LM48820

LM48820 Ground-Referenced, Ultra Low Noise, Fixed Gain, 95mW Stereo Headphone Amplifier June 2007 LM48820 Ground-Referenced, Ultra Low Noise, Fixed Gain, 95mW Stereo Headphone Amplifier General Description The LM48820 is a ground referenced, fixed-gain audio power amplifier capable of delivering 95mW of continuous average power into a 16Ω single-ended load, with less than 1% THD +N from a 3V power supply. The LM48820 features a new circuit technology that utilizes a charge pump to generate a negative reference voltage. This allows the outputs to be biased about ground, thereby eliminating output-coupling capacitors typically used with normal single-ended loads. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal number of external components. The LM48820 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other portable applications. The LM48820 features a low-power consumption shutdown mode selectable for each channel and a soft start function that reduces start-up current transients. Additionally, the LM48820 features an internal thermal shutdown protection mechanism. The LM48820 contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM48820 has an internal fixed gain of 1.5V/V. Key Specifications ■ Improved PSRR at 217Hz ■ Power Output at VDD = 3V, RL = 16Ω, THD+N = 1% 95mW (typ) 0.05µA (typ) 1.5V/V (typ) 1.6V to 4.5V 80dB (typ) ■ Shutdown Current ■ Internal Fixed Gain ■ Wide Operating Voltage Range Features ■ Available in space saving 0.4mm pitch micro SMD ■ ■ ■ ■ ■ package Fixed Logic Levels Ground referenced outputs High PSRR Ultra low current shutdown mode Improved pop & click circuitry eliminates noises during turn-on and turn-off transitions ■ No output coupling capacitors, snubber networks, bootstrap capacitors, or gain-setting resistors required ■ Shutdown either channel independently ■ Soft start feature reduces start up transient current Applications ■ ■ ■ ■ ■ Mobile Phones MP3 Players PDAs Portable electronic devices Notebook PCs Boomer® is a registered trademark of National Semiconductor Corporation. © 2007 National Semiconductor Corporation 202023 www.national.com LM48820 Typical Application 202023b8 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM48820 Connection Diagrams micro SMD Package 14 – Bump TM Marking 20202378 Top View XY – Date Code TT – Lot Traceability G – Boomer Family I7 – LM48820TM 20202309 Top View Order Number LM48820TM See NS Package Number TME14AAA TME14 Package View 20202397 3 www.national.com LM48820 Pin Descriptions Pin A1 A2 A3 A4 B1 B2 B4 C1 C2 C4 D1 D2 D3 D4 Name RIN SGND CPVDD CCP+ SD_RC SD_LC PGND LIN ROUT CCPAVDD LOUT -AVDD VCP_OUT Right Channel Input Signal Ground Charge Pump Power Supply Positive Terminal - Charge Pump Flying Capacitor Active-Low Shutdown, Right Channel Active-Low Shutdown, Left Channel Power Ground Left Channel Input Right Channel Output Negative Terminal - Charge Pump Flying Capacitor Positive Power Supply - Amplifier Left Channel Output Negative Power Supply - Amplifier Charge Pump Power Output Function www.national.com 4 LM48820 Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) 4.75V −65°C to +150°C -0.3V to VDD + 0.3V Internally Limited 2000V 200V Junction Temperature Thermal Resistance  θJA (Note 9) 150°C 86°C/W (typ) Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (VDD) −40°C ≤ TA ≤ 85°C 1.6V ≤ VDD ≤ 4.5V Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for VDD = 3V, 16Ω load, and the conditions shown in “Typical Audio Amplifier Application Circuit” (see Figure 1) unless otherwise specified. Limits apply to TA = 25°C. LM48820 Symbol Parameter Conditions VIN = 0V, inputs terminated both channels enabled VIN = 0V, inputs terminated one channel enabled SD_LC = SD_RC = GND RL = 32Ω, VIN = 0V Typical (Note 6) 4.7 3 0.05 1 –1.5 1 20 THD+N = 1% (max); f = 1kHz, one channel THD+N = 1% (max); f = 1kHz, RL = 32Ω, one channel THD+N = 1% (max); f = 1kHz, two channels in phase THD+N = 1% (max); f = 1kHz, RL = 32Ω, two channels in phase PO = 60mW, f = 1kHz, single channel PO = 50mW, f = 1kHz, RL = 32Ω single channel VRIPPLE = 200mVP-P, Input Referred f = 217Hz f = 1kHz f = 20kHz RL = 32Ω, PO = 20mW, (A-weighted) f = 1kHz, BW = 20Hz to 22kHz VDD = 1.8V to 4.2V VDD = 1.8V to 4.2V PO = 1.6mW, f = 1kHz SD_LC = SD_RC = GND Input Terminated Input not terminated 70 30 30   25 95 80 50 55 0.01 0.007 40 45 15 25 2 5 Limit (Notes 7, 8) 5.5 Units (Limits) mA (max) mA (max) µA (max) mV (max) V/V % kΩ (min) kΩ (max) mW mW mW (min) mW (min) % % IDD Quiescent Power Supply Current Full Power Mode Shutdown Current Output Offset Voltage Voltage Gain Gain Match Input Resistance ISD VOS AV Δ AV RIN PO Output Power THD+N Total Harmonic Distortion + Noise PSRR Power Supply Rejection