LTM8031MPV#PBF datasheet(13/22 Pages) LINER

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LTM8031

8031fb

applicaTions inForMaTion

4. Place the CIN and COUT capacitors such that their

ground currents flow directly adjacent or underneath

the LTM8031.

5. Connect all of the GND connections to as large a copper

pour or plane area as possible on the top layer. Avoid

breaking the ground connection between the external

components and the LTM8031.

6. Use vias to connect the GND copper area to the board’s

internalgroundplane.LiberallydistributetheseGNDvias

to provide both a good ground connection and thermal

path to the internal planes of the printed circuit board.

Hot-Plugging Safely

The small size, robustness and low impedance of ceramic

capacitors make them an attractive option for the input

bypass capacitor of LTM8031. However, these capacitors

can cause problems if the LTM8031 is plugged into a live

or fast rising or falling supply (see Linear Technology

Application Note 88 for a complete discussion). The low

loss ceramic capacitor combined with stray inductance in

series with the power source forms an under-damped tank

circuit, and the voltage at the VIN pin of the LTM8031 can

ring to twice the nominal input voltage, possibly exceed-

ing the LTM8031’s rating and damaging the part. A similar

phenomenoncanoccurinsidetheLTM8031module,atthe

output of the integrated EMI filter, with the same potential

of damaging the part.

If the input supply is poorly controlled or the user will be

plugging the LTM8031 into an energized supply, the input

networkshouldbedesignedtopreventthisovershoot.Fig-

ure 4 shows the waveforms that result when an LTM8031

circuit is connected to a 24V supply through six feet of 24-

gauge twisted pair. The first plot (4a) is the response with

a 2.2µF ceramic capacitor at the input. The input voltage

Figure 3. Layout Showing Suggested External Components,

GND Plane and Thermal Vias

GND

COUT

CIN

8031 F03

VIN

FIN

RUN/SS

SYNC

AUX

BIAS

VOUT

GND

OPTIONAL

FIN

CAPACITOR

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