SSM2317-MINI-EVALZ - Analog Devices Inc.

Evaluation Board for

Filterless Class-D Audio Amplifier

EVAL-SSM2317-MINI

Rev. 0

Evaluation boards are only intended for device evaluation and not for production purposes.

Evaluation boards are supplied “as is” and without warranties of any kind, express, implied, or

statutory including, but not limited to, any implied warranty of merchantability or fitness for a

particular purpose. No license is granted by implication or otherwise under any patents or other

intellectual property by application or use of evaluation boards. Information furnished by Analog

Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog

Devices for its use, nor for any infringements of patents or other rights of third parties that may

result from its use. Analog Devices reserves the right to change devices or specifications at any

time without notice. Trademarks and registered trademarks are the property of their respective

owners. Evaluation boards are not authorized to be used in life support devices or systems.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 www.analog.com

FEATURES

Single-ended and differential input capability

Small size board allows easy integration into custom

space-constrained applications (6.6 mm × 6.6 mm)

GENERAL DESCRIPTION

The SSM2317 is a fully integrated, single-chip, mono Class-D

audio amplifier. It is designed to maximize performance for

mobile phone applications. The application circuit requires a

minimum of external components and operates from a single

2.5 V to 5.5 V supply. It is capable of delivering 1.4 W of con-

tinuous output power with less than 1% THD + N, driving an

8 Ω load from a single 5.0 V supply.

The SSM2317 is equipped with a differential mode input port

and a high efficiency, full H-bridge at the output that enables

direct coupling of the audio power signal to the loudspeaker.

The differential mode input stage allows for cancelling of

common-mode noise.

The part also features a high efficiency, low noise output

modulation scheme that does not require external LC output

filters when attached to an inductive load. It operates with

85% efficiency at 1.4 W into 8 Ω from a 5.0 V supply and has

a signal-to-noise ratio (SNR) that is better than 93 dB.

Spread-spectrum modulation is used to provide lower EMI-

radiated emissions. The modulation provides high efficiency

even at low output power. Filterless operation also helps to

decrease distortion due to the nonlinearities of output LC filters.

This data sheet describes how to configure and use the SSM2317

mini evaluation board to test the SSM2317. It is recommended

that this data sheet be read in conjunction with the SSM2317

data sheet, which provides more detailed information about

the specifications, internal block diagrams, and application

guidance for the amplifier IC.

EVALUATION BOARD DESCRIPTION

The SSM2317 mini evaluation board is a small form factor

board (6.6 mm × 6.6 mm) with a pair of differential audio

input terminals (IN+ and IN−), a pair of audio signal output

terminals (OUT+ and OUT−), a ground terminal, and a VDD

terminal. It is designed for easy integration into the SSM2317

application board.

The SSM2317 mini evaluation board carries a complete

application circuit for driving a loudspeaker. Figure 1 shows

the top view of the evaluation board, and Figure 2 shows the

bottom view.

07824-001

Figure 1. SSM2317 Evaluation Board Top View

07824-002

Figure 2. SSM2317 Evaluation Board Bottom View

EVAL-SSM2317-MINI

Rev. 0 | Page 2 of 8

TABLE OF CONTENTS

Features .............................................................................................. 1

General Description ......................................................................... 1

Evaluation Board Description ......................................................... 1

Revision History ............................................................................... 2

Evaluation Board Hardware ............................................................ 3

Input and Output Configuration ................................................ 3

Component Selection................................................................... 3

PCB Layout Guidelines .................................................................4

Getting Started ...............................................................................4

Evaluation Board Schematic and Artwork .....................................5

Ordering Information .......................................................................8

Bill of Materials ..............................................................................8

Ordering Guide .............................................................................8

ESD Caution...................................................................................8

REVISION HISTORY

5/09—Revision 0: Initial Version

EVAL-SSM2317-MINI

Rev. 0 | Page 3 of 8

EVALUATION BOARD HARDWARE

INPUT AND OUTPUT CONFIGURATION

On the bottom side of the board, there are two pad terminals,

IN+ and IN−, as shown in Figure 5. They are used to feed the

audio signal into the board. The two output terminals, marked

OUT+ and OUT− in Figure 5, drive a loudspeaker whose

impedance should not be less than 4 Ω.