Ratio Full Power Mode 80 75 58 100 1.2 0.45 dB dB dB dB V (min) V (max) dB kΩ (min) SNR VIH VIL XTALK ZOUT Signal-to-Noise Ratio Shutdown Input Voltage High Shutdown Input Voltage Low Crosstalk Output Impedance 5 www.national.com LM48820 LM48820 Symbol Parameter Conditions SD_LC = SD_RC = GND ZOUT IL Output Impedance Input Leakage Note 1: All voltages are measured with respect to the GND pin unless otherwise specified. Typical (Note 6) 8 ±0.1 Limit (Notes 7, 8) 2 Units (Limits) –500mV ≤ VOUT ≤ VDD +500mV (Note 10) kΩ (min) nA Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions that guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given; however, the typical value is a good indication of device performance. Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature, TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA) / θJA or the number given in Absolute Maximum Ratings, whichever is lower. See power dissipation curves for more information Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5: Machine Model, 220pF - 240pF discharged through all pins. Note 6: Typicals are measured at 25°C and represent the parametric norm. Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 9: θJA value is measured with the device mounted on a PCB with a 3” x 1.5”, 1oz copper heatsink. Note 10: VOUT refers to signal applied to the LM48820 outputs. External Components Description (Figure 1) Components 1. 2 3. 4. 5. CINR/INL CC CSS CS1 CS2 Functional Description Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a high-pass filter with Ri at fC = 1/(2πRiCIN). Refer to the section Proper Selection of External Components, for an explanation of how to determine the value of Ci. Flying capacitor. Low ESR ceramic capacitor (≤100mΩ) Output capacitor. Low ESR ceramic capacitor (≤100mΩ) Tantalum capacitor. Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. Ceramic capacitor. Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. www.national.com 6 LM48820 Typical Performance Characteristics THD+N vs Frequency VDD = 1.6V, RL = 16Ω, Stereo, PO = 3mW THD+N vs Frequency VDD = 1.6V, RL = 32Ω, Stereo, PO = 3mW 202023a0 202023a1 THD+N vs Frequency VDD = 3V, RL = 16Ω, Stereo, PO = 25mW THD+N vs Frequency VDD = 3V, RL = 32Ω, Stereo, PO = 25mW 202023a3 202023a5 THD+N vs Frequency VDD = 3V, RL = 16Ω, One channel, PO = 60mW THD+N vs Frequency VDD = 3V, RL = 32Ω, One channel, PO = 50mW 202023a2 202023a4 7 www.national.com LM48820 THD+N vs Output Power VDD = 1.6V, RL = 16Ω, One channel THD+N vs Output Power VDD = 1.6V, RL = 32Ω, One channel 20202321 20202322 THD+N vs Output Power VDD = 1.6V, RL = 16Ω, Stereo THD+N vs Output Power VDD = 1.6V, RL = 32Ω, Stereo 20202323 20202324 THD+N vs Output Power VDD = 3V, RL = 16Ω, One channel THD+N vs Output Power VDD = 3V, RL = 32Ω, One channel 20202398 20202326 www.national.com 8 LM48820 THD+N vs Output Power VDD = 3V, RL = 16Ω, Stereo THD+N vs Output Power VDD = 3V, RL = 32Ω, Stereo 20202327 20202350 Output Power vs Power Supply Voltage RL = 16Ω, f = 1kHz, Mono Output Power vs Power Supply Voltage RL = 16Ω, f = 1kHz, Stereo 20202371 20202372 Output Power vs Power Supply Voltage RL = 32Ω, f = 1kHz, Mono Output Power vs Power Supply Voltage RL = 32Ω, f = 1kHz, Stereo 20202374 20202375 9 www.national.com LM48820 Power Dissipation vs Output Power VDD = 1.6V, RL = 16Ω, f = 1kHz Power Dissipation vs Output Power VDD = 1.6V, RL = 32Ω, f = 1kHz 20202389 20202390 Power Dissipation vs Output Power VDD = 3V, RL = 16Ω, f = 1kHz Power Dissipation vs Output Power VDD = 3V, RL = 32Ω, f = 1kHz 20202391 20202392 PSRR vs Frequency VDD = 1.6V, RL = 16Ω PSRR vs Frequency VDD = 1.6V, RL = 32Ω 20202364 20202366 www.national.com 10 LM48820 PSRR vs Frequency VDD = 3V, RL = 16Ω PSRR vs Frequency VDD = 3V, RL = 32Ω 20202367 20202368 Power Supply Current vs Power Supply Voltage VIN = 0V, Mono Power Supply Current vs Power Supply Voltage VIN = 0V, Stereo 20202376 20202377 11 www.national.com LM48820 Application Information SUPPLY VOLTAGE SEQUENCING Before applying any signal to the inputs or shutdown pins of the LM48820, it is important to apply a supply voltage to the VDD pins. After the device has been powered, signals may be applied to the shutdown pins (see MICRO POWER SHUTDOWN) and input pins. ELIMINATING THE OUTPUT COUPLING CAPACITOR The LM48820 features a low noise inverting charge pump that generates an internal negative supply voltage. This allows the outputs of the LM48820 to be biased about GND instead of a nominal DC voltage, like traditional headphone amplifiers. Because there is no DC component, the large DC blocking capacitors (typically 220µF) are not necessary. The coupling capacitors are replaced by two, small ceramic charge pump capacitors, saving