LM48860TL

LM48860 Ground-Referenced, Ultra Low Noise, Fixed Gain Stereo Headphone Amplifier October 17, 2008 LM48860 Ground-Referenced, Ultra Low Noise, Fixed Gain Stereo Headphone Amplifier General Description The LM48860 is a ground referenced, fixed-gain audio power amplifier capable of delivering 40mW per channel of continuous average power into a 16Ω single-ended load with less than 1% THD+N from a 3V power supply. The LM48860 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 amount of external components. The LM48860 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The LM48860 features a low-power consumption shutdown mode selectable for either channel separately. This is accomplished by driving either the SD_RC (Shutdown Right Channel) or SD_LC (Shutdown Left Channel) (or both) pins with logic low, depending on which channel is desired shutdown. Additionally, the LM48860 features an internal thermal shutdown protection mechanism. The LM48860 contains advanced pop & click circuitry that eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM48860 has an internal fixed gain of 1.5V/V. Key Specifications ■ PSRR at 217Hz (VDD = 3.0V) ■ Stereo Power Output at VDD = 3V RL = 16Ω, THD+N = 1% 40mW (typ) 0.1μA (typ) 1.5V/V (typ) 2.0V to 5.5V 80dB (typ) ■ Shutdown Current ■ Internal Fixed Gain ■ Operating Voltage Features ■ ■ ■ ■ ■ ■ Fixed logic levels with supply voltage Ground referenced outputs High PSRR Available in space-saving micro SMD package 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 Applications ■ ■ ■ ■ ■ Mobile Phones MP3 Players PDAs Portable electronic devices Notebook PCs Boomer® is a registered trademark of National Semiconductor Corporation. © 2008 National Semiconductor Corporation 300068 www.national.com LM48860 Typical Application 30006889 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM48860 Connection Diagram LM48860TL Pinout (BUMP DOWN VIEW ) 30006813 Top View Order Number LM48860TL See NS Package Number TLA12XXX Pin Descriptions Pin A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D3 Name RIN SGND LIN ROUT SD_LC LOUT VSS(CP) SD_RC VDD CCPPGND CCP+ Right Channel Input Signal Ground Left Channel Input Right Channel Output Active Low Shutdown, Left Channel Left Channel Output Charge Pump Voltage Output Active-Low Shutdown, Right Channel Supply Voltage Negative Terminal - Charge Pump Flying Capacitor Power Ground Positive Terminal - Charge Pump Flying Capacitor Function 3 www.national.com LM48860 Absolute Maximum Ratings (Notes 2, 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 Rating(Note 4) ESD Rating (Note 5) 6.0V −65°C to +150°C -0.3V to VDD Internally Limited 2000V 200V Junction Temperature Thermal Resistance  θJA (typ) TLA12XXX 150°C 59.3°C/W Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (VDD) −40°C ≤ TA ≤ 85°C 2.0V ≤ VDD ≤ 5.5V Electrical Characteristics VDD = 3V Symbol Parameter (Notes 1, 2) LM48860 Conditions Typical (Note 6) 4 Limit (Note 7) 5.5 The following specifications apply for VDD = 3V and 16Ω load unless otherwise specified. Limits apply to TA = 25°C. Units (Limits) IDD VDD = 3.0V, VIN = 0V, inputs terminated Quiescent Power Supply Current both channels enabled Full Power Mode VDD = 5.0V, VIN = 0V, inputs terminated both channels enabled SD_LC = SD_RC= GND Shutdown Current Output Offset Voltage Voltage Gain Channel-to-channel Gain Matching Input Resistance THD+N = 1% (max); f = 1kHz, RL = 16Ω, (two channels in phase) THD+N = 1% (max); f = 1kHz, RL = 32Ω, (two channels in phase) PO = 20mW, f = 1kHz, RL = 16Ω (two channels in phase) PO = 25mW, f = 1kHz, RL = 32Ω (two channels in phase) VRIPPLE = 