ANALOG DEVICES UG-192 Service Manual

Evaluation Board User Guide

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UG-192

Evaluation Board for SSM2317 Filterless Class-D Audio Amplifier

PACKAGE CONTENTS

SSM2317-EVALZ

OTHER SUPPORTING DOCUMENTATION

SSM2317 data sheet

GENERAL DESCRIPTION

The SSM2317 is a fully integrated, single-chip, mono Class-D audio
amplifier that 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 3 W of continuous output power with less
than 1% THD + N driving a 3  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.

Automatic level control (ALC) can be activated to suppress
clipping and improve dynamic range. This feature only requires
one external resistor tied to GND via the VTH pin and an
activation voltage on the ALC_EN pin. For setup configuration
and sync operation, see the SSM2317 data sheet.

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. 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 user guide describes how to configure and use the SSM2317
evaluation board to evaluate 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 OVERVIEW

The SSM2317 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.

Figure 1. SSM2317 Evaluation Board Top View

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS.

09354-001

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Figure 2. SSM2317 Evaluation Board Bottom View

09354-002

UG-192 Evaluation Board User Guide

TABLE OF CONTENTS

Package Contents.............................................................................. 1

Other Supporting Documentation................................................. 1

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

Evaluation Board Overview ............................................................1

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

Setting Up the Evaluation Board .................................................... 3

Input Configuration..................................................................... 3

Operation Mode Configuration ................................................. 3

REVISION HISTORY

10/10—Revision 0: Initial Version

Output Configuration...................................................................3

Power Supply Configuration .......................................................3

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

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

What to Test...................................................................................4

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

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

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

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Evaluation Board User Guide UG-192

+

SETTING UP THE EVALUATION BOARD

INPUT CONFIGURATION

A 4-pin header (J1) on the middle left side of the board feeds the
audio signal into the board (see Figure 1). If the input audio signal
is differential (IN+ and IN−), three pins of J1 are used for IN+,
IN−, and signal ground. For a single-ended audio input, only two
pins of J1 are used. One is for the signal ground and the other is
for either IN+ or IN−. If IN+ is used, place a jumper between
Pin 3 and Pin 4 of J1, shorting IN− to ground. If IN− is used,
place the jumper between Pin 1 and Pin 2 of J1, connecting IN+
to ground.

OPERATION MODE CONFIGURATION

The 6-pin header, J2, is used to turn on/off the SSM2317 amp­lifier and configure the ALC operation modes. Placing a jumper
across Pin 1 and Pin 2 of J2 shuts down the SSM2317 so that only
a minimum current (about 20 nA) is drawn from the power supply
(when R3 is shorted). Removing the jumper puts the SSM2317 in
normal operation. Placing a jumper across Pin 3 and Pin 4 of J2
disables ALC mode, while removing the jumper activates ALC
mode. When ALC is disabled, the SSM2317 behaves like a tradi­tional amplifier with a fixed 18 dB. Placing a jumper across Pin 5
and Pin 6 of J2 shorts across the ALC threshold resistor (on
board) and sets a maximum limiter level of 90% of V

(when

DD

ALC is activated).

OUTPUT CONFIGURATION

The output connector, J4, is located on the right side of the board
(see Figure 1). J4 drives a loudspeaker whose impedance should
be no less than 3 .

Although the SSM2317 does not require any external LC output
filters due to 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. Some users may
want to replace the ferrite beads with these inductors to evaluate
applications with specific EMI vs. audio performance constraints. As
an aid, a properly tuned ferrite bead-based EMI filter is assembled at
the output terminals of the device.

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.

POWER SUPPLY CONFIGURATION

The evaluation board schematic is shown in Figure 3. The 2-pin
header, J3, must be used to power the board. Care must be taken
to connect the dc power with correct polarity and voltage. The
positive voltage terminal of J3 (VDD) is indicated with an arrow
in Figure 1.

Polarity and Voltage

The wrong power supply polarity or an overvoltage may damage
the board permanently. The maximum peak current is approxi­mately 0.33 A when driving an 8 Ω load and when the input
voltage is 5 V.

COMPONENT SELECTION

Selecting the proper components is the key to achieving the
performance required at the cost budgeted.

ALC Threshold Setting Resistor—R5

When ALC mode is active, the maximum output amplitude
threshold (V
from 90% to 45% of V
between the VTH pin and GND. Shorting the VTH pin to GND
sets V

TH

V

to 45% of VDD. The relation of RTH to VTH is shown by the

TH

following equation:

V ×

TH

Maximum output power is derived from V
equation:

P

OUT

R

where

To tune a variety of V
the evaluation board. To measure the potentiometer resistance set­ting, insert an ohmmeter across Pin 5 and Pin 6 of J2.

Note that measuring the resistance across the potentiometer is not
adequate to determine the actual R
internal input resistance of 50 k at the VTH pin. The user must
take into account the internal resistance while evaluating actual
R

. For example, after tuning R5 to a desirable level, the user

TH

measures the resistance from Pin 5 and Pin 6 of J2. Then, to infer
the actual R

where:

R

Threshold

to GND.

R

Measured

) during the limiting operation can be adjusted

TH

by inserting an external resistor, RTH,

DD

to 90% of VDD. Leaving the VTH pin unconnected sets

R

k50

TH

×=

9.0

V

⎛

TH

⎜

2

⎝

=

R

SP

is the speaker impedance.

SP

, use this simple calculation:

TH

RR

2k50

2

⎞
⎟

⎠

levels, a potentiometer, R5, is mounted on

TH

−=

MeasuredThreshold

V

DD

R

×+

TH

by the following

TH

value. This is due to the

TH

111

k50

is the desired external resistor value from the VTH pin

is the measured resistance from the VTH pin to GND.

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