LM2852 datasheet(11/13 Pages) NSC

11 / 13 page

Applications Information (Continued)

SPLIT-RAIL OPERATION

The LM2852 can be powered using two separate voltages

for AVIN and PVIN. AVIN is the supply for the control logic;

PVIN is the supply for the power FETs. The output filter

components need to be chosen based on the value of PVIN.

For PVIN levels lower than 3.3V, use output filter component

values recommended for 3.3V. PVIN must always be equal

to or less than AVIN.

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Layout Hints

These are several guidelines to follow while designing the

PCB layout for an LM2852 application.

The input bulk capacitor, C

IN, should be placed very

close to the PVIN pin to keep the resistance as low as

possible between the capacitor and the pin. High current

levels will be present in this connection.

All ground connections must be tied together. Use a

broad ground plane, for example a completely filled back

plane, to establish the lowest resistance possible be-

tween all ground connections.

The sense pin connection should be made as close to

the load as possible so that the voltage at the load is the

expected regulated value. The sense line should not run

too close to nodes with high EMI (such as the switch

node) to minimize interference.

The switch node connections should be low resistance

to reduce power losses. Low resistance means the trace

between the switch pin and the inductor should be wide.

However, the area of the switch node should not be too

large since EMI increases with greater area. So connect

the inductor to the switch pin with a short, but wide trace.

Other high current connections in the application such

as PVIN and V

OUT assume the same trade off between

low resistance and EMI.

Allow area under the chip to solder the entire exposed

die attach pad to ground. Lab measurements show im-

proved regulation performance when the exposed pad is

well grounded.

LM2852Y Example Circuit Schematic (500kHz)

Bill of Materials for 3.3V

IN to 1.8 VOUT Conversion

Part Number

Type

Size

Parameters

Qty

Vendor

LM2852YMXA-1.8

2A Buck

ETSSOP-14

NSC

DO3316P-153

Inductor

15 µH

Coilcraft

595D107X_6R3C2T

Capacitor

Case Code “C”

100 µF ±20%

Vishay-Sprague

GRM32ER60J476ME20B

Capacitor

1210

47µF/X5R/6.3V

Murata

INX

GRM21BR71C105KA01B

Capacitor

0805

1µF/X7R/16V

Murata

VJ0805Y272KXXA

Capacitor

0805

2.7nF ±10%

Vishay-Vitramon

CRCW060310R0F

Resistor

0603

Ω ±10%

Vishay-Dale

GRM21BR71C105KA01B

Capacitor

0805

1µF/X7R/16V

Murata

* If a “non-tantalum” solution is desired use an NOSC107M004R0150, 100 µF capacitor from AVX for CO.

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FIGURE 1.

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