200mVPP, Input Referred f = 217Hz f = 1kHz f = 20kHz RL = 32Ω, POUT = 50mW, f = 1kHz, BW = 20Hz to 22kHz, A-weighted VDD = 2.0V to 5.5V VDD = 2.0V to 5.5V RL = 16Ω, PO = 1.6mW, f = 1kHz A-weighted filter, VIN = 0V SD_LC = SD_RC= GND, VDD = 5.0V RL = 32Ω, VIN = 0V mA (max) 4.2 0.1 0.1 0.7 –1.5 1 15 25 35 40 1 1 5.5 mA µA (max) µA (max) mV (max) V/V % kΩ (min) kΩ (max) mW (min) mW (min) % % ISD VOS AV Δ AV RIN 20 40 50 0.025 0.014 PO Output Power THD+N Total Harmonic Distortion + Noise PSRR Power Supply Rejection Ratio Full Power Mode 80 75 60 105 73 dB (min) dB dB dB SNR VIH VIL XTALK ∈OS Signal-to-Noise Ratio Shutdown Input Voltage High Shutdown Input Voltage Low Crosstalk Output Noise 1.2 0.45 75 8 V (min) V (max) dB μV www.national.com 4 LM48860 LM48860 Symbol Parameter Conditions VSD = GND Input Terminated Input not terminated SD_LC = SD_RC = GND Typical (Note 6) Limit (Note 7)   20 Units (Limits) ZOUT Output Impedance 30 30 ±0.1 kΩ (min) kΩ nA IL Input Leakage Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. 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. For the LM48860, see power derating curves for additional information. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: θJA value is measured with the device mounted on a PCB with a 1.5” x 1.375”, 1oz copper heatsink. External Components Description (Figure 1) Components 1. C1 Functional Description Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a high passpass filter with Ri at fC = 1/(2RiC1). Refer to the section Proper Selection of External Components, for an explanation of how to determine the value of C1. Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a high passpass filter with Ri at fC = 1/(2RiC2). Refer to the Power Supply Bypassing section for an explanation of how to determine the value of C2. Output capacitor. Low ESR ceramic capacitor (≤100mΩ) Flying 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. 2. 3. 4. 5. 6. C2 C3 C4 C5 C6 5 www.national.com LM48860 Typical Performance Characteristics THD+N vs Output Power VDD = 3V, RL = 16Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 3V, RL = 16Ω, f = 1kHz 22kHz BW, two channels in phase 300068d2 30006824 THD+N vs Output Power VDD = 3V, RL = 32Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 3V, RL = 32Ω, f = 1kHz 22kHz BW, two channels in phase 300068d3 30006825 THD+N vs Output Power VDD = 3.6V, RL = 16Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 3.6V, RL = 16Ω, f = 1kHz 22kHz BW, two channels in phase 300068c8 300068c9 www.national.com 6 LM48860 THD+N vs Output Power VDD = 3.6V, RL = 32Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 3.6V, RL = 32Ω, f = 1kHz 22kHz BW, two channels in phase 300068d0 300068d1 THD+N vs Output Power VDD = 4.2V, RL = 16Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 4.2V, RL = 16Ω, f = 1kHz 22kHz BW, two channels in phase 300068d4 300068d5 THD+N vs Output Power VDD = 4.2V, RL = 32Ω f = 1kHz, 22kHz BW, one channel enabled THD+N vs Output Power VDD = 4.2V, RL = 32Ω, f = 1kHz 22kHz BW, two channels in phase 300068d6 300068d7 7 www.national.com LM48860 THD+N vs Frequency VDD = 3V, RL = 16Ω PO = 20mW, 22kHz BW THD+N vs Frequency VDD = 3V, RL = 32Ω PO = 20mW, 22kHz BW 30006822 30006823 THD+N vs Frequency VDD = 3.6V, RL = 16Ω PO = 30mW, 22kHz BW THD+N vs Frequency VDD = 3.6V, RL = 32Ω PO = 30mW, 22kHz BW 300068c4 300068c5 THD+N vs Frequency VDD = 4.2V, RL = 16Ω PO = 30mW, 22kHz BW THD+N vs Frequency VDD = 4.2V, RL = 32Ω PO = 30mW, 22kHz BW 300068c7 300068c6 www.national.com 8 LM48860 PSRR vs Frequency VDD = 3V, RL = 16Ω VRIPPLE = 200mVPP PSRR vs Frequency VDD = 3V, RL = 32Ω