Reference Design for a Class-D

Abstract: This reference design demonstrates the use of the MAX9736 Class D audio amplifier in a stereo audio, docking station application. The MAX9736 2.1 demo box is a complete powered speaker dock that uses two MAX9736 ICs to drive a 3-channel speaker system consisting of two 2in satellite speakers and one 5in subwoofer. The reference design is intended to be used with a portable audio player as its main music source. The overall solution size is very compact and features active equalization, power-supply monitoring, and dynamic equalization for the subwoofer.

Important Design Features

• Compact all-in-one design
• Operates from a single 12V to 20V DC power supply
• High SPL output from a small box
• High-efficiency Class-D design
• Active EQ, including dynamic bass equalization
• Excellent sound quality from cost-effective drivers

Bill of Materials

Designator	Qty	Description
C1	1	470μF ±20% 25V aluminum electrolytic capacitor Panasonic? EEU-FM1E471
C2, C12, C310	3	0.1μF ±10% 50V X7R ceramic capacitor (0603) Murata? GRM188R71H104K TDK C1608X7R1H104K
C321	1	1μF (0603)
C16	1	10μF (1206)
C106, C109–111, C114, C206, C209–211, C214	10	NS (0603)
C3–5	3	0.1μF ±10% 16V X7R ceramic capacitor (0603) Murata GRM188R71C104K TDK C1608X7R1C104K
C13	1	0.1μF (0603)
C316–317	2	0.1μF (0805)
C303	1	0.33μF (0603)
C302	1	0.47μF (0603)
C305, C307	2	100nF (0603)
C103–104, C203–204, C301	5	100pF (0603)
C121, C220–221, C120, C314–315	6	100pF (0603)
C117–119, C217–219	6	10nF (0603)
C107, C207	2	150pF (0603)
C306, C308	2	15nF (0603)
C6–10, C15, C313, C318–320	10	1μF ±10% 16V X7R ceramic capacitor (0603) Murata GRM188R71C105K TDK C1608X7R1C105K
C312, C14, C311	3	1μF (0603)
C216, C116	2	1μF (0805)
C100–101, C200–201	4	2.2μF (0805)
C304	1	2.2μF (0805)
C102, C108, C112, C115, C202, C215, C300	7	33pF (0603)
C208, C212	2	33pF (0603)
C322	1	33pF (0603)
C113, C213	2	4.7nF (0603)
C105, C205	2	68nF (0603)
C11, C309	2	220μF ±20% 35V aluminum electrolytic capacitor (10mm x 12.5mm) Panasonic EEUFM1V221
J30	1	4-pin header HIROSE DF3A-4P
U7	1	Opto-FET (DIP6-SMT) Fairchild? H11F1SM
L100–101, L200–201, L300–301	6	Ferrite bead (1206)
FB1	1	Ferrite bead (1206)
J3	1	6-pin header
J10, J20	2	2-pin header HIROSE DF3A-2P
J2	1	RCA? dual jack PCB mount
D1	1	LED red (0603)
D5	1	LED blue (0603)
Q2	1	Transistor NPN (SOT23) Fairchild MMBT3904
X1–2	2	Connector, screw mount
R7	1	Potentiometer 100K SMT
R303	1	Potentiometer 20K SMT
J1	1	Power jack, right angle Switchcraft? 722RA
R1	1	10kΩ ±5% resistor (0805)
R110, R210	2	NS resistor (0603)
R111, R211	2	10.5kΩ ±5% resistor (0603)
R100, R200	2	100Ω ±5% resistor (0603)
R10	1	100kΩ ±1% resistor (0603)
R106, R108, R206, R208	4	10kΩ ±5% resistor (0603)
R300–301	2	10kΩ ±5% resistor (0603)
R2–3	2	10kΩ ±1% resistor (0603)
R113, R213	2	11kΩ ±5% resistor (0603)
R309, R311–312, R314	4	11kΩ ±5% resistor (0603)
R306	1	12kΩ ±5% resistor (0603)
R114, R214	2	137kΩ ±5% resistor (0603)
R305	1	14.7kΩ ±5% resistor (0603)
R112, R212	2	150Ω ±5% resistor (0603)
R317	1	1kΩ ±5% resistor (0603)
R107, R109, R207, R209	4	1MΩ ±5% resistor (0603)
R8–9, R315–316	4	2.2kΩ ±5% resistor (0603)
R101–102, R201–202	4	20kΩ ±5% resistor (0603)
R5	1	220Ω ±5% resistor (0603)
R310, R313	2	24.3kΩ ±5% resistor (0603)
R302	1	2kΩ ±5% resistor (0603)
R308	1	3.24kΩ ±5% resistor (0603)
R307	1	3.3kΩ ±5% resistor (0603)
R115, R215	2	30.1kΩ ±5% resistor (0603)
R4	1	4.22kΩ ±1% resistor (0603)
R103–104, R203–204	4	40kΩ ±5% resistor (0603)
R304	1	7.15kΩ ±5% resistor (0603)
R105, R205	2	0Ω resistor (0603)
D6	1	Diode, dual, common-cathode (SOT-23-3) Fairchild MMBD4148CC
D2–3	2	Zener diode 4.3V, 20mA (SOT-23) Central CMPZ5229B
SPK1, SPK2	2	2in full-range loudspeaker Tymphany? 830970
SPK3	1	5.25in subwoofer loudspeaker Tymphany 830945
U1	1	Maxim? MAX9736BETJ+ (7mm x 7mm, 32-pin TQFN)