LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D Enhancement, and Headphone Sense General Description Key Specifications The LM49270 is a fully integrated audio subsystem designed for stereo multimedia applications. The LM49270 combines a 2.2W stereo Class D amplifier with a 155mW stereo headphone amplifier, volume control, headphone sense, and National’s unique 3D sound enhancement into a single device. The LM49270 uses flexible I2C control interface for multiple application requirements. The filterless stereo class D amplifiers delivers 2.2W/channel into a 4Ω load with less than 10% THD+N with a 5V supply. The headphone amplifier features National’s Output Capacitor-less (OCL) architecture that eliminates the output coupling capacitors required by traditional headphone amplifiers. The IC features a headphone sense input (HPS) that automatically detects the presence of a headphone and configures the device accordingly. The LM49270 can automatically switch from OCL headphone output to a line driver output. If the VOC pin is pulled to GND, the VOC amplifier is disabled and the VOC pin is internally set to GND. This feature allows the LM49270 to be used as a line driver in OCL mode without a GND conflict on the headphone jack sleeve. Additionally, the headphone amplifier can be configured as capacitively coupled (CC). The LM49270 features a 32 step volume control for the headphone and stereo outputs. The device mode select and volume are controlled through an I2C compatible interface. Output short circuit and thermal shutdown protection prevent the device from being damaged during fault conditions. Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. The LM49270 is available in a space saving 28-pin, 5x5mm LLP package. ■ Stereo Class D Amplifier Efficiency: VDD = 3.3V, 450mW/Ch into 8Ω 84% VDD = 5V, 1W/Ch into 8Ω 84% ■ Quiescent Power Supply Current, VDD = 3.3V Speaker Mode Headphone Mode (OCL) 5.5mA 4mA ■ Power Output/Channel, VDD = 5V Class D Speaker amplifier: RL = 4Ω, THD+N = ≤ 10% 2.2W RL = 8Ω, THD+N = ≤ 1% 1.06W Headphone amplifier: RL = 16Ω, THD+N = ≤ 1% 155mW RL = 32Ω, THD+N = ≤ 1% 90mW ■ Shutdown current 0.02μA Features ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Stereo filterless Class D amplifier Selectable OCL/CC headphone amplifier Headphone sense ability National’s 3D Enhancement RF suppression I2C control interface 32-step digital volume control 6 Operating Modes Output short circuit protection and thermal shutdown protection Minimum external components Click and Pop suppression Micro-power shutdown Independent speaker and headphone volume controls Available in space-saving 28 pin LLP package Applications ■ ■ ■ ■ Portable DVD players Smart phones PDAs Laptops Boomer® is a registered trademark of National Semiconductor Corporation. © 2007 National Semiconductor Corporation 202129 www.national.com LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D Enhancement, and Headphone Sense December 2006 LM49270 Typical Application 20212994 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM49270 Connection Diagrams SQ Package 5mm x 5mm x 0.8mm 20212990 Top View Order Number LM49270SQ See NS Package Number NSQAQ028 SQ Markings 20212901 Top View NS = National Logo U = Fab Code Z = Assembly Plant XY = 2 Digit date code TT = Die Traceability 49270SQ = LM49270SQ 3 www.national.com LM49270 TABLE 1. Pin Descriptions PIN NAME DESCRIPTION 1 RHP Right channel headphone output 2 VOC VDD/2 buffer output 3 LHP Left channel headphone output 4 HPVDD Headphone supply input 5 R3DIN Right channel 3D input 6 L3DIN Left channel 3D input 7 BYPASS 8 LIN Left channel input 9 RIN Right channel input 10 GND Analog ground Bias bypass 11 NC 12 LSVDD