ST AN3383 APPLICATION NOTE

AN3383

Application note

STA350BW 2.0-channel demonstration board

Introduction

The purpose of this application note is to describe:

■how to connect the STA350BW 2.0-channel demonstration board

■how to evaluate the demonstration board performance with all the electrical curves

■how to avoid critical issues in the PCB schematic and layout of the the STA350BW

The STA350BW demonstration board is specifically configured for 2.0 BTL channels, releasing up to 2 x 50 W into 6 ohm of power output at 25 V of supply voltage using reduced components. It is a complete solution for the digital audio power amplifier.

Figure 1. STA350BW 2.0-channel demonstration board

Connected with AP WLink board (I2C & I2S)

Speaker Output

L CH

Speaker Output

R CH

VCC

DC 4.5-26V

AM045230v1

April 2011

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www.st.com

Contents	AN3383

Contents

1	Functional description of the demonstration board . . . . . . . . . . . . . .		. 4
	1.1	Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
	1.2	Output configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
	1.3	Schematic and block diagrams, PCB layout, bill of material . . . . . . . . . . . .	5
2	Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9
3	Thermal test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		14
4	Design guidelines for schematic and PCB layout . . . . . . . . . . . . . . . .		16
	4.1	Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	16

4.1.1 Main driver for selection of components . . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.2 Decoupling capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.1.3 Output filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4.2 PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5

Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

28

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AN3383	List of figures

List of figures

Figure 1. STA350BW 2.0-channel demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Figure 2. Schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 3. Block diagram of test connections with equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 4. Top view of PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 5. Bottom view of PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Figure 6. Efficiency (2 channels, BTL configuration), VCC = 26 V, RL = 6 ohm . . . . . . . . . . . . . . . . . . 9 Figure 7. Efficiency (2 channels, BTL configuration), VCC = 26 V, RL = 8 ohm . . . . . . . . . . . . . . . . . 10

Figure 8. Output power vs. supply voltage, RL = 6 ohm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 9. Output power vs. supply voltage, RL = 8 ohm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 10. Frequency response, VCC = 24 V, RL = 6 ohm, 0 dB (Pout = 1 W) . . . . . . . . . . . . . . . . . . 11 Figure 11. Crosstalk, VCC = 24 V, RL = 6 ohm, 0 dB (Pout = 1 W) . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 12. SNR, VCC = 24 V, RL = 6 ohm, 0 dB (Pout = 1 W) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 13. THD vs. frequency, VCC = 24 V, RL = 6 ohm, Pout = 1 W . . . . . . . . . . . . . . . . . . . . . . . . . 12 Figure 14. FFT (0 dBFS), VCC = 24 V, RL = 6 ohm, 0 dBFS (Pout = 1 W) . . . . . . . . . . . . . . . . . . . . . 13 Figure 15. FFT (-60 dBFS), VCC = 24 V, RL = 6 ohm, 0 dBFS (Pout = 1 W) . . . . . . . . . . . . . . . . . . . . 13 Figure 16. THD vs. output power, VCC = 24 V, RL = 6 ohm, f = 1 kHz . . . . . . . . . . . . . . . . . . . . . . . . 13 Figure 17. Output power = 2 x 5 W, VCC = 26 V, load = 6 ohm, frequency = 1 kHz . . . . . . . . . . . . . . 14 Figure 18. Output power = 2 x 10 W, VCC = 26 V, load = 6 ohm, frequency = 1 kHz . . . . . . . . . . . . . 14 Figure 19. Output power = 2 x 15 W, VCC = 26 V, load = 6 ohm, frequency = 1 kHz . . . . . . . . . . . . . 15 Figure 20. Output power = 2 x 38 W, VCC = 26 V, load = 8 ohm, frequency = 1 kHz . . . . . . . . . . . . . 15 Figure 21. Output filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 22. Power dissipated over the series resistance [P = C*f*(2*V)2]. . . . . . . . . . . . . . . . . . . . . . . 17 Figure 23. Power dissipated over the series resistance [P = C*f*2(V2)] . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 24. Damping network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 25. Main filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 26. Recommended power-up and power-down sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 27. Snubber network soldered as close as possible to the related IC pin . . . . . . . . . . . . . . . . 19 Figure 28. Electrolytic capacitor used first to separate the VCC branches . . . . . . . . . . . . . . . . . . . . . . 20 Figure 29. Path between VCC and ground pin minimized in order to avoid inductive paths . . . . . . . . 20 Figure 30. Large ground planes on the top and bottom sides of the PCB . . . . . . . . . . . . . . . . . . . . . . 21 Figure 31. PLL filter soldered as close as possible to the FILT pin . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure 32. Symmetrical paths created for output stage (for differential applications) . . . . . . . . . . . . . 22 Figure 33. Coils separated in order to avoid crosstalk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 34. VCC filter for high frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Figure 35. Decoupling capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 36. Snubber filter for spike high frequency in PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 37. Correct common-mode and differential snubber placement . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 38. Correct output routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 39. Comparison of output routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Figure 40. Thermal layout with large ground (1/3 for top and bottom layers) . . . . . . . . . . . . . . . . . . . 26 Figure 41. Thermal layout with large ground (2/3 for thermal and soldering holes). . . . . . . . . . . . . . . 26 Figure 42. Comparison of thermal layout (top layer) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Figure 43. Comparison of thermal layout (bottom layer) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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Functional description of the demonstration board	AN3383

