LM49270SQ

LM49270 Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D Enhancement, and Headphone Sense December 2006 LM49270  Filterless 2.2W Stereo Class D Audio Subsystem with OCL Headphone Amplifier, 3D Enhancement, and Headphone Sense General Description 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. Key Specifications ■ Stereo Class D Amplifier Efficiency:  VDD = 3.3V, 450mW/Ch into 8Ω  VDD = 5V, 1W/Ch into 8Ω ■ Quiescent Power Supply Current, VDD = 3.3V  Speaker Mode  Headphone Mode (OCL) ■ Power Output/Channel, VDD = 5V  Class D Speaker amplifier: RL = 4Ω, THD+N = ≤ 10% RL = 8Ω, THD+N = ≤ 1% 2.2W 1.06W 5.5mA 4mA 84% 84%  Headphone amplifier: RL = 16Ω, THD+N = ≤ 1% RL = 32Ω, THD+N = ≤ 1% 155mW 90mW 0.02μA ■ Shutdown current 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 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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 NAME RHP VOC LHP HPVDD R3DIN L3DIN BYPASS LIN RIN GND NC LSVDD RLS+ RLSNC NC I2CVDD LSGND VDD ADR NC LLSLLS+ LSVDD SDA SCL HPS GND Right channel headphone output VDD/2 buffer output Left channel headphone output Headphone supply input Right channel 3D input Left channel 3D input Bias bypass Left channel input Right channel input Analog ground No connect Speaker supply voltage input Right channel non-inverting speaker output Right channel inverting speaker output No connect No connect I2C supply voltage input Speaker ground Power supply Address No connect Left channel inverting speaker output Left channel non-inverting speaker output Speaker supply voltage input Serial data input Serial clock input Headphone sense input Headphone ground DESCRIPTION www.national.com 4 LM49270 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 (Note 1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility(Note 4) ESD Susceptibility (Note 5) Junction Temperature (TJMAX) 6.0V −65°C to +150°C –0.3V to VDD +0.3V Internally Limited 2000V 200V 150°C Thermal Resistance  θJA 35.1°C/W (Notes 1, 2) −40°C ≤ TA ≤ 85°C 2.4V ≤ VDD ≤ 5.5V 2.4V ≤ I2CVDD ≤ 5.5V Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage (VDD, LSVDD, HPVDD) I2C Voltage (I2CVDD) 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 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 Speaker Mode, f = 1kHz THD+N = 1% RL = 4Ω 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 RL = 32Ω 60 36 73 55 mW mW (min) mW mW 60 36 74 55 mW mW (min) mW mW 700 450 870 560 mW mW (min) mW mW Typical (Note 6) Limit (Notes 7, 8) Units (Limits) IDD Supply Current 5.5 3 4 0.02 10 10 7.6 4.7 5.75 2 25 60 mA (max) mA (max) mA (max) μA (max) mV (max) mV (max) ISD VOS Shutdown Supply Current Output Offset Voltage 400 30 30 5 www.national.com LM49270 LM49270 Symbol Parameter Conditions Speaker Mode, f = 1kHz POUT = 100mW, RL = 8Ω CC Headphone Mode, f = 1kHz Total Harmonic Distortion + Noise POUT = 12mW, RL = 32Ω OCL Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω Speaker Mode, A-Wtg, Input Referred eN Noise CC Headphone Mode, A-Wtg, Input Referred OCL Headphone Mode, A-Wtg, Input Referred η Efficiency Speaker Mode RL = 8Ω Speaker Mode, f = 1kHz, VIN = 1Vp-p Xtalk Crosstalk CC Headphone Mode, f = 1kHz, VIN = 1Vp-p OCL Headphone Mode, f = 1kHz, VIN = 1Vp-p TON TOFF ZIN Turn-on Time Turn-off Time Input Impedance Maximum Gain Minimum Gain Maximum Gain, Speaker Mode AV Gain Minimum Gain, Speaker Mode Maximum Gain, Headphone Mode Minimum Gain, Headphone Mode Speaker Mode, VRIPPLE = 200mVp-p Sine f = 217Hz f = 1kHz Headphone Mode, VRIPPLE = 200mVp-p Sine, CC Mode f = 217Hz f = 1kHz Headphone Mode, VRIPPLE = 200mVp-p Sine, OCL Mode f = 217Hz f = 1kHz HPS(Th) Headphone Sense Threshold Detect Headphone Detect no Headphone Typical (Note 6) 0.02 Limit (Notes 7, 8) Units (Limits) % THD+N 0.015 % 0.02 47 10 11 84 71 70 55 30 64 23.5 210 30 –47 18 –59 % μV μV μV % dB dB dB ms ms kΩ kΩ dB dB dB dB 68 68 dB dB PSRR Power Supply Rejection Ratio 73 73 dB dB 75 79 2.9 1.8 dB dB V (min) V (max) www.national.com 6 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 Symbol Parameter 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 Speaker Mode, f = 1kHz, THD+N = 1% RL = 4Ω 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 RL = 32Ω Speaker Mode, f = 1kHz POUT = 100mW, RL = 8Ω Total Harmonic Distortion + Noise CC Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω OCL Headphone Mode, f = 1kHz POUT = 12mW, RL = 32Ω Speaker Mode, A-Wtg, Input Referred eN Noise CC Headphone Mode, A-Wtg, Input Referred OCL Headphone Mode, A-Wtg, Input Referred η Efficiency Speaker Mode RL = 8Ω 155 90 175 140 0.03 mW mW mW mW % 155 90 177 140 mW mW mW mW 1.75 1.06 2.2 1.35 W W W W Typical (Note 6) Limit (Notes 7, 8) Units (Limits) IDD