board space and cost. Eliminating the output coupling capacitors also improves low frequency response. In traditional headphone amplifiers, the headphone impedance and the output capacitor form a high pass filter that not only blocks the DC component of the output, but also attenuates low frequencies, impacting the bass response. Because the LM48820 does not require the output coupling capacitors, the low frequency response of the device is not degraded by external components. In addition to eliminating the output coupling capacitors, the ground referenced output nearly doubles the available dynamic range of the LM48820 when compared to a traditional headphone amplifier operating from the same supply voltage. OUTPUT TRANSIENT ('CLICK AND POPS') ELIMINATED The LM48820 contains advanced circuitry that virtually eliminates output transients ('clicks and pops'). This circuitry prevents all traces of transients when the supply voltage is first applied or when the part resumes operation after coming out of shutdown mode. AMPLIFIER CONFIGURATION EXPLANATION As shown in Figure 2, the LM48820 has two internal operational amplifiers. The two amplifiers have internally configured gain, the closed loop gain is set by selecting the ratio of Rf to Ri. Consequently, the gain for each channel of the IC is AV = -(Rf / Ri) = 1.5 (V/V) where RF = 30kΩ and Ri = 20kΩ. POWER DISSIPATION Power dissipation is a major concern when using any power amplifier and must be thoroughly understood to ensure a successful design. Equation 1 states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified output load. PDMAX = (VDD) 2 / (2π2RL) (W) (2) (1) amplifier. Thus the maximum package dissipation point is 56mW. The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation 3: PDMAX = (TJMAX - TA) / (θJA) (W) (3) For this micro SMD package, θJA = 86°C/W and TJMAX = 150° C. Depending on the ambient temperature, TA, of the system surroundings, Equation 3 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 is greater than that of Equation 1, then either the supply voltage must be decreased, the load impedance increased or TA reduced. For the typical application of a 3V power supply, with a 16Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 127°C provided that device operation is around the maximum power dissipation point. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature may be increased accordingly. POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. Applications that employ a 3V power supply typically use a 4.7µF capacitor in parallel with a 0.1µF ceramic filter capacitor to stabilize the power supply output, reduce noise on the supply line, and improve the supply's transient response. Keep the length of leads and traces that connect capacitors between the LM48820's power supply pin and ground as short as possible. MICRO POWER SHUTDOWN The voltage applied to the SD_LC (shutdown left channel) pin and the SD_RC (shutdown right channel) pin controls the LM48820’s shutdown function. When active, the LM48820’s micropower shutdown feature turns off the amplifiers’ bias circuitry, reducing the supply current. The trigger point is 0.45V (max) for a logic-low level, and 1.2V (min) for logic-high level. The low 0.05µA (typ) shutdown current is achieved by applying a voltage that is as near as ground a possible to the SD_LC/SD_RC pins. A voltage that is higher than ground may increase the shutdown current. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100kΩ pull-up resistor between the SD_LC/SD_RC pins and VDD. Connect the switch between the SD_LC/SD_RC pins and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the SD_LC/SD_RC pins to ground, activating micro-power shutdown. The switch and resistor guarantee that the SD_LC/SD_RC pins will not float. This prevents unwanted state changes. In a system with a microprocessor or microcontroller, use a digital output to apply the control voltage to the SD_LC/SD_RC pins. Driving the SD_LC/SD_RC pins with active circuitry eliminates the pull-up resistor. SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM48820's performance requires properly selecting external components. Though the LM48820 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values. 12 Since the LM48820 has two operational amplifiers in one package, the maximum internal power dissipation point is twice that of the number which results from Equation 2. Even with large internal power dissipation, the LM48820 does not require heat sinking over a large range of ambient temperatures. From Equation 2, assuming a 3V power supply and a 16Ω load, the maximum power dissipation point is 28mW per www.national.com LM48820 Charge Pump Capacitor Selection Use low (