APA100 100−W Analog Input Class-D Amplifier TPA2001D1/TAS5111 User’s Guide August 2004 Audio Power Amplifiers SLOU170
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Information About Cautions and Warnings Preface Read This First About This Manual This user’s guide describes the characteristics, operation, and the use of the APA100 reference design board. It covers all pertinent areas involved to properly use this reference design board along with the devices that it supports. The physical PCB layout, schematic diagram, and circuit descriptions are included. This reference design demonstrates how to make the TPA2001D1 and TAS5111 into a 100-W class-D amplifier.
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Contents Contents 1 EVM Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Power Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Supply Voltage . . . . . . . . . . . . . . . . . . . . .
Contents Figures 1−1 1−2 2−1 2−2 2−3 2−4 2−5 3−1 4−1 4−2 4−3 4−4 4−5 4−6 4−7 4−8 4−9 5−1 5−2 5−3 5−4 5−5 5−6 5−7 5−8 5−9 THD+N vs Output Power (a), THD+N vs Frequency (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 APA100 EVM Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 APA100 Split Plane Top Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 1 EVM Overview This reference design demonstrates how to make the TPA2001D1 and the TAS5111 into a 100-W class-D amplifier. The user’s guide discusses how the TPA2001D1 is used as an analog input class-D modulator. The analog modulator is input to the TAS5111, which is an H-bridge that effectively extends the supply range from the TPA2001D1’s 3-V rails to 29.5 V with the TAS5111. The 18-V to 29.5-V power supply is applied across the power supply banana plugs J3 and J4. Apply 18 V to 29.
Features 1.1 Features This reference design or evaluation module (EVM) features the TPA2001D1, TAS5111, and TLV2464A. For simplicity, this EVM is referred to as the APA100 EVM to cover all parts that are supported in this user’s guide. The APA100 EVM is an evaluation module designed for a quick and easy way to evaluate the functionality and performance of the 100−W analog input class−D amplifier. The features of this amplifier follow. - Wide supply range of 18 V to 29.
EVM Basic Function/Block Diagram and NPN transistor circuit is used to create the 3-V supply for the TPA2001D1 and TLV2464A; therefore, the user only needs to apply the single-supply voltage. A+ supply is used for powering the TAS5111 and is input for the zener diode/NPN transistor circuit used to generate the 3-V supply for the TPA2001D1 and TLV2464A. To avoid potential damage to the EVM board, make sure that the correct cables are connected to their respective terminals as labeled on the EVM board.
EVM Basic Function/Block Diagram Figure 1−2.
Chapter 2 PCB Design This chapter gives layout guidelines for the APA100 reference design. Topic Page 2.1 PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2.2 Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6 2.3 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PCB Layout 2.1 PCB Layout The critical part of the design lies particularly in the layout process. The EVM layout should be followed exactly for optimal performance. The main concern is the placement of components and the proper routing of signals. Place the bypass/decoupling capacitors as close as possible to the pins; properly separate the linear and switching signals from each other. Because of its importance, carefully consider the ground plane in the layout process.
PCB Layout Figure 2−2. APA100 Split Plane Bottom Layout 2.1.2 H-Bridge Layout The H-bridge is laid out based on recommendations from the TAS5111 data sheet and follows the same pattern as the DAVREF100 EVM board. 1) Keep local decoupling and bootstrap capacitors and resistors close to pins. J Minimize trace length to C29, and use wide traces. J Local PVDD decoupling R35, C35, R36, and C36 traces should be as short and as wide as possible. 2) Use a ground plane.
PCB Layout 3) Use a split ground plane to keep high switching ground currents from the operational amplifier circuitry. 4) Place decoupling capacitors close to the TLV2464A and TPA2001D1 5) Place RC filter capacitors (C20, C23, and C24) close to the operational amplifier, with capacitor grounds connecting with a low−impedance path to the operational amplifier ground pin.
PCB Layout Figure 2−4. Bottom Copper and Silkscreen Figure 2−5. Drill Drawing 2.5 INCH 3.
Bill of Materials 2.2 Bill of Materials Table 2−1. Parts List Reference Qty Value Manufacturer Part Number Description 2 22 pF TDK C1608C0G1H220J 50 V, size 603, COG, 5% C13,19,20,R25 4 56 pF TDK C1608C0G1H560J 50 V, size 603, COG, 5% C6,9,11,12,14,17,18, 21,49,50 10 220 pF TDK C1608X7R1H221K 50 V, size 603, X7R, 10% C4,25 2 3300 pF TDK C1608C0G1H332J 50 V, size 603, COG, 5% C1,30,32,33, 35−37, 40, 42−46,48 16 0.
Schematic 2.
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Chapter 3 EVM Operation This chapter covers in detail the operation of the APA100 EVM to guide the user in evaluating the audio power amplifier and in interfacing the APA100 EVM to an audio input and power supply. Topic Page 3.1 Quick Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3.2 Power−Up/Down Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 3.3 Reset Button/Mute . . . . . . . . . . . . . . . .