Supply Current 8.5 3.6 4.7 0.15 10 10 12.4 5.5 6.5 2 25 60 mA (max) mA (max) mA (max) μA (max) mV (max) mV (max) ISD VOS Shutdown Supply Current Output Offset Voltage THD+N 0.02 % 0.03 47 10 11 84 % μV μV μV % 7 www.national.com LM49270 LM49270 Symbol Parameter Conditions Speaker Mode, f = 1kHz, VIN = 1Vp-p Xtalk Crosstalk CC Headphone Mode, f = 1kHz, VIN = 1Vp-p OCL Headphone Mode, f = 1kHz, VIN = 1Vp-p TON TOFF ZIN Turn-on Time Turn-off Time Input Impedance Maximum Gain Minimum Gain Maximum Gain, Speaker Mode AV Gain Minimum Gain, Speaker Mode Maximum Gain, Headphone Mode Minimum Gain, Headphone Mode Speaker Mode, VRIPPLE = 200mVp-p Sine f = 217Hz f = 1kHz Headphone Mode, VRIPPLE = 200mVp-p Sine, CC Mode f = 217Hz f = 1kHz Headphone Mode, VRIPPLE = 200mVp-p Sine, OCL Mode f = 217Hz f = 1kHz HPS(Th) Headphone Sense Threshold Detect Headphone Detect no Headphone Typical (Note 6) –85 –70 –58 43 100 23.5 210 30 –47 18 –59 Limit (Notes 7, 8) Units (Limits) dB dB dB ms ms kΩ kΩ dB dB dB dB 61 61 dB dB PSRR Power Supply Rejection Ratio 75 74 dB min 78 75 4.4 3 dB dB V (min) 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 20212908 20212909 THD+N vs Output Power CC Headphone Mode AV = 0dB, RL = 16Ω, f = 1kHz THD+N vs Output Power CC Headphone Mode AV = 0dB, RL = 32Ω, f = 1kHz 20212914 20212915 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 20212906 20212907 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 20212911 www.national.com 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 20212912 20212913 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 202129a2 202129a3 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 20212969 www.national.com 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 20212977 20212982 Power Dissipation vs Output Power CC Headphone Mode RL = 32Ω, f = 1kHz Output Power vs Supply Voltage Speaker Mode RL = 4Ω, f = 1kHz 20212983 20212971 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 20212996 20212997 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 20212930 20212931 Turn-Off CC Headphone Mode 20212932 www.national.com 16 LM49270 Application Information 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 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. TABLE 2. Device Address ADR X 0 1 A7 1 1 1 A6 1 1 1 A5 1 1 1 A4 1 1 1 A3 1 1 1 A2 0 0 0 A1 X 0 1 A0 0 0 0 TABLE 3. I2C Control Registers REG 0 1 2 Register Name Shutdown Control Headphone Gain Control Speaker Gain Control D7 0 0 1 D6 0 1 0 D5 — — — D4 — HP4 LS4 D3 HP3DSEL HP3 LS3 D2 LS3DSEL HP2 LS2 D1 OCL/CC HP1 LS1 D0 PWR_ON HP0 LS0 Note: OCL/CC = 1 selects OCL mode; OCL/CC = 0 selects cap coupled mode PWR_ON = 0 puts part in shutdown 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. 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. 20212991 FIGURE 2. I2C Bus Format 17 www.national.com LM49270 20212992 FIGURE 3. I2C Timing Diagram GENERAL AMPLIFIER FUNCTION 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. 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. 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: 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. 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 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. 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: PDMAX(CC) = VDD2/2π2RL 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 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). TABLE 4. Volume Control Volume Step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 LS4/HP4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 LS3/HP3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 LS2/HP2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 LS1/HP1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 LS0/HP0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 LS Gain (dB) –47 –36 –28.5 –22.5 –18 –15 –12 –9 –6 –3 –1.5 0 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19.5 21 22.5 24 25.5 27 28.5 30 HP Gain (dB) –59 –48 –46.5 –34.5 –30 –27 –24 –21 –18 –15 –13.5 –12 –10.5 –9 –7.5 –6 –4.5 –3 –1.5 0 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19 www.national.com LM49270 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) (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. 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 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. 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: f(–3dB) = 1/2πRINCIN (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. www.national.com 20 LM49270 Revision Table Rev 1.0 Date 12/19/06 Description 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. 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