VRIPPLE = 200mVPP 30006887 30006888 PSRR vs Frequency VDD = 3.6V, RL = 16Ω VRIPPLE = 200mVPP PSRR vs Frequency VDD = 3.6V, RL = 32Ω VRIPPLE = 200mVPP 300068c0 300068c1 PSRR vs Frequency VDD = 4.2V, RL = 16Ω VRIPPLE = 200mVPP PSRR vs Frequency VDD = 4.2V, RL = 32Ω VRIPPLE = 200mVPP 300068c2 300068c3 9 www.national.com LM48860 Output Power vs Supply Voltage RL = 16Ω, f = 1kHz, 22kHz BW Output Power vs Supply Voltage RL = 32Ω, f = 1kHz, 22kHz BW 30006885 30006886 Power Dissipation vs Output Power VDD = 3V, RL = 16Ω, f = 1kHz Power Dissipation vs Output Power VDD = 3V, RL = 32Ω, f = 1kHz 30006894 30006895 Power Dissipation vs Output Power VDD = 5V, RL = 16Ω, f = 1kHz Power Dissipation vs Output Power VDD = 5V, RL = 32Ω, f = 1kHz 30006896 30006897 www.national.com 10 LM48860 Supply Current vs Supply Voltage VIN = GND, No Load Power Derating Curve VDD = 3V, RL = 16Ω 30006898 30006890 Power Derating Curve VDD = 3V, RL = 32Ω Power Derating Curve VDD = 5V, RL = 16Ω 30006891 30006892 Power Derating Curve VDD = 5V, RL = 32Ω 30006893 11 www.national.com LM48860 Application Information SUPPLY VOLTAGE SEQUENCING It is a good general practice to first apply the supply voltage to a CMOS device before any other signal or supply on other pins. This is also true for the LM48860 audio amplifier which is a CMOS device. Before applying any signal to the inputs or shutdown pins of the LM48860, 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 LM48860 features a low noise inverting charge pump that generates an internal negative supply voltage. This allows the outputs of the LM48860 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 LM48860 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 LM48860 when compared to a traditional headphone amplifier operating from the same supply voltage. OUTPUT TRANSIENT ('CLICK AND POPS') ELIMINATED The LM48860 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 LM48860 has two internal operational amplifiers. The two amplifiers have internally configured gain. Since this is an output ground-referenced amplifier, the LM48860 does not require output coupling capacitors. POWER DISSIPATION From the graph (THD+N vs Output Power , VDD = 3V, RL = 16Ω, f = 1kHz, 22kH BW, two channels in phase, page 6) assuming a 3V power supply and a 16Ω load, the maximum power dissipation point and thus the maximum package dissipation point is 281mW. The maximum power dissipation point obtained must not be greater than the power dissipation that results from Equation 1. PDMAX = (TJMAX - TA) / (θJA) (1) graph is greater than that of Equation 1, then either the supply voltage must be decreased, the load impedance increased or TA reduced (see power derating curves). For the application of a 5V power supply, with a 16Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 110°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's 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 LM48860'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 LM48860’s shutdown function. When active, the LM48860’s micropower shutdown feature turns off the amplifiers’ bias circuitry, reducing the supply current. The trigger point is 0.45V for a logic-low level, and 1.2V for logic-high level. The low 0.01µA (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. Do not let SD_LC/SD_RC float, connect either to high or low. SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM48860's performance requires properly selecting external components. Though the LM48860 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values. Charge Pump Capacitor Selection Use low ESR (equivalent series resistance) (