Quick Start 3.1 Quick Start Follow these steps to use the APA100 EVM. APA100 audio input connection can be made via a phono jack (J1), or by soldering to its pins. The power supply and outputs can be connected with banana connectors or wires via screw terminals. Figure 3−1 shows numbered callouts for selected steps. Figure 3−1. Quick Start Module Map 6 2 5 4 Power Supply 1) Ensure that all external power sources are set to off. 2) Connect an external regulated power supply, set from 18 V to 29.
Power−Up/Down Sequence Power Up 6) Press and hold the RESET button (S1) 7) Verify correct voltage and input polarity, and set the external power supply to on. 8) Depress the RESET button (S1). The EVM begins operation. 9) Adjust the signal source level as needed. 10) Hold RESET button (S1) while powering down 3.2 Power−Up/Down Sequence The RESET pin of the TAS5111 needs to be held low while turning on power. This enables the feedback loop to get settled and avoids a loud pop.
Changing the Gain 3.5 Changing the Gain The APA100 EVM is set with a gain of 31.4 dB, but can be adjusted. The front-end has a gain of 4.4 dB (−1.667 V/V), and a back-end gain of 27 dB (−22.4 V/V), for a total of 31.4 dB (37.3 V/V). The back-end gain needs to be kept constant, because it is set by the control-loop feedback system with the TLV2464A, TPA2001D1, and TAS5111. The front-end gain is set by section A of the quad operational amplifier TLV2464A.
Chapter 4 Technical Information This chapter goes into the details of the design of the 100-W amplifier. The design comprises the modulator, H-bridge, operational amplifier, feedback loop, LC filter, and thermal. Topic Page 4.1 Feedback System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.2 TPA2001D1 (Class-D Modulator) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.3 TAS5111 (H-Bridge) . . . . . . . . . . . . . . . . . . . . . . . .
Feedback System Design 4.1 Feedback System Design The APA100 EVM uses feedback to lower distortion, increase supply ripple rejection, and make the gain not change with supply voltage. This section goes through the following steps to close the loop. 1) Take feedback at TAS5111 outputs before the LC filter, so that it is unneccary to cancel two poles of the LC filter. 2) Set corner, Fc, frequency to less than half the minimum switching frequency, Fsw.
Feedback System Design operational amplifier (R22, R23, C20, C23, and C24) was eventually reduced from 400 kHz to 252 kHz to optimize performance; compensation for this is discussed later. Notice that in Figure 4−8, the switching frequency of each output is 250 kHz, but the differential frequency is 500 kHz. The poles greater than 400−kHz from the low-pass filters do not affect the stability because they are ten times the corner frequency. The phase from a pole starts at the pole frequency divided by ten.
Feedback System Design Figure 4−3. Open− and Closed−Loop Frequency Response With TPA2001D1 Pole and Canceling Zero F Open Loop Gain P0 X 20 dB / Decade Gain − dB Closed Loop Gain Fc = 40 kHz F P0 0 Degrees X X X 80 kHz 10 >400 kHz Phase F P0* 10 −90 Degrees Frequency − Hz Now that the poles and zeros have been realized, the closed−loop gain can be set. First, calculate the open−loop gain by multiplying the gain (adding in dB) of each block, if there was no feedback.
Feedback System Design The closed−loop gain is set to 27 dB to allow enough gain from the 3−V signal to the A+ voltage range. This leaves sufficient low−frequency correction. Figure 4−4 shows the circuit used for the APA100 feedback. Equation (2) shows the closed−loop response. R20 R18 Closed−loop gain + 45 (2) Resistors R20 and R18 need to be set low to limit noise. Resistor R18 is set to 2000 Ω and R18 set to 1000 Ω for a closed−loop gain of 22.4 V/V.
Feedback System Design Instead of calculating the bandwidth, PSPICE was used with a linearized circuit (see Figure 4−5) to simulate and adjust the component values to approximately 40-kHz bandwidth. Then, Equations 7 and 8 were used to set the poles and zeros.
TPA2001D1 (Class-D Modulator) Figure 4−6. PSPICE Simulation of Open−Loop Response 200 Phase (5) 100 −0 TAS5111 Output (dB) Integrator Output (dB) −100 −200 −300 100 1k 100 k 10 k f − Frequency − Hz 1M 4.2 TPA2001D1 (Class-D Modulator) The TPA2001D1 was chosen as an excellent performance, low-cost analog class-D modulator. A class-D modulator takes an analog input signal and outputs a pulse width modulated (PWM) signal.
TPA2001D1 (Class-D Modulator) Figure 4−7. TPA2001D1 Block Diagram VDD AGND VDD Pre-Amp Integrator Comparator PVDD INN _ Gain Adj. Rs2 Cint2 + _ Deglitch Logic Gate Drive OUTN + _ PGND + _ cmv + + INP PVDD _ Gain Adj.