1 Functional description of the demonstration board

The following terms used in this application note are defined as follows:

●THD+N vs. Freq: Total harmonic distortion plus noise versus frequency curve

●THD+N vs. Pout: Total Harmonic Distortion (THD) plus noise versus output power

●S/N ratio: Signal-to-noise ratio

●FFT: Fast Fourier Transform Algorithm (method)

●CT: Channel separation L to R, or R to L channel crosstalk

	The equipment used includes the following:
	●	Audio Precision (System 2700) by AP Co., USA)
	●	DC power supply (4.5 V to 26 V)
	●	Digital oscilloscope (TDS3034B by Tektronix)
	●	PC (with APWorkbench GUI control software installed)
1.1	Connections
	Power supply signal and interface connection
	1.	Connect the positive voltage of 24V DC power supply to the +Vcc pin and negative to
		GND.
	2.	Connect the APWorkbench board to the J1 connector of the STA350BW demonstration
		board.
	3.	Connect the S/PDIF signal cable to the RCA jack on the APWLink board, connecting to
		the signal source such as Audio precision or DVD player.
Note:	The voltage range of the DC power supply for VCC is 4.5 V to 26 V.
1.2	Output configuration
	The STA350BW demo board is specifically configured in 2 BTL channels. For the software
	setup, please refer to the APWUserManualR1.0.pdf.

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1.3Schematic and block diagrams, PCB layout, bill of material

Figure 2. Schematic diagram

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Figure 3. Block diagram of test connections with equipment

Audio Precision Equipment

									Monitor
	Output				S/PDIF
	to AP				Signal				Digital Oscilloscope
									TDS3034B Tektronix
									APWLink Board
					I2S Input
		STA350BW
					(DC3V3)
		Demo B’D
							(DC7V)
									PC with GUI to control the
					DC Power Supply				chipset
	From 4.5V to26V

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Figure 4.	Top view of PCB layout

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Figure 5. Bottom view of PCB layout

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	Functional description of the demonstration board							AN3383
	Table 1.		Bill of material
	No.		Type	Footprint	Description	Qty	Reference	Manufacturer
	1		Jack	Through-hole	4P Speaker Jack	1	J7	Any source
	2		MCAP	Through-hole	680NF-M(63V) Capacitor	2	C415SL, C416S	Any source
	3	Terminal		Through-hole	2P Pitch: 5 mm Connector Terminal	1	CN2	Phoenix
								Contact
	4		CNN	Through-hole	16P (8 x 2 row) 2.5 mm male CNN	1	J1	Any source
	5		CCAP	CAP0603	50 volt NPO 330 pF +/- 10%	2	C418A, C425	Murata
	6		CCAP	CAP0603	50 volt NPO 680 pF +/- 10%	1	C9	Murata
	7		CCAP	CAP0603	50 volt 1 nF +/- 10%	1	C3	Murata
	8		CCAP	CAP0603	50 volt 4.7 nF +/- 10%	1	C7	Murata
							C2, C4, C5, C11,
							C15, C421A,
							C421B, C422A,
	9		CCAP	CAP0603	50 volt 100 nF +/- 10%	15	C422B, C423A,	Murata
							C423B, C424A,
							C424B, C427A,
							C427B
	10		CCAP	CAP1206	50 volt 1 µF +/-10%	2	C426A, C426B	Murata
	11		RES	R1206	4R7, +/-5% 1/4W	4	R424A, R424B,	Murata
							R425A, R425B
	12		RES	R1206	20 +/-5% 1/4W	2	R422A, R423	Murata
	13		RES	R0603	0 ohm 1/16W	1	R31	Murata
	14		RES	R0603	2R2 +/-5% 1/16W	1	R32	Murata
	15		RES	R0603	10K +/-5% 1/16W	1	R1	Murata
	16		RES	R0603	2.2K +/-5% 1/16W	1	R6	Murata
	17		RES	R0603	NS	2	R4, R5
	18		ECAP	Through-hole	22 µF/ 16 V	1	C12	Rubycon/
								Panasonic
	19		ECAP	Through-hole	1000 µF / 35 V 105 Centigrade	1	C428	Rubycon/
								Panasonic
	20	Plastic rod			Hexagonal rod 15 mm length,	4	Four Corner
					male type
	21	Plastic rod			Hexagonal rod 8 mm length,	4	Four Corner
					female type
	22		IC	PSSO36	STA350BW	1	IC1	ST
	23		Coil	Through-hole	15 µH Choke Coil (1014P-01-150L)	4	L421A, L421B,	KwangSung
							L422A, L422B
	24		PCB		STA350BW 2.0 CH VER1.0	1		Fastprint

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AN3383	Test results

2 Test results

All the results and graphs are from measures using equipment from Audio Precision.

Figure 6. Efficiency (2 channels, BTL configuration), VCC = 26 V, RL = 6 ohm
+1
+0.9
+0.8
+0.7
+0.6
+0.5
+0.4
+0.3
+0.2
+0.1
+0	10	15	20	25	30	35	40	45	50	55
5
					W
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