No connect Speaker supply voltage input 13 RLS+ Right channel non-inverting speaker output 14 RLS- Right channel inverting speaker output 15 NC No connect 16 NC No connect 17 I2CVDD I2C supply voltage input 18 LSGND Speaker ground 19 VDD Power supply 20 ADR Address 21 NC No connect 22 LLS- Left channel inverting speaker output 23 LLS+ Left channel non-inverting speaker output 24 LSVDD Speaker supply voltage input 25 SDA Serial data input 26 SCL Serial clock input 27 HPS Headphone sense input 28 GND Headphone ground www.national.com 4 θJA If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility(Note 4) ESD Susceptibility (Note 5) Junction Temperature (TJMAX) 35.1°C/W Operating Ratings (Notes 1, 2) Temperature Range 6.0V −65°C to +150°C –0.3V to VDD +0.3V Internally Limited 2000V 200V 150°C TMIN ≤ TA ≤ TMAX Supply Voltage (VDD, LSVDD, HPVDD) I2C Voltage (I2CVDD) −40°C ≤ TA ≤ 85°C 2.4V ≤ VDD ≤ 5.5V 2.4V ≤ I2CVDD ≤ 5.5V Electrical Characteristics VDD = 3.3V (Notes 1, 2) The following specifications apply for Headphone: AV = 0dB, RL(HP) = 32Ω; for Loudspeakers: AV = 6dB, RL(SP) = 15μH + 8Ω + 15μH , f = 1kHz, unless otherwise specified. Limits apply for TA = 25°C. LM49270 Symbol Parameter IDD Supply Current ISD Shutdown Supply Current VOS Output Offset Voltage Conditions VIN = 0, RL = No Load, Both channels active Speaker ON, HP OFF Speaker OFF, CC HP ON Speaker OFF, OCL HP ON Headphone Speaker Units (Limits) Typical Limit (Note 6) (Notes 7, 8) 5.5 3 4 7.6 4.7 5.75 mA (max) mA (max) mA (max) 0.02 2 μA (max) 10 10 25 60 mV (max) mV (max) 700 450 400 mW mW (min) Speaker Mode, f = 1kHz THD+N = 1% RL = 4Ω RL = 8Ω THD+N = 10% RL = 4Ω RL = 8Ω 870 560 mW mW CC Headphone Mode, f = 1kHz THD+N = 1% RL = 16Ω POUT Output Power 60 36 RL = 32Ω THD+N = 10% RL = 16Ω RL = 32Ω 30 74 55 mW mW (min) mW mW OCL Headphone Mode, f = 1kHz THD+N = 1% RL = 16Ω 60 36 RL = 32Ω THD+N = 10% RL = 16Ω RL = 32Ω 5 73 55 30 mW mW (min) mW mW www.national.com LM49270 Thermal Resistance Absolute Maximum Ratings (Notes 1, 2) LM49270 LM49270 Symbol THD+N eN η Xtalk Parameter www.national.com (Notes 7, 8) % 0.015 % OCL Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω Noise Efficiency Crosstalk Turn-off Time HPS(Th) (Note 6) Units (Limits) 0.02 TOFF PSRR Limit CC Headphone Mode, f = 1kHz Total Harmonic Distortion + Noise POUT = 12mW, RL = 32Ω Turn-on Time AV Typical Speaker Mode, f = 1kHz POUT = 100mW, RL = 8Ω TON ZIN Conditions Input Impedance Gain Power Supply Rejection Ratio Headphone Sense Threshold 0.02 % Speaker Mode, A-Wtg, Input Referred 47 μV CC Headphone Mode, A-Wtg, Input Referred 10 μV OCL Headphone Mode, A-Wtg, Input Referred 11 μV Speaker Mode RL = 8Ω 84 % Speaker Mode, f = 1kHz, VIN = 1Vp-p 71 dB CC Headphone Mode, f = 1kHz, VIN = 1Vp-p 70 dB OCL Headphone Mode, f = 1kHz, VIN = 1Vp-p 55 dB 30 ms 64 ms Maximum Gain 23.5 kΩ Minimum Gain 210 kΩ Maximum Gain, Speaker Mode 30 dB Minimum Gain, Speaker Mode –47 dB Maximum Gain, Headphone Mode 18 dB Minimum Gain, Headphone Mode –59 dB Speaker Mode, VRIPPLE = 200mVp-p Sine f = 217Hz f = 1kHz 68 68 dB dB Headphone Mode, VRIPPLE = 200mVp-p Sine, CC Mode f = 217Hz f = 1kHz 73 73 dB dB Headphone Mode, VRIPPLE = 200mVp-p Sine, OCL Mode f = 217Hz f = 1kHz 75 79 dB dB Detect Headphone 2.9 V (min) Detect no Headphone 1.8 V (max) 6 LM49270 Symbol Parameter IDD Supply Current ISD Shutdown Supply Current VOS Output Offset Voltage Conditions VIN = 0, RL = No Load, Both channels active Speaker ON, HP OFF Speaker OFF, CC HP ON Speaker OFF, OCL HP ON Headphone Speaker Units (Limits) Typical Limit (Note 6) (Notes 7, 8) 8.5 3.6 4.7 12.4 5.5 6.5 0.15 2 μA (max) 10 10 25 60 mV (max) mV (max) mA (max) mA (max) mA (max) Speaker Mode, f = 1kHz, THD+N = 1% RL = 4Ω 1.75 1.06 W W 2.2 1.35 W W 155 90 mW mW 177 140 mW mW 155 90 mW mW RL = 32Ω 175 140 mW mW Speaker Mode, f = 1kHz POUT = 100mW, RL = 8Ω 0.03 % CC Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω 0.02 % OCL Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω RL = 8Ω THD+N = 10 % RL = 4Ω RL = 8Ω CC Headphone Mode, f = 1kHz, THD+N = 1% RL = 16Ω POUT Output Power RL = 32Ω THD+N = 10% RL = 16Ω RL = 32Ω OCL Headphone Mode, f = 1kHz, THD+N = 1% RL = 16Ω RL = 32Ω THD+N = 10% RL = 16Ω THD+N eN η Total Harmonic Distortion + Noise Noise Efficiency 0.03 % Speaker Mode, A-Wtg, Input Referred 47 μV CC Headphone Mode, A-Wtg, Input Referred 10 μV OCL Headphone Mode, A-Wtg, Input Referred 11 μV Speaker Mode RL = 8Ω 84 % 7 www.national.com LM49270 Electrical Characteristics VDD = 5.0V (Notes 2, 1) The following specifications apply for Headphone” AV = 0dB, RL(HP) = 32Ω,: for Loudspeakers: AV = 6dB, RL(SP) = 15μH + 8Ω + 15μH, f = 1kHz unless otherwise specified. Limits apply for TA = 25°C. LM49270 LM49270 Symbol Xtalk Parameter Crosstalk TON Turn-on Time TOFF Turn-off Time ZIN AV PSRR HPS(Th) Input Impedance Gain Power Supply Rejection Ratio Headphone Sense Threshold Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) Speaker Mode, f = 1kHz, VIN = 1Vp-p –85 dB CC Headphone Mode, f = 1kHz, VIN = 1Vp-p –70 dB OCL Headphone Mode, f = 1kHz, VIN = 1Vp-p –58 dB 43 ms 100 ms Maximum Gain 23.5 kΩ Minimum Gain 210 kΩ Maximum Gain, Speaker Mode 30 dB Minimum Gain, Speaker Mode –47 dB Maximum Gain, Headphone Mode 18 dB Minimum Gain, Headphone Mode –59 dB Speaker Mode, VRIPPLE = 200mVp-p Sine f = 217Hz f = 1kHz 61 61 dB dB Headphone Mode, VRIPPLE = 200mVp-p Sine, CC Mode f = 217Hz f = 1kHz 75 74 dB min Headphone Mode, VRIPPLE = 200mVp-p Sine, OCL Mode f = 217Hz f = 1kHz 78 75 dB dB Detect Headphone Detect no Headphone 4.4 V (min) 3 V (max) Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. 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 which 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. For the LM49270 see power derating currents 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. www.national.com 8 LM49270 Typical Performance Characteristics THD+N vs Output Power Speaker Mode AV = 6dB, RL = 4Ω, f = 1kHz THD+N vs Output Power Speaker Mode AV = 6dB, RL = 8Ω, f = 1kHz 20212902 20212903 THD+N vs Output Power OCL Headphone Mode AV = 0dB, RL = 16Ω, f = 1kHz THD+N vs Output Power OCL Headphone Mode AV = 0dB, RL = 32Ω, f = 1kHz 20212909 20212908 THD+N vs Output Power CC Headphone Mode AV = 0dB, RL = 32Ω, f = 1kHz THD+N vs Output Power CC Headphone Mode AV = 0dB, RL = 16Ω, f = 1kHz 20212915 20212914 9 www.national.com LM49270 THD+N vs Frequency Speaker Mode VDD = 3.3V, POUT = 300mW, RL = 4Ω THD+N vs Frequency Speaker Mode VDD = 5V, POUT = 500mW, RL = 4Ω 20212904 20212905 THD+N vs Frequency Speaker Mode VDD = 3.3V, POUT = 200mW, RL = 8Ω THD+N vs Frequency Speaker Mode VDD = 5V, POUT = 350mW, RL = 8Ω 20212907 20212906 THD+N vs Frequency OCL Headphone Mode VDD = 3.3V, POUT = 45mW, RL = 16Ω THD+N vs Frequency OCL Headphone Mode VDD = 5V, POUT = 100mW, RL = 16Ω 20212910 www.national.com 20212911 10 LM49270 THD+N vs Frequency OCL Headphone Mode VDD = 3.3V, POUT = 25mW, RL = 32Ω THD+N vs Frequency OCL Headphone Mode VDD = 5V, POUT = 70mW, RL = 32Ω 20212913 20212912 THD+N vs Frequency CC Headphone Mode VDD = 3.3V, POUT = 45mW, RL = 16Ω THD+N vs Frequency CC Headphone Mode VDD = 5V, POUT = 100mW, RL = 16Ω 20212916 20212917 THD+N vs Frequency CC Headphone Mode VDD = 3.3V, POUT = 25mW, RL = 32Ω THD+N vs Frequency CC Headphone Mode VDD = 5V, POUT = 70mW, RL = 32Ω 20212918 20212919 11 www.national.com LM49270 PSRR vs Frequency Speaker Mode VDD = 3.3V, VRIPPLE = 200mVP-P, RL = 8Ω PSRR vs Frequency OCL Headphone Mode VDD = 3.3V, VRIPPLE = 200mVP-P, RL = 32Ω 202129a3 202129a2 PSRR vs Frequency CC Headphone Mode VDD = 3.3V, VRIPPLE = 200mVP-P, RL = 32Ω Efficiency vs Output Power Speaker Mode RL = 4Ω, f = 1kHz 202129a4 20212967 Efficiency vs Output Power Speaker Mode RL = 8Ω, f = 1kHz Power Dissipation vs Output Power Speaker Mode RL = 4Ω, f = 1kHz 20212968 www.national.com 20212969 12 LM49270 Power Dissipation vs Output Power Speaker Mode RL = 8Ω, f = 1kHz Power Dissipation vs Output Power OCL Headphone Mode RL = 16Ω, f = 1kHz 20212998 20212970 Power Dissipation vs Output Power OCL Headphone Mode RL = 32Ω, f = 1kHz Power Dissipation vs Output Power CC Headphone Mode RL = 16Ω, f = 1kHz 20212982 20212977 Power Dissipation vs Output Power CC Headphone Mode RL = 32Ω, f = 1kHz Output Power vs Supply Voltage Speaker Mode RL = 4Ω, f = 1kHz 20212971 20212983 13 www.national.com LM49270 Output Power vs Supply Voltage Speaker Mode RL = 8Ω, f = 1kHz Output Power vs Supply Voltage OCL Headphone Mode RL = 16Ω, f = 1kHz 20212972 20212995 Output Power vs Supply Voltage OCL Headphone Mode RL = 32Ω, f = 1kHz Output Power vs Supply Voltage CC Headphone Mode RL = 16Ω, f = 1kHz 20212997 20212996 Output Power vs Supply Voltage CC Headphone Mode RL = 32Ω, f = 1kHz Crosstalk vs Frequency Speaker Mode VDD = 3.3V, VRIPPLE = 1VP-P, RL = 8Ω 202129a0 20212985 www.national.com 14 LM49270 Crosstalk vs Frequency OCL Headphone Mode VDD = 3.3V, VRIPPLE = 1VP-P, RL = 32Ω Crosstalk vs Frequency CC Headphone Mode VDD = 3.3V, VRIPPLE = 1VP-P, RL = 32Ω 20212989 202129a1 Supply Current vs Supply Voltage Speaker Mode, No Load Supply Current vs Supply Voltage OCL Headphone Mode, No Load 20212975 20212981 Supply Current vs Supply Voltage CC Headphone Mode, No Load Turn-On Speaker Mode 20212988 20212927 15 www.national.com LM49270 Turn-Off Speaker Mode Turn-On OCL Headphone Mode 20212929 20212928 Turn-Off OCL Headphone Mode Turn-On CC Headphone Mode 20212931 20212930 Turn-Off CC Headphone Mode 20212932 www.national.com 16 word. Each transmission sequence is framed by a START condition and a STOP condition. Each word (register address + register content) transmitted over the bus is 8 bits long and is always followed by an acknowledge pulse. To avoid an address conflict with another device on the I2C bus, the LM49270 address is determined by the ADR pin, the state of ADR determines address bit A1 (Table 2). When ADR = 0, the address is 1111 1000. When ADR = 1 the device address is 1111 1010. I2C COMPATIBLE INTERFACE The LM49270 is controlled through an I2C compatible serial interface that consists of a serial data line (SDA) and a serial clock (SCL). The clock line is uni-directional. The data line is bi-directional (open-collector), although the LM49270 does not write to the I2C bus. The LM49270 and the master can communicate at clock rates up to 400kHz. Figure 3 shows the I2C interface timing diagram. The LM49270 is a transmit/receive slave-only device, reliant upon the master to generate a clock signal. The master device communicates to the LM49270 by transmitting the proper device address followed by a command TABLE 2. Device Address ADR A7 A6 A5 A4 A3 A2 A1 A0 X 1 1 1 1 1 0 X 0 0 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 1 0 TABLE 3. I2C Control Registers REG Register Name D7 D6 D5 D4 D3 D2 D1 D0 0 Shutdown Control 0 0 — — HP3DSEL LS3DSEL OCL/CC PWR_ON 1 Headphone Gain Control 0 1 — HP4 HP3 HP2 HP1 HP0 2 Speaker Gain Control 1 0 — LS4 LS3 LS2 LS1 LS0 Note: OCL/CC = 1 selects OCL mode; OCL/CC = 0 selects cap coupled mode PWR_ON = 0 puts part in shutdown After the last address bit is sent, the master device releases the data