LTC3704 LINER [Linear Technology], LTC3704 Datasheet - Page 24

• Manufacturer Part Number: LTC3704
• Description: Wide Input Range, No RSENSE Positive-to-Negative DC/DC Controller
• Manufacturer: LINER [Linear Technology]

LTC3704
APPLICATIO S I FOR ATIO
2. Beware of ground loops in multiple layer PC boards. Try
3. Place the C
4. The high di/dt loop from the drain of the power MOSFET,
5. Check the stress on the power MOSFET by measuring
24
to maintain one central ground node on the board and
use the input capacitor to avoid excess input ripple for
high output current power supplies. If the ground plane
is to be used for high DC currents, choose a path away
from the small-signal components.
INTV
carries high di/dt MOSFET gate drive currents. A low
ESR X5R-dielectric 4.7 F ceramic capacitor works well
here.
through the coupling capacitor and back through the
diode to ground should be kept as tight as possible to
reduce inductive ringing. Excess inductance can cause
increased stress on the power MOSFET and increase HF
noise on the drain node. It is also important to keep the
cathode of the diode as close as possible to the MOSFET
source or the bottom of the sense resistor.
its drain-to-source voltage directly across the device
terminals (reference the ground of a single scope probe
directly to the source pad on the PC board). Beware of
inductive ringing which can exceed the maximum speci-
fied voltage rating of the MOSFET. If this ringing cannot
be avoided and exceeds the maximum rating of the
device, either choose a higher voltage device or specify
an avalanche-rated power MOSFET. Not all MOSFETs
are created equal (some are more equal than others).
CC
and GND pins on the IC package. This capacitor
VCC
capacitor immediately adjacent to the
U
U
W
U
6. Place the small-signal components away from high
7. If a sense resistor is used in the source of the power
8. For optimum load regulation and true remote sensing,
9. For applications with multiple switching power con-
frequency switching nodes. In the layout shown in
Figure 22, all of the small-signal components have been
placed on one side of the IC and all of the power
components have been placed on the other. This also
allows the use of a pseudo-Kelvin connection for the
signal ground, where high di/dt gate driver currents
flow out of the IC ground pin in one direction (to the
bottom plate of the INTV
small-signal currents flow in the other direction.
MOSFET, minimize the capacitance between the SENSE
pin trace and any high frequency switching nodes. The
LTC3704 contains an internal leading edge blanking
time of approximately 180ns, which should be ad-
equate for most applications.
the top of the output resistor divider should connect
independently to the top of the output capacitor (Kelvin
connection), staying away from any high dV/dt traces.
Place the divider resistors near the LTC3704 in order to
keep the high impedance FB node short.
verters connected to the same input supply, make sure
that the input filter capacitor for the LTC3704 is not
shared with other converters. AC input current from
another converter could cause substantial input voltage
ripple, and this could interfere with the operation of the
LTC3704. A few inches of PC trace or wire (L 100nH)
between the C
V
problems.
IN
should be sufficient to prevent current sharing
IN
of the LTC3704 and the actual source
CC
decoupling capacitor) and
sn3704 3704fs