Although the SSM2317 does not require external LC output

filters to operate because it has a low noise modulation scheme,

if the speaker length is >10 cm, it is recommended to put a

ferrite bead (L1 and L2) near each output pin of the SSM2317 to

reduce electromagnetic interference (EMI), as shown in the

schematic in Figure 3. For optimal performance, as specified

in the SSM2317 data sheet (in particular, for THD and SNR),

remove the entire EMI filter, short across the ferrite bead

terminals, and open the capacitor terminals.

COMPONENT SELECTION

Selecting the right components is the key to achieving the

performance required at the budgeted cost.

ALC Threshold Setting Resistor—R3

The maximum output amplitude threshold (VTH) during the

limiting operation can be changed from 90% to 45% of VDD by

inserting an external resistor, RTH, between the VTH pin and

GND. Shorting the VTH pin to GND sets VTH to 90% of VDD.

Leaving the VTH pin unconnected sets VTH to 45% of VDD. The

relation of RTH to VTH is shown by the following equation:

TH V

V×

×+

×= 2kΩ50

kΩ50

9.0

Maximum output power is derived from VTH by the following

equation:

OUT R

2⎟

⎠

⎞

⎜

⎝

⎛

where RSP is the speaker impedance.

Input Coupling Capacitor Selection—C1 and C2

The input coupling capacitors, C1 and C2, should be large

enough to couple the low frequency components in the

incoming signal but small enough to filter out unnecessary

lower frequency signals. For music signals, the cutoff frequency

is, typically, between 20 Hz and 30 Hz.

The cutoff frequency is calculated by

C = 1/(2πRfc),

where:

R = 10 kΩ + Rext (the external resistor used to fine-tune the

desired gain; on the schematics (see Figure 3), this is the 0 Ω

resistor at the input pins).

fc is the cutoff frequency.

Output Ferrite Beads—L1 and L2

The L1 and L2 output beads are necessary components for

filtering out the EMI caused at the switching output nodes when

the length of the speaker wire is greater than 10 cm. The penalty

for using ferrite beads for EMI filtering is slightly worse noise

and distortion performance at the system level due to the non-

linearity of the beads. Make sure that these beads have enough

current conducting capability while providing sufficient EMI

attenuation.

The current rating needed for an 8 Ω load is about 420 mA.

Impedance for the beads at 100 MHz must be 220 Ω. In

addition, the lower the dc resistance (DCR) of the beads, the

better for minimizing their power consumption. Table 1 shows

the recommended beads.

Output Shunting Capacitors—C3 and C4

Two capacitors, C3 and C4, work with the L1 and L2 ferrite

beads. Use small size (0603 or 0402), multilayer ceramic

capacitors made from X7R or COG (NPO) materials.

Note that the capacitors can be used in pairs: a capacitor with

small capacitance (up to 100 pF) plus a capacitor with bigger

capacitance (1 nF). This configuration provides better EMI

reduction for the whole frequency spectrum. For BOM cost

reduction and capable performance, a single capacitor of

approximately 470 pF can be used.

Table 1. Recommended Beads

Part No. Manufacturer Z (Ω) IMAX (mA) DCR (Ω) Size (mm)

BLM18PG121SN1D Murata 120 2000 0.05 1.6 × 0.8 × 0.8

MPZ1608S101A TDK 100 3000 0.03 1.6 × 0.8 × 0.8

MPZ1608S221A TDK 220 2000 0.05 1.6 × 0.8 × 0.8

BLM18EG221SN1D Murata 220 2000 0.05 1.6 × 0.8 × 0.8

EVAL-SSM2317-MINI

Rev. 0 | Page 4 of 8

PCB LAYOUT GUIDELINES

To keep the EMI under the allowable limit and ensure that the

amplifier chip operates under the temperature limit, PCB layout

is critical in application design. The SSM2317 works well only if

the following techniques are implemented in the PCB design to

keep EMI and the amplifier temperature low.

Layer Stacks and Grounding

Use a 4-layer structure in the stack-up for the evaluation board,

as follows:

• Top layer—component layer with power and output copper

land and ground copper pouring.

• Second layer—dedicated ground plane.

