LT3837EFE-PBF LINER [Linear Technology], LT3837EFE-PBF Datasheet - Page 25

• Manufacturer Part Number: LT3837EFE-PBF
• Description: Isolated No-Opto Synchronous Flyback Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
PC Board Layout Considerations
In order to minimize switching noise and improve output
load regulation, connect the GND pin of the LT3837 directly
to the ground terminal of the V
the bottom terminal of the current sense resistor, the
ground terminal of the input capacitor, and the ground
plane (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 9 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.
CC
and GND pins on the IC package. This
LT3825
V
CC
C
VCC
GND
V
V
CC
LT3825
CC
SG
GND
CC
CC
capacitor immediately
decoupling capacitor,
V
CC
PG
TURN-OFF
TURN-ON
GATE
GATE
Figure 9. High Current Paths
•
T2
•
R
SENSE
MP
C
R
V
IN
Check that the maximum BV
are not exceeded due to inductive ringing. This is done by
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 fre-
quency 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
capacitor) and small-signal currents fl ow in the other
direction.
Keep the trace from the feedback divider tap to the FB
short to preclude inadvertent pickup.
For applications with multiple switching power converters
connected to the same input supply, make sure that the
input fi lter capacitor for the LTC3837 is not shared with
other converters. AC input current from another converter
could cause substantial input voltage ripple and this could
interfere with the LT3837 operation. A few inches of PC
trace or wire (L ≅ 100nH) between the C
and the actual source V
sharing problems.
C
VIN
Q4
Q3
TURN-OFF
•
•
TURN-ON
GATE
T1
GATE
•
MS
IN
is suffi cient to prevent current
DSS
3837 F09
C
OUT
OUT
ratings of the MOSFETs
IN
CC
of the LT3837
LT3837
decoupling
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