LM4962TLBD/NOPB

User's Guide SNAA027A – April 2006 – Revised May 2013 AN-1441 LM4962 Evaluation Board 1 Introduction The LM4962 Evaluation Board is designed to evaluate both mono and stereo applications. The LM4962 integrates a switching boost converter with an audio power amplifier. For stereo applications an external audio amplifier is needed. The LM4962 Evaluation Board presents the LM4962 along with the LM4951 audio power amplifier. For more information on the LM4962 or LM4951, see the device-specific data sheet. The LM4962 is an audio power amplifier primarily designed for driving ceramic speaker in cell phones, Smart Phones, PDA’s and other portable applications. It is capable of driving 15Vpp (typ) BTL, per channel, to a 2 μF + 30 Ω load with less than 1% THD + N from a 3.2VDC power supply. The LM4962 features a low power consumption shutdown mode, an internal thermal shutdown protection mechanism, over current protection (OCP) and over voltage protection (OVP). 2 Operating Conditions • Temperature Range -40°C ≤ TA ≤ +85°C • Boost Converter Supply Voltage (VDD) 3.0V < VDD < 5.0V • Amplifier Supply Voltage 2.7V < VAMP < 8.5V All trademarks are the property of their respective owners. SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback AN-1441 LM4962 Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 1 Demo Board Schematic 3 www.ti.com Demo Board Schematic D2 L1 J8 V1=1.23(1+R2/R3) Vdd R3 Cs1 Vdd SW C3 C2 R2 FB GND (sw) R5 Soft-Start Css SW-Leak VDD Bootstrap RPU4 OC/OV Detect Flagout J10 Rs LM4962 Cf3 Vamp Cs2 J3 Vdd R PU Rf3 SD Boost Vdd J5 RPU2 Cs3 GND SD Amp J6 Vo1 CinB RinB Bypass Vin Cb1 Vo1 Rchg1 CinA J7 Rchg2 OUTB J2 Cchg J1 Vo1 Cchg Vo2 OUTA Bypass Rb2 Vo2 RinA Vin LM4951 VDD RPU3 BW1 BW2 Shutdown J4 Rf2 Rf1 Cf1 Figure 1. Demo Board Schematic Table 1. Demo Board Connections Designator Label J1 IN A J2 OUTA J3 SD Boost Boost Converter Shutdown J3 open = Shutdown J3 shorted = Active J4 SD AmpB Amplifier B Shutdown (LM4951) J4 open = Shutdown J4 shorted = Active J5 SD AmpA Amplifier A Shutdown (LM4962) J5 open = Shutdown J5 shorted = Active J6 IN B J7 OUTB J8 GND VDD J9 J10 2 Function Single Ended Audio Input Signal A (LM4962) BTL Audio Output Signal A (LM4962) Single Ended Audio Input Signal B (LM4951) BTL Audio Output Signal B (LM4951) Power Supply Connection Stereo/Mono select J9 Shorted = Stereo J9 Open = Mono Flagout Flagout pin to monitor Over Voltage or Over Current conditions AN-1441 LM4962 Evaluation Board SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Start-Up Sequence www.ti.com 4 Start-Up Sequence For the LM4962 correct start-up sequencing is important for optimal device performance. Using the correct start up sequence will improve click/pop performance as well as avoid transients that could reduce battery life. For ringer/loudspeaker mode, the supply voltage should be applied first and both the boost and the amplifier should be in shutdown (J3 and J5 open). Then the boost converter can be activated (J3 shorted) followed by the amplifier (J5 shorted). If the boost converter shutdown is toggled while the amplifier is active an audible pop will be heard. 5 Setting the Output Voltage (V1) of Boost Converter The output voltage is set using the external resistors R2 and R5 (see Figure 1). A value of approximately 25 kΩ is recommended for R2 to establish the open loop gain of the boost converter. The output voltage of the boost converter can be calculated using Equation 1. V1 = VFB [1 + (R2 / R5)] 6 (1) Feed-Forward Compensation For Boost Converter Although the LM4962’s internal Boost converter is internally compensated, an external feed-forward capacitor, Cf, is required for stability (see Figure 1). Adding this capacitor puts a zero in the loop response of the converter. The recommended frequency for the zero's –3dB point should be approximately 60 kHz. C3 can be calculated using the formula in Equation 2. C3 = 1 / (2π x R2 x fz) 7 (2) PCB Layout Guidelines High