Programming via R
ICL
The inrush current causes a voltage drop along the PoE Ethernet cable (20Ω maximum) that reduces the input
voltage sensed by the LM5072. To avoid erratic turn-on (hiccups), I
INRUSH
should be programmed such that the
input voltage drop due to cable resistance does not exceed the V
IN-UVLO
hysteresis (6V minimum).
DC Current Limit Programming
The LM5072 provides a default DC current limit of 440 mA nominal. This default limit can be selected by leaving
the DCCL pin open.
The LM5072 allows the DC current limit to be programmed within the range from 150 mA to 800 mA. Figure 21
shows the method to program the DC current limit with an external resistor, R
DCCL
. The relationship between the
R
DCCL
value and the desired DC current limit I
DC
satisfies the following equation:
(2)
Figure 21. Input DC Current Limit Programming via R
DCCL
Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LM5072