LTC3852 datasheet(27/32 Pages) LINER

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LTC3852

3852f

LTC3852

CC1

CC2

CFF

CINTVCC

CFLY

RS1

CSS

CFLTR

RFREQ

RPGOOD

VPULL-UP

COUT1

CIN2

COUT2

RSENSE

–

VIN

–

VOUT

3852 F13

PGOOD

FREQ/PLLFLTR

MODE/PLLIN

RUN

SHDN

TRACK/SS

ITH

VFB

SENSE–

SENSE+

BOOST

VIN2

VIN1

INTVCC

VPUMP

GND1, 2

C–

C+

RS2

OFF

Figure 13. LTC3852 Switching Regulator Layout Diagram

APPLICATIONS INFORMATION

ground. The 47pF to 100pF capacitor should be as

close as possible to the LTC3852. Be careful locating

the feedback resistors too far away from the LTC3852.

The VFB line should not be routed close to any other

nodes with high slew rates.

3. Are the SENSE– and SENSE+ leads routed together

with minimum PC trace spacing? The ﬁlter capacitor

between SENSE+ and SENSE– should be as close as

possible to the LTC3852. Ensure accurate current

sensing with Kelvin connections as shown in Figure 14.

Series resistance can be added to the SENSE lines to

increase noise rejection and to compensate for the ESL

of RSENSE.

4. Does the (+) terminal of CIN connect to the drain of

the topside MOSFET(s) as closely as possible? This

capacitor provides the AC current to the MOSFET(s).

5. Is the INTVCC ceramic decoupling capacitor connected

closely between INTVCC and GND2? This capacitor

carries the MOSFET driver peak currents.

6. Keep the switching node (SW), top gate node (TG) and

boost node (BOOST) away from sensitive small-signal

SENSE+ SENSE–

HIGH CURRENT PATH

3852 F14

CURRENT SENSE

RESISTOR

(RSENSE)

nodes, especially from the voltage and current sensing

feedback pins. All of these nodes have very large and

fast moving signals and therefore should be kept on

the “output side” of the LTC3852 and occupy minimum

PC trace area.

Figure 14. Kelvin Sensing RSENSE

Layout Considerations (Charge Pump)

Due to the high switching frequency and high transient

currents produced by the charge pump, careful board layout

is necessary for optimum performance. A true ground

plane and short connections to all the external capacitors

LTC3852 Datasheet(PDF) 27 Page - Linear Technology

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