• Third layer—dedicated power plane.

• Bottom layer—bottom layer with ground copper pouring.

Component Placement and Clearance

Place all related components except decoupling capacitors on

the same side as the SSM2317 to avoid vias and as close as

possible to the chip (see Figure 4).

Place the decoupling capacitors, C5 and C7, on the bottom side

as close as possible to the VDD and GND pins (see Figure 5).

Place the C3 and C4 capacitors and the R1 pull-up resistor on

the bottom layer (see Figure 5).

Traces and Solder Resist

All traces between adjacent pads must be covered with solder

resist. Traces should come symmetrically off the pads.

Use 5 mils traces at the SSM2317 pads to prevent the solder

from escaping.

Top Layer Copper Land and Ground Pouring

The output peak current of this amplifier is more than 1 A;

therefore, PCB traces should be wide (>2 mm) to handle high

current. For the best performance, use symmetrical copper

lands as large as space allows, instead of traces for output pins

(see Figure 3).

Pour ground copper on the top side and use many vias to

connect the top layer ground copper to the dedicated ground

plane. The copper pouring land on the top layer serves as both

the EMI shielding ground plane and the heat sink for the

SSM2317.

Power Land

Connect Pin B2 directly to Pin A2 by a 5 mil trace and make a

copper land for the power near A2. If space allows, use four

12/24 mil vias to connect the top layer power land to the

dedicated power plane (Layer 3).

GETTING STARTED

To ensure proper operation, carefully follow Step 1 through Step 3.

1. Connect the load to the audio output terminals, OUT+ and

OUT−.

2. Connect the audio input to the audio input terminals, IN+

and IN−.

3. Connect the power supply to VDD and GND.

EVAL-SSM2317-MINI

Rev. 0 | Page 5 of 8

EVALUATION BOARD SCHEMATIC AND ARTWORK

07824-003

IN+ OUT+

IN–

IN+

IN–

OUT+

OUT–

SD GND

ALC_EN

VTH

3A VDD

SSM2317

0.1µF

1nF

0.1µF

6.98kΩ

GAP

100kΩ

VDD

0.1µF

10µF

P1 P6

VDD

B0603

Figure 3. Schematic of the SSM2317-MINI Evaluation Board

EVAL-SSM2317-MINI

Rev. 0 | Page 6 of 8

07824-004

Figure 4. Top Layer with Top Silkscreen

07824-005

Figure 5. Bottom Layer with Bottom Silkscreen (Mirror Image)

07824-006

Figure 6. Top Silkscreen

07824-007

Figure 7. Top Layer

07824-008

Figure 8. Top Layer

07824-009

Figure 9. Layer 2 (Ground Plane)

EVAL-SSM2317-MINI

Rev. 0 | Page 7 of 8

07824-010

Figure 10. Layer 3 (Power Plane)

07824-011

Figure 11. Bottom Layer

7824-012

Figure 12. All Layer Silkscreen

EVAL-SSM2317-MINI

Rev. 0 | Page 8 of 8

ORDERING INFORMATION

BILL OF MATERIALS

Table 2.

Qty Reference Designator Description Supplier/Part No.

3 C1, C2, C7 Ceramic capacitor, 0.1 μF, 6.3 V Murata, GRM033R60J104KE19D

2 C3, C4 Ceramic capacitor, 1 nF, 10%, 5 V Kemet, C0603C102J5GACTU

1 C5 Ceramic capacitor, 10 μF, 10 V Murata, GRM31MF51A106ZA01L

1 G1 GAP N/A

2 L1,L2 Ferrite chip, B0603, 220 Ω, 2 A TDK, MPZ1608S221A

6 P1, P2, P3, P4, P5, P6 PAD1 N/A

2 R1, R2 Resistor, 100 kΩ Panasonic, ERJ-1GEF1003C

1 R3 Resistor, 6.98 kΩ Panasonic, ERJ-1GEF6981C

1 U1 SSM2317 Analog Devices, SSM2317

ORDERING GUIDE

Model Description

SSM2317-MINI-EVALZ1 Evaluation Board

1 Z = RoHS Compliant Part.

ESD CAUTION

registered trademarks are the property of their respective owners.

EB07824-0-5/09(0)