LM4832 Digitally Controlled Tone and Volume Circuit with Stereo Audio Power Amplifier, Microphone Preamp Stage and National 3D Sound General Description The LM4832 is a monolithic integrated circuit that provides volume and tone (bass and treble) controls as well as a stereo audio power amplifier capable of producing 250 mW (typ) into 8Ω or 90 mW (typ) into 32Ω with less than 1.0% THD. In addition, a two input microphone preamp stage, with volume control, capable of driving a 1 kΩ load is implemented on chip. The LM4832 also features National’s 3D Sound circuitry which can be externally adjusted via a simple RC network. For maximum system flexibility, the LM4832 has an externally controlled, low-power consumption shutdown mode, and an independent mute for power and microphone amplifiers . Boomer ® audio integrated circuits were designed specifically to provide high quality audio while requiring few external components. Since the LM4832 incorporates tone and volume controls, a stereo audio power amplifier and a microphone preamp stage, it is optimally suited to multimedia monitors and desktop computer applications. Key Specifications n Output Power at 10% into: 8Ω 32Ω n THD + N at 75 mW into 32Ω at 1 kHz n Microphone Input Referred Noise 350 mW(typ) 100 mW(typ) 0.5%(max) 7 µV(typ) n Supply Current 13 mA(typ) n Shutdown Current 4 µA(max) Features n n n n n n Independent Left and Right Output Volume Controls Treble and Bass Control National 3D Sound I2C Compatible Interface Two Microphone Inputs with Selector Software Controlled Shutdown Function Applications n Multimedia Monitors n Portable and Desktop Computers Block Diagram Connection Diagram DS100014-2 DS100014-1 FIGURE 1. LM4832 Block Diagram Top View Order Number LM4832N, LM4832M See NS Package Number N28B for DIP See NS Package Number M28B for SOIC Boomer ® is a registered trademark of National Semiconductor Corporation. © 1998 National Semiconductor Corporation DS100014 www.national.com LM4832 Digitally Controlled Tone and Volume Circuit with Stereo Audio Power Amplifier, Microphone Preamp Stage and National 3D Sound February 1998 Absolute Maximum Ratings (Note 2) Infrared (15 sec.) 6.0V θJC (typ)—N28B 21˚C/W −65˚C to +150˚C θJA (typ)—N28B 62˚C/W −0.3V to VDD +0.3V θJC (typ)—M28B 15˚C/W θJA (typ)—M28B 69˚C/W Supply Voltage Storage Temperature Input Voltage 220˚C See AN-450 ″Surface Mounting and their Effects on Product Reliability″ for other methods of soldering surface mount devices. If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Power Dissipation (Note 3) Internally limited ESD Susceptibility (Note 4) 2000V ESD Susceptibility (Note 5) 250V Junction Temperature Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX 150˚C Soldering Information Small Outline Package Vapor Phase (60 sec.) −40˚C ≤ TA ≤ 85˚C 4.5 ≤ VDD ≤ 5.5V Supply Voltage 215˚C Electrical Characteristics for Entire IC(Notes 1, 2) The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C. LM4832 Symbol VDD Parameter Supply Voltage Conditions Typical (Note 6) VIN = 0V, IO = 0A Limit (Note 7) Units (Limits) 4.5 V (min) 5.5 V (max) IDD Quiescent Power Supply Current 13 21 mA (max) ISD Shutdown Current 2.5 9 µA (max) 1 −15 dB (max) dB (min) INPUT ATTENUATORS AR Attenuator Range Attenuation at 0 dB Setting Attenuation at −14 dB Setting AS Step Size 0 dB to −14 dB ET 2 dB Gain Step Size Error 0.1 dB (max) Channel to Channel Tracking Error 0.15 dB (max) BASS CONTROL AR Bass Control Range f = 100 Hz, VIN = 0.25V ± 12 −14 dB (min) 14 dB (max) AS Bass Step Size 2 dB ESE Bass Step Size Error 0.5 dB (max) ET Bass Tracking Error 0.15 dB (max) TREBLE CONTROL AR Treble Control Range fIN = 10 kHz, VIN = 0.25V ± 12 −13 dB (min) 13 dB (max) AS Treble Step Size 2 dB ESE Treble Step Size Error 0.1 dB (max) ET Treble Tracking Error 0.15 dB (max) OUTPUT ATTENUATORS AR AS ET Attenuator Range Step Size Gain at +20 dB Setting Attenuation at −40 dB Setting +20 dB to −40 dB 21 dB (max) −42 dB (min) 2 dB Step Size Error 0.1 dB (max) Channel to Channel Tracking Error 0.1 dB (max) AUDIO PATH VOS www.national.com Output Offset Voltage VIN = 0V 3 2 50 mV (max) Electrical Characteristics for Entire IC(Notes 1, 2) (Continued) The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C. LM4832 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) AUDIO PATH PO THD+N Output Power Total Harmonic Distortion+Noise THD = 1.0% (max), f = 1 kHz, All controls at 0dB RL = 8Ω 250 RL = 32Ω 95 mW (min) 75 mW (min) All Controls at 0 dB, THD = 10%, f = 1 kHz