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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1351A
nal MOSFET which lies between the V
pins. This voltage charges C11 through a trickle
charge resistor, R3 to power the bias pin, Vin, of the
power supply controller. Once the bias power gets to
its V
threshold, the IC begins a controlled soft-
IN(ON)
start of the output. As this voltage rises, bias power
is taken over by T2, D1/2, and L1.
When the soft-start period is over, the output voltage
is regulated by the combination of the optoisolator
(U2) and the reference/error amplifier (D21) pulling
QUICK START PROCEDURE
Demonstration circuit 1351A is easy to set up to
evaluate the performance of the LTC4269IDKD-2 in a
PoE+ PD application. Refer to Figure 1 for proper
equipment setup and follow the procedure below:
When measuring the input or output voltage
NOTE:
ripple, care must be taken to avoid a long ground lead
on the oscilloscope probe. Measure the output (or
input) voltage ripple by touching the probe tip and
probe ground directly across the +VOUT and –VOUT
(or VPORT_P and VPORT_N) terminals. See Figure 2
for proper scope probe technique.
Place test equipment (voltmeter, ammeter, and
1.
electronic load) across output.
Input supplies:
2.
SINGLE OUTPUT, HIGH POWER, HIGH EFFICIENCY POE
and V
down on the COMP pin. The OUT and SOUT pins
PORTN
NEG
which drive Q3 and Q2, respectively, are Pulse Width
Modulated (PWM) in order to keep the output voltage
constant. The synchronous rectifiers (Q4 and Q5) on
the secondary side are self-driven by T2. This re-
duces the gate drive part's count and complexity
since no external driver ICs or delay circuits are
needed to achieve synchronous rectification. The high
efficiency that is expected with synchronous rectifica-
tion is maintained.
a.
to the RJ45 connector, J2. See Figure 1.
b.
(''Power Supply'' in Figure 1) across VPORT_P and
VPORT_N.
c.
iary Supply'' in Figure 1) capability, connect a 44V
to 57V capable power supply across AUX+ to AUX-.
Check for the proper output voltage of 5V.
3.
Once the proper output voltage is confirmed, adjust
4.
the load within the operating range and observe the
output voltage regulation, ripple voltage, efficiency
and other parameters.
Connect a PoE+ capable PSE with a CAT-5 cable
Or, connect a 37V to 57V capable power supply
If evaluating the auxiliary power supply (''Auxil-
2
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