LTC4278CDKD#PBF Linear Technology, LTC4278CDKD#PBF Datasheet - Page 38

• Manufacturer Part Number: LTC4278CDKD#PBF
• Description: IC PD IEEE 802.3AT 25.5W 32-DFN
• Manufacturer: Linear Technology

Specifications of LTC4278CDKD#PBF

• Controller Type: Powered Device Interface Controller (PD)
• Interface: IEEE 802.3af
• Voltage - Supply: 4.5 V ~ 20 V
• Current - Supply: 6.4mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 32-DFN
• Input Voltage: 60V
• Supply Current: 1.35mA
• Digital Ic Case Style: DFN
• No. Of Pins: 32
• Duty Cycle (%): 88%
• Frequency: 100kHz
• Operating Temperature Range: °C To +70°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC4278
to the ground terminal of the V
the bottom terminal of the current sense resistor and the
ground terminal of the input capacitor, using a ground plane
with multiple vias. Place the V
adjacent to the V
capacitor carries high di/dt MOSFET gate drive currents.
Use a low ESR ceramic capacitor.
Take care in PCB layout to keep the traces that conduct high
switching currents short, wide and with minimal overall
loop area. These are typically the traces associated with
the switches. This reduces the parasitic inductance and
also minimizes magnetic fi eld radiation. Figure 19 outlines
the critical paths.
Keep electric fi eld radiation low by minimizing the length
and area of traces (keep stray capacitances low). The drain
of the primary-side MOSFET is the worst offender in this
category. Always use a ground plane under the switcher
circuitry to prevent coupling between PCB planes.
Check that the maximum BV
are not exceeded due to inductive ringing. This is done by
APPLICATIONS INFORMATION
38
CC
V
CC
and GND pins on the IC package. This
V
C
CC
VCC
SG
V
CC
DSS
V
CC
CC
CC
PG
ratings of the MOSFETs
capacitor immediately
decoupling capacitor,
TURN-OFF
TURN-ON
GATE
Figure 19. Layout Critical High Current Paths
GATE
•
T2
•
R
SENSE
MP
+
V
IN
C
viewing the MOSFET node voltages with an oscilloscope. If
it is breaking down, either choose a higher voltage device,
add a snubber or specify an avalanche-rated MOSFET.
Place the small-signal components away from high frequen-
cy switching nodes. This allows the use of a pseudo-Kelvin
connection for the signal ground, where high di/dt gate
driver currents fl ow out of the IC ground pin in one direction
(to the bottom plate of the V
small-signal currents fl ow in the other direction.
Keep the trace from the feedback divider tap to the FB pin
short to preclude inadvertent pick-up.
For applications with multiple switching power converters
connected to the same input supply, make sure that the
input fi lter capacitor for the LTC4278 is not shared with
other converters. AC input current from another converter
could cause substantial input voltage ripple which could
interfere with the LTC4278 operation. A few inches of PC
trace or wire (L ≅ 100nH) between the C
and the actual source V
sharing problems.
VIN
+
•
•
C
T1
R
•
Q4
Q3
TURN-OFF
TURN-ON
GATE
GATE
IN
, is suffi cient to prevent current
CC
decoupling capacitor) and
MS
+
IN
4278 F19
of the LTC4278
C
OUT
OUT
4278fa