line, during which time, an acknowledge clock pulse is generated. If the LM49270 receives the address correctly, then the LM49270 pulls the data line low, generating an acknowledge bit (ACK). Once the master device has registered the ACK bit, the 8-bit register address/data word is sent. Each data bit should be stable while the clock level is high. After the 8–bit word is sent, the LM49270 sends another ACK bit. Following the acknowledgement of the data word, the master device issues a “stop” bit, allowing SDA to go high while the clock signal is high. BUS FORMAT The I2C bus format is shown in Figure 2. The “start” signal is generated by lowering the data signal while the clock is high. The start signal alerts all devices on the bus that a device address is being written to the bus. The 8-bit device address is written to the bus next, most significant bit first. The data is latched in on the rising edge of the clock. Each address bit must be stable while the clock is high. 20212991 FIGURE 2. I2C Bus Format 17 www.national.com LM49270 Application Information LM49270 20212992 FIGURE 3. I2C Timing Diagram GENERAL AMPLIFIER FUNCTION Capacitor Coupled Headphone Mode In capacitor coupled (CC) mode, the VOC pin is disabled, and the headphone outputs are coupled to the jack through series capacitors, allowing the headphone return to be connected to GND (Figure 4). In CC mode, the LM49270 requires output coupling capacitors to block the DC component of the amplifier output, preventing DC current from flowing to the load. The output capacitor and speaker impedance form a high pass filter with a -3dB roll-off determined by: Class D Amplifier The LM49270 features a high-efficiency, filterless, Class D stereo amplifier. The LM49270 Class D amplifiers feature a filterless modulation scheme known as Class BD. The differential outputs of each channel switch at 300kHz from VDD to GND. When there is no input signal applied, the two outputs (LLS+ and LLS-) switch in phase with a 50% duty cycle. Because the outputs of the LM49270 are differential, there is in no net voltage across the speaker, thus no load current during the idle state conserving power. When an input signal is applied, the duty cycle (pulse width) of each output changes. For increasing output voltages, the duty cycle of LLS+ increases, while the duty cycle of LLSdecreases. For decreasing output voltages, the converse occurs. The duty cycle of LLS- increases while the duty cycle of LLS+ decreases. The difference between the two pulse widths yields the differential output voltage. f-3dB = 1 / 2πRLCOUT Where RL is the headphone impedance, and COUT is the output coupling capacitor. Choose COUT such that f-3dB is well below the lowest frequency of interest. Setting f-3dB too high results in poor low frequency performance. Select capacitor dielectric types with low ESR to minimize signal loss due to capacitor series resistance and maximize power transfer to the load. Headphone Amplifier The LM49270 headphone amplifier features two different operating modes, output capacitor-less (OCL) and capacitor coupled (CC). The OCL architecture eliminates the bulky, expensive output coupling capacitors required by traditional headphone amplifiers. The LM49270 headphone section uses three amplifiers. Two amplifiers drive the headphones while the third (VOC) is set to the internally generated bias voltage (typically VDD/2). The third amplifier is connected to the return terminal (sleeve) of the headphone jack. In this configuration, the signal side of the headphones are biased to VDD/2, the return is biased to VDD/2, thus there is no net DC voltage across the headphone eliminating the need for an output coupling capacitor. Removing