LM3248

PVIN_

BOOST

SW_BOOST

SW_

BUCK

FB_

BUCK

VCON

PGND SGND

ENABLE

MODE

VBATT

VOUT

ACB

BOOST GATE

VCC_PA_2G

BB or

RFIC

DAC

GPO2

GPO1

BGND

1.5 µH

10 µF

2.2 µF

PA

4.7 µF

PA(s)

VCC_PA_3G

1 nF

GPO3

1.0 µH

L1

10 µF

C2

C1

10 nF

C34

C27

1 µF

Lo ESL

C28

10 µF

L3

C7

3.3 nF

C8

C3

C20

C5

3.3 nF

C19

330 pF

VBATT_PA

VBATT_PA

U2

LM3248

www.ti.com

SNVSA01A – JULY 2013 – REVISED SEPTEMBER 2013

To help minimize noise coupled back into power supplies:

•

Use a star connection to route from the VBATT power source to the LM3248 PVIN_BOOST pins and to

the PA device VBATT pins.

•

Include sufficient decoupling capacitance, for both low and high frequency, at the PA VBATT connections.

•

Route traces for minimum inductance (short, wide connections) between supply pins and bypass capacitor(s).

•

Route traces to minimize inductance between bypass capacitors and the ground plane.

•

Utilize necessary power supply trace inductance(s) to reduce coupling between function blocks.

•

Inserting a ferrite bead in series with the VBATT power supply trace may offer a favorable tradeoff between

board area and additional shunt bypass capacitors, by attenuating noise that might otherwise propagate

through the supply connections.

4. LM3248 RF Evaluation Board

Figure 29. Simplified LM3248 RF Evaluation Board Schematic

LM3248 PCB Placement Considerations

1. Input Capacitor C2 should be placed closer to LM3248 than C1.

2. Optional to add a 1 nF (C34) capacitor on the input of LM3248 for high frequency filtering.

3. Bulk Output Capacitor C7 should be placed closer to LM3248 than C8.

4. Connect GND terminals of C7, C8 and C34 directly to System RF GND layer of phone board.

5. Connect GND terminals of boost output C27 and buck input C28 capacitors to copper PGND island on the

component side. This island is then tied to the system ground layer through several vias.

6. Connect bumps SGND_BOOST(B2), SGND_BUCK(C3), DGND(E3), and BGND (F3) directly to system

ground layer.

7. Small high-frequency filtering capacitors (e.g., C34) work better when they are connected to system ground

instead of the PGND island. These capacitors should be 0201 (0603 metric) or 01005 (0402 metric) case

size for minimum footprint and best high frequency characteristics.

Copyright © 2013, Texas Instruments Incorporated

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