LTC7802EUFDM datasheet(28/34 Pages) AD

28 / 34 page

LTC7802

Rev. 0

For more information www.analog.com

2. Are the signal and power grounds kept separate?

The combined IC ground pin and the ground return

of CINTVCC must return to the combined COUT (–) ter-

minals. The area of the “hot loop” formed by the top

N-channel MOSFET, bottom N-channel MOSFET and the

high frequency (ceramic) input capacitors, as shown

in Figure 8, should be minimized with short leads, pla-

nar connections, and multiple paralleled vias where

needed. The output capacitor (–) terminals should be

connected as close as possible to the (–) terminals of

the input capacitor.

3. Do the LTC7802 VFB pins’ resistive dividers connect to

the (+) terminals of COUT? The resistive divider must

be connected between the (+) terminal of COUT and

signal ground. Place the divider close to the VFB pin to

minimize noise coupling into the sensitive VFB node.

The feedback resistor connections should not be along

the high current input feeds from the input capacitor(s).

4. Are the SENSE– and SENSE+ leads routed together with

minimum PC trace spacing? Route these traces away

from the high frequency switching nodes, on an inner

layer if possible. The filter capacitor between SENSE+

and SENSE– should be as close as possible to the IC.

Ensure accurate current sensing with Kelvin connec-

tions at the sense resistor.

5. Is the INTVCC decoupling capacitor connected close

to the IC, between the INTVCC and the power ground

pin? This capacitor carries the MOSFET drivers’ cur-

rent peaks. An additional 1μF ceramic capacitor placed

immediately next to the INTVCC and GND pins can help

improve noise performance substantially. The boost

diodes should have separate routes directly to the

INTVCC capacitor near the IC, not shared with any sig-

nal connections to INTVCC.

APPLICATIONS INFORMATION

RL1

SW1

RSENSE1

VOUT1

COUT1

VIN

CIN

RIN

RL2

BOLD LINES INDICATE

HIGH SWITCHING

CURRENT. KEEP LINES

TO A MINIMUM LENGTH.

SW2

7802 F09

RSENSE2

VOUT2

COUT2

HOT

LOOP

HOT

LOOP

Figure 8. Branch Current Waveforms for Bucks

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