______________________________________________________________________________________ 43
MAX5971B
Single-Port, 40W, IEEE 802.3af/at,
PSE Controller with I
2
C
Applications Information
Layout Procedure
Careful PCB layout is critical to achieve high efficiency
and low EMI. Follow these layout guidelines for optimal
performance.
1) Place the high-frequency input bypass capacitor (0.1FF
ceramic capacitor from AGND to V
EE
) and the output
bypass capacitor (0.1FF ceramic capacitor from AGND
to OUTP) as close as possible to the MAX5971B.
2) Use large SMT component pads for power dissipat-
ing devices, such as the MAX5971B and the external
diodes in the high-power path.
3) Use short, wide traces whenever possible for high-
power paths.
4) Use the MAX5971B Evaluation Kit as a design and
layout reference.
5) The EP must be soldered evenly to the PCB ground
plane (V
EE
) for proper operation and power dissipa-
tion. Use multiple vias beneath the EP for maximum
heat dissipation. A 1.0mm to 1.2mm pitch is the
recommended spacing for these vias and should
be plated (1oz copper) with a small barrel diameter
(0.30mm to 0.33mm).
Figure 15. Typical Operating Circuit 1 (DC Load Removal Detection, Internal PWM Enabled for LED Indication, and Class 5
Detection Enabled)
Table 40. Register Summary (continued)
5.1kI
1kI
1kI
2.2MI
0.1µF
100V
SMJ58A
-54V
-54V
47µF
100V
0.1µF
100V
1N4448
1N4448
10mH
1nF
AGND
SERIAL INTERFACE
SDA SCL AD0 INT
V
EE
V
EE_DIG
EN
LED
LED
LEGACY
MIDSPAN
OSC
OUT
OUTP
PWMEN
DET
ILIM1
ILIM2
MAX5971B
PSE OUTPUT
ADDR REGISTER NAME R/W BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
RESET
STATE
CURRENT READOUT
30H Port Current (MSB) R IPD[8] IPD[7] IPD[6] IPD[5] IPD[4] IPD[3] IPD[2] IPD[1]
0000 to
0000
31H Port Current (LSB) R Reserved Reserved Reserved Reserved Reserved Reserved Reserved IPD[0]
0000 to
0000
32H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
33H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
34H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
35H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
36H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
37H Reserved — Reserved Reserved Reserved Reserved Reserved Reserved Reserved Reserved —
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