TAS5111 (H-Bridge) For more information concerning the TPA2001D1 operation and modulation scheme, see the TPA2001D1 data sheet http://focus.ti.com/docs/prod/folders/print/tpa2001d1.html 4.3 TAS5111 (H-Bridge) The TAS5111 converts the PWM signal from the 3-V peak-to-peak outputs of the TPA2001D1 to 18-V to 29.5-V peak-to-peak. This allows the output power to increase from 1 W with just the TPA2001D1 to 100 W with the TAS5111 H-bridge. The TAS5111 has short-circuit and thermal protection.
LC Filter 4.5 LC Filter The LC filter serves two purposes in this design. 1) Reduces EMI 2) Enables overcurrent (OC) protection. The outputs of the TAS5111 are square waves with fast rise and fall times. The square waves produce harmonics up to 500 MHz. The speaker wire makes transmission lines for these frequencies. The LC filter attenuates the high frequencies that are transmitted over the speaker wires and increase EMI. The LC filter is shown in Figure 4−9. Figure 4−9.
Thermal 4.6 Thermal The APA100 thermal issues lie with the TAS5111. The following thermal calculations and tables are taken from the TAS5111 data sheet. The TAS5111 is designed to be interfaced directly to a heatsink using a thermal interface compound (for example, Wakefield Engineering type 126 thermal grease.) The heatsink then absorbs heat from the ICs and couples it to the local air.
Thermal As an indication of the importance of keeping the thermal grease layer thin, if the thermal grease layer increases to 0.002 inch thick, the required heatsink thermal resistance changes to 2.4°C/W. The large heatsink used for the APA100 EVM is required for full output power sine waves over temperature. A smaller heatsink can be used for music, which requires much less average power. The heatsink should be tight without bending the board or damaging the IC.
Chapter 5 Measured Results This chapter shows the performance of the APA100 reference design. An Audio Precision analyzer was used to produce the graphs in this chapter. Topic Page 5.1 Total Harmonic Distortion + Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 5.2 Output Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 5.3 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Total Harmonic Distortion + Noise 5.1 Total Harmonic Distortion + Noise The APA100 has excellent total harmonic distortion + noise (THD+N). Figure 5−1 and Figure 5−2 show the THD+N versus frequency, and Figure 5−3 and Figure 5−4 show THD+N vs output power. A 30-kHz bandwidth limit was used on the audio precision to limit switching frequency from affecting the measurement. Figure 5−1. APA100 THD+N vs Frequency With 4-W Load THD+N − Total Harmonic Distortion + Noise − % 100 VCC = 29.
Total Harmonic Distortion + Noise Figure 5−3. APA100 THD+N vs Output Power With 4-W Load THD+N − Total Harmonic Distortion + Noise − % 20 5 f = 1 kHz, PVDD = 15 V, 18 V, 20 V, 24 V, 28 V, 29.5 V 1 0.5 0.1 0.05 0.01 10 m 1 2 10 20 PO − Output Power − W 100 200 Figure 5−4. APA100 THD+N vs Output Power With 8-W Load THD+N − Total Harmonic Distortion + Noise − % 20 5 f = 1 kHz, PVDD = 15 V, 18 V, 20 V, 24 V, 28 V, 29.5 V 1 0.5 0.1 0.05 0.
Output Power 5.2 Output Power The APA100 can output over 100 W into 4 Ω. The curves in Figure 5−5 and Figure 5−6 show the output power versus supply voltage. Figure 5−5. APA100 Output Power vs Supply Voltage With 4-W Load 120 f = 1 kHz PO − Output Power − W 100 PO @ 10% THD 80 60 PO @ 1% THD 40 20 0 18 20 22 24 26 VCC − Supply Voltage − V 28 Figure 5−6.
Efficiency 5.3 Efficiency The APA100 is a highly efficient class-D audio power amplifier. The efficiency is greater than 85% efficient with 4- or 8-Ω load. The efficiency plot is shown in Figure 5−7. Figure 5−7.
Gain and Phase Response 5.4 Gain and Phase Response The APA100 is a closed−loop, class-D audio power amplifier with an LC output filter. The output filter and the 39-kHz loop bandwidth limit the bandwidth of the APA100 reference design. The gain versus frequency curve is shown in Figure 5−8. The 4-Ω curve rolls off sooner than the 8-Ω curve. Figure 5−8. APA100 Gain vs Frequency With 4-W and 8-W Load 40 8 35 Gain − dB 30 4 25 20 15 10 5 0 20 100 200 1k 2k 10 k 20 k f − Frequency − Hz 5.
Supply Ripple Rejection 5.6 Supply Ripple Rejection The APA100 uses a closed loop which keeps the gain from changing with supply voltage and improves the supply ripple rejection ratio (kSRR) over an open−loop class-D amplifier. The supply ripple rejection ratio versus frequency curve is shown in Figure 5−9. Figure 5−9.
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