frequency boost converters require very careful layout of components in order to get stable operation and low noise. All components must be as close as possible to the LM4962 device. It is recommended that a 4-layer PCB be used so that internal ground planes are available. See Figure 1 for demo board reference schematic and layout. Some additional guidelines to be observed: • Keep the path between L1, D2, and C2 extremely short. Parasitic trace inductance in series with D2 and C2 will increase noise and ringing. • If internal ground planes are available (recommended) use vias to connect directly to ground at the GND (SW) and GND pins of U1, as well as the negative sides of capacitors Cs1 and C2 • To ensure correct operation of this device, it is essential that the GND (SW) pin (A3), GND pin (D1), and the negative side of Cs2 be connected to the same GND plane. Cs2 should be placed as close as possible to these two GND planes 8 General Layout Recommendations This section provides practical guidelines for PCB layouts. Designers should note that these are only "ruleof-thumb" recommendations and the actual results will depend heavily on the final layout. 8.1 Power and Ground Circuits For multi-layer boards, it is important to isolate the switching power and ground trace paths from the amplifier power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central point rather than daisy chaining traces together in a serial manner) can have a major impact on low level signal performance. Star trace routing refers to using individual traces to feed power and ground to each circuit or even device. This technique requires a greater amount of design time but will not increase the final price of the board. 8.2 Avoiding Typical Design and Layout Problems Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB layer. When traces must cross over each other do it at 90°. Running digital and analog traces at 90° to each other from the top to the bottom side as much as possible will minimize capacitive noise coupling and crosstalk. SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback AN-1441 LM4962 Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 3 PCB Layout www.ti.com Table 2. LM4962 Evaluation Board Bill of Materials 9 Item Description Package U1 Ceramic Speaker Driver DSBGA U2 Audio Power Amplifier DSBGA Cf1, Cf3 Ceramic Capacitor 1210 Value Notes 82 pF, 50V 50V 50V C3 Ceramic Capacitor 1210 100 pF, 50V CinA, CinB Ceramic Capacitor 1210 0.39 μF, 50V C2, Cs1, Cs2, Cs3 Ceramic Capacitor 1210 4.7 μF, 16V Css Ceramic Capacitor 1210 10 nF, 16V Cb1, Cb2 Tantalum Capacitor 1210 1 μF, 16V D2 Schottky Diode SOD-123 20V, 0.5A On Semi MBR0520 L1 Inductor 4.3mm X 4.8mm X 3.5mm 10 μH, 1.04A Sumida CR43–100 R3 Resistor 0603 1.6 kΩ 1/10W, 5% R2 Resistor 0603 25 kΩ 1/10W, 5% Rpu, Rpu2, Rpu3, Rchg1, Rchg2, Resistor 0603 1 kΩ 1/10W, 5% low ESR, ESR < 50 Ω Rpu4 Resistor 0603 100 kΩ 1/10W, 5% RinA, RinB, Rf2 Resistor 0603 20 kΩ 1/10W, 5% Rf1, Rf3 Resistor 0603 200 kΩ 1/10W, 5% Rchg1, Rchg2 Resistor 0603 1 kΩ 1/10W, 5% R4 Resistor 0603 4.9 kΩ 1/10W, 5% R3 Resistor 0603 100 mΩ 1/10W, 5% PCB Layout Figure 2. Top Layer (Shown With Top Silkscreen visible) 4 AN-1441 LM4962 Evaluation Board SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated PCB Layout www.ti.com Figure 3. Mid Layer 1 (Shown With Top Silkscreen visible) Figure 4. Mid Layer 2 (Shown With Top Silkscreen visible) SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback AN-1441 LM4962 Evaluation Board Copyright © 2006–2013, Texas Instruments Incorporated 5 PCB Layout www.ti.com Figure 5. Bottom Layer (Shown With Top Silkscreen visible) Figure 6. Top Silkscreen 6 AN-1441 LM4962 Evaluation Board SNAA027A – April 2006 – Revised May 2013 Submit Documentation Feedback Copyright © 2006–2013, Texas Instruments Incorporated Revision Table www.ti.com 10 Revision Table Rev Date Description 0.1 04/20/06 Initial release. 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