the output coupling capacitors from the headphone signal path reduces component count, reducing system cost and board space consumption, as well as improving low frequency performance and sound quality. The voltage on the return sleeve is not an issue when driving headphones. However, if the headphone output is used as a line out, the VDD/2 can conflict with the GND potential that a line-in would expect on the return sleeve. When the return of the headphone jack is connected to GND, the LM49270 detects an output short circuit condition and the VOC amplifier is disabled preventing damage to the LM49270 and allowing the headphone return to be biased at GND. www.national.com 20212993 FIGURE 4. Capacitor Coupled Headphone Mode Headphone Sense The LM49270 features a headphone sense input (HPS) that monitors the headphone jack and configures the device depending on the presence of a headphone. When the HPS pin is low, indicating that a headphone is not present, the LM49270 speaker amplifiers are active and the headphone 18 In OCL mode, the maximum power dissipation increases due to the use of a third amplifier as a buffer. The power dissipation is given by: PDMAX(OCL) = VDD2/π2RL POWER DISSIPATION AND EFFICIENCY The major benefit of Class D amplifier is increased efficiency versus Class AB. The efficiency of the LM49270 speaker amplifiers is attributed to the output transistors’ region of operation. The Class D output stage acts as current steering switches, consuming negligible amounts of power compared to their Class AB counterparts. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET on-resistance (RDS(ON)) , along with the switching losses due to gate charge. The maximum power dissipation per headphone channel in Capacitor Coupled mode is given by: SHUTDOWN FUNCTION The LM49270 features a shutdown mode configured through the I2C interface. Bit D0 (PWR_ON) in the Shutdown Control register shuts down/turns on the entire device. Set PWR_ON = 1 to enable the LM49270, set PWR_ON = 0 to disable the device. AUDIO AMPLIFIER GAIN SETTING Each channel of the LM49270 features a 32 step volume control. The loudspeaker volume has a range of -47dB to 30dB and the headphone has a range of -59dB to 18dB (see Table 4). PDMAX(CC) = VDD2/2π2RL TABLE 4. Volume Control Volume Step LS4/HP4 LS3/HP3 LS2/HP2 LS1/HP1 LS0/HP0 LS Gain (dB) HP Gain (dB) 1 0 0 0 0 0 –47 –59 2 0 0 0 0 1 –36 –48 3 0 0 0 1 0 –28.5 –46.5 4 0 0 0 1 1 –22.5 –34.5 5 0 0 1 0 0 –18 –30 6 0 0 1 0 1 –15 –27 7 0 0 1 1 0 –12 –24 8 0 0 1 1 1 –9 –21 9 0 1 0 0 0 –6 –18 10 0 1 0 0 1 –3 –15 11 0 1 0 1 0 –1.5 –13.5 12 0 1 0 1 1 0 –12 13 0 1 1 0 0 1.5 –10.5 14 0 1 1 0 1 3 –9 15 0 1 1 1 0 4.5 –7.5 16 0 1 1 1 1 6 –6 17 1 0 0 0 0 7.5 –4.5 18 1 0 0 0 1 9 –3 19 1 0 0 1 0 10.5 –1.5 20 1 0 0 1 1 12 0 21 1 0 1 0 0 13.5 1.5 22 1 0 1 0 1 15 3 23 1 0 1 1 0 16.5 4.5 24 1 0 1 1 1 18 6 25 1 1 0 0 0 19.5 7.5 26 1 1 0 0 1 21 9 27 1 1 0 1 0 22.5 10.5 28 1 1 0 1 1 24 12 29 1 1 1 0 0 25.5 13.5 30 1 1 1 0 1 27 15 31 1 1 1 1 0 28.5 16.5 32 1 1 1 1 1 30 18 19 www.national.com LM49270 amplifiers are disabled. When the HPS pin is high, indicating that a headphone is present, the headphone amplifiers are active while the speaker amplifiers are disabled. LM49270 as close to the device as possible. Typical applications employ a voltage regulator with 10µF and 0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing of the LM49270 supply pins. A 1µF capacitor is recommended. NATIONAL 3D ENHANCEMENT The LM49720 features National’s 3D sound enhancement. 