LTC3785 LINER [Linear Technology], LTC3785 Datasheet - Page 24

• Manufacturer Part Number: LTC3785
• Description: High Efficiency, Synchronous, 4-Switch Buck-Boost Controller
• Manufacturer: LINER [Linear Technology]

LTC3789
applicaTions inForMaTion
• Use planes for V
• Flood all unused areas on all layers with copper. Flooding
• Segregate the signal and power grounds. All small-
• Place switch B and switch C as close to the controller
• Keep the high dV/dT SW1, SW2, BOOST1, BOOST2,
• The path formed by switch A, switch B, D1 and the C
24
filtering and to keep power losses low.
with copper will reduce the temperature rise of power
components. Connect the copper areas to any DC
net (V
board, the following checklist should be used to ensure
proper operation of the LTC3789. These items are also
illustrated in Figure 13.
signal components should return to the SGND pin at
one point, which is then tied to the PGND pin close to
the inductor current sense resistor R
as possible, keeping the PGND, BG and SW traces
short.
TG1 and TG2 nodes away from sensitive small-signal
nodes.
capacitor should have short leads and PC trace lengths.
The path formed by switch C, switch D, D2 and the
C
trace lengths.
OUT
V
IN
C
IN
capacitor also should have short leads and PC
IN
or GND). When laying out the printed circuit
QA
Figure 12. Switches Layout
D1
IN
and V
SW2
QB
LTC3789
R
SENSE
CKT
OUT
L
SW1
QC
to maintain good voltage
SENSE
D2
QD
.
V
C
GND
OUT
OUT
3789 F12
IN
• The output capacitor (–) terminals should be connected
• Connect the top driver boost capacitor C
• Connect the input capacitors C
• Connect V
• Route SENSE
• Connect the I
• Connect the INTV
as closely as possible to the (–) terminals of the input
capacitor.
BOOST1 and SW1 pins. Connect the top driver boost
capacitor C
C
carry the MOSFET AC current in the boost and buck
region.
C
may be connected closely to the LTC3789 SGND pin.
The R2 connection should not be along the high current
or noise paths, such as the input capacitors.
mum PC trace spacing. Avoid having sense lines pass
through noisy areas, such as switch nodes. The filter
capacitor between SENSE
close as possible to the IC. Ensure accurate current
sensing with Kelvin connections at the SENSE resistor.
One layout example is shown in Figure 14.
the IC, between I
capacitor helps to filter the effects of PCB noise and
output voltage ripple voltage from the compensa-
tion loop.
to the IC, between the INTV
pins. This capacitor carries the MOSFET drivers’ current
peaks. An additional 1µF ceramic capacitor placed im-
mediately next to the INTV
improve noise performance substantially.
OUT
OUT
closely to the power MOSFETs. These capacitors
and signal ground. A small V
FB
B
pin resistive dividers to the (+) terminals of
closely to the BOOST2 and SW2 pins.
TH
–
and SENSE
pin compensation network closely to
TH
CC
and the signal ground pins. The
bypass capacitor, C
+
CC
+
and SENSE
CC
leads together with mini-
and PGND pins can help
IN
and the power ground
and output capacitors
FB
bypass capacitor
–
A
closely to the
should be as
VCC
, closely
3789f