CS3511

16

DS845PP2

5. POWER SUPPLY, GROUNDING, AND PCB LAYOUT

5.1

Power Supply and Grounding

The CS3511 requires careful attention to power supply and grounding arrangements if its potential perfor-

mance is to be realized.

Extensive use of power and ground planes, ground plane fill in unused areas and surface mount decoupling

capacitors are recommended. It is necessary to de-couple the power supply by placing capacitors directly

between the power and ground of the CS3511. Decoupling capacitors should be as close to the pins of the

CS3511 as possible. The lowest value ceramic capacitor should be closest to the pin and should be mount-

ed on the same side of the board as the CS3511 to minimize inductance effects. The CRD3511 reference

design demonstrates the optimum layout and power supply arrangements.

5.1.1

Maximum Supply Voltage

The absolute maximum allowable voltage on the VP supply pins (pins 10, 15 and 20) is shown in the Ab-

solute Maximum Ratings table. Device damage can occur above this voltage. Please note that the abso-

lute maximum voltage does not represent a valid operating condition. The maximum voltage on the VP

pins during operation is shown in the Recommended Operating Conditions table.

During normal operation, the output pins (pins 9, 12, 13, and 16) may experience overshoot voltages due

to inductive kickback. Care should be taken to properly de-couple the VP pins because overshoot on the

output pins can travel through the CS3511 output devices and appear on the VP pins. Without proper

power supply decoupling, this can cause ripple voltages on the VP pins that might exceed their absolute

maximum voltage shown in the Absolute Maximum Ratings table. However, this will only happen in ex-

treme cases and can be prevented by placing the high-frequency decoupling capacitors close to the VP

pins.

5.2

QFN Thermal Pad

The CS3511 is available in a compact QFN package. The underside of the QFN package reveals a large

metal pad that serves as a thermal relief to provide for maximum heat dissipation. This pad must mate with

an equally dimensioned copper pad on the PCB and must be electrically connected to PGND. A series of

thermal vias should be used to connect this copper pad to one or more larger ground planes on other PCB

layers; the copper in these ground planes will act as a heat sink for the CS3511. The CRD3511 reference

design demonstrates the optimum thermal pad and via configuration.

5.3

Layout Considerations

The CS3511 is a power (high current) amplifier that operates at relatively high switching frequencies. The

outputs of the amplifier switch between the supply voltage and ground, at high speeds, while driving high

currents. This high-frequency digital signal is passed through an LC low-pass filter to recover the amplified

audio signal. Since the amplifier must drive the inductive LC output filter and speaker loads, the amplifier

outputs can be pulled above the supply voltage and below ground by the energy in the output inductance.

Additionally, the CS3511’s junction temperature rises when supplying power to loads and relies on the PCB

for heat sinking.

To avoid subjecting the CS3511 to potentially damaging voltage stress and output-power-limiting elevated

junction temperatures, it is critical to have a good printed circuit board layout. It is strongly recommended

that the Cirrus CRD3511 layout be used for all applications and only be deviated from after careful analysis

of the effects of any changes. Please refer to Cirrus Logic application note AN315 for further information

regarding the layout of the CS3511.