PTB48540AAH_14 Datasheet, PDF (8/13 Pages) Texas Instruments – 10-W Power-Over-Ethernet Isolated Power Module Assembly

Application Notes
PTB48540 Series
Not Recommended for New Designs
Using the Output Inhibit Control with the
PTB48540 Power-over-Ethernet Modules
The PTB48540 Power-over-Ethernet (PoE) modules
incorporate all the necessary interface requirements to
provide 10 W of regulated DC voltage from a recognized
Power-over-Ethernet source.
One of the operating features of these modules allows
the output voltage to be turned off, thereby placing the
module in an idle state. This may be useful for applica-
tions that have an alternative voltage source available,
such as a wall adapter.
The “Output Inihibit” control is provided by pin 13. The
module functions normally with this pin open-circuit,
providing a regulated output voltage whenever a valid
source voltage is supplied from the Ethernet connection.
When a low voltage is applied to pin 13, with respect to
the “Input Ref” terminal (pin 4), the output is turned off.
Even though the Ethernet source is still present.
Figure 3-1 is an application schematic, which shows how
the “Output Inhibit” control may be used. Either a discrete
transistor (Q₁), or a contact switch may be used. The
“Output Inhibit” control pin has its own internal pull-up
(See notes 2 & 3). Table 3-1 gives the threshold require-
ments.
When placed in the “Off” state, the standby current
drawn from the input source is typically reduced to 1 mA ³.
Table 3-1; Pin 13 Output Inhibit Control Parameters ¹
Parameter
Min
Typ
Max
Enable (VIH)
4.5 V
Disable (VIL)
—
Vo/c [Open-Circuit]
Iin [pins 13 & 4 connnected] —
—
—
5V
–1 mA
—
0.8 V
—
Figure 3-1
+48 V
0V
1 =Output Off
5
6
12
11
A- Detect -B
A- Class -B
10 _{Data Line A}
9 _{Data Line B}
3
+V_OUT
4
Input Ref
PTB48540A
8
Spare Line A
2
Adjust
7
Spare Line B
1
–V_OUT
Output Inhibit
13
Q₁
BSS138
Alternate
On/Off
Contact/Switch
+5 V
0V
Turn-On Time: In the circuit of Figure 3-1, turning Q₁ on
applies a low-voltage to pin 13 and disables the module
output. Correspondingly, turning Q₁ off allows pin 13 to
be pulled high by an internal pull-up resistor. The module
produces a regulated output voltage within 60 ms. Figure
3-2 shows shows the output response of a PTB48540A
(5 V) following the turn-off of Q₁. The turn off of Q₁
corresponds to the drop in Q₁ Vgs. Although the rise-time
of the output voltage is short (<5 ms), the indicated delay
time will vary depending upon the input voltage and the
module’s internal timing. The waveform was measured
with a 48 Vdc input voltage, and a 1.4 A resistive load.
Figure 3-2
Notes:
1. The Output Inhibit control uses Input Ref (pin 4) as its
0-V reference. All voltages specified are with respect to
the Input Ref pin.
2. Use an open-collector device (preferably a discrete
transistor or switch) for the Output Inhibit input. A
pull-up resistor is not necessary. To turn the output
off, the control pin should be pulled low to less than
0.8 VDC.
3. The module’s idle current is typically less than 1 mA.
This is below the minimum power signature (MPS)
current, required for the PoE source to continue providing
the PD with a source voltage. This will inevitably result
in the removal of the module’s input source. However,
the PSE will endevour to periodically re-apply input
power after detecting that the PD is still a valid device.
This cycle may be prevented by also modifying the
module’s ‘Detect’ signature resistance so that it reflects
an invalid device to the PSE.
Delay Time
HORIZ SCALE: 10ms/Div
Vo (2V/Div)
Iin (0.2A/Div)
Q1Vgs (10V/Div)
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