3D sound improves the apparent stereo channel separation whenever the left and right speakers are located close to each other, widening the perceived sound stage in devices with a small form factor that prohibits proper speaker placement. An external RC network , shown in Figure 1, enables the 3D effect. R3D sets the level of the 3D effect; decreasing the value of R3D will increase the 3D effect. The 3D network acts like a high pass filter C3D sets the frequency response; increasing the value of C3D will decrease the low cutoff frequency at which the 3D effect starts to occur, as shown by this equation: f3D(-3dB) = 1/2π(R3D)(C3D) Bypass Capacitor Selection The LM49270 generates a VDD/2 common-mode bias voltage internally. The BYPASS capacitor, CB, improves PSRR and THD+N by reducing noise at the BYPASS node. Use a 1μF capacitor, placed as close to the device as possible for CB. Audio Amplifier Input Capacitor Selection Input capacitors, CIN, in conjunction with the input impedance of the LM49270 forms a high pass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the signal to an optimal DC level. Assuming zero source impedance, the -3dB point of the high pass filter is given by: (1) Enabling the 3D effect increases the gain by a multiplication factor of (1 + 20kΩ/R3D). Setting R3D to 20kΩ results in a 6dB increase (doubling) of the gain, increasing the 3D effect. The level of 3D effect is also dependent on other factors such as speaker placement and the distance from the speakers to the listener. The values of R3D and C3D should be chosen for each application individually, taking into account the physical factors noted before. f(–3dB) = 1/2πRINCIN POWER SUPPLIES The LM49270 uses different supplies for each portion of the device, allowing for the optimum combination of headroom, power dissipation and noise immunity. The speaker amplifier gain stage is powered from VDD, while the output stage is powered from LSVDD. The headphone amplifiers, input amplifiers and volume control stages are powered from HPVDD. The separate power supplies allow the speakers to operate from a higher voltage for maximum headroom, while the headphones operate from a lower voltage, improving power dissipation. HPVDD may be driven by a linear regulator to further improve performance in noisy environments. The I2C portion if powered from I2CVDD, allowing the I2C portion of the LM49270 to interface with lower voltage digital controllers. PROPER SELECTION OF EXTERNAL COMPONENTS Audio Amplifier Power Supply Bypassing/Filtering Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass capacitor www.national.com (2) Choose CIN such that f-3dB is well below that lowest frequency of interest. Setting f-3dB too high affects the low-frequency responses of the amplifier. Use capacitors with low voltage coefficient dielectrics, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies. Other factors to consider when designing the input filter include the constraints of the overall system. Although high fidelity audio requires a flat frequency response between 20Hz and 20kHz, portable devices such as cell phones may only concentrate on the frequency range of the frequency range of the spoken human voice (typically 300Hz to 4kHz). In addition, the physical size of the speakers used in such portable devices limits the low frequency response; in this case, frequencies below 150Hz may be filtered out. 20 LM49270 Revision Table Rev Date Description 1.0 12/19/06 Initial release. 21 www.national.com LM49270 Physical Dimensions inches (millimeters) unless otherwise noted 28 Lead LLP Order Number LM49270SQ NS Package Number NSQAQ028 www.national.com 22 LM49270 Notes 23 www.national.com LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D Enhancement, and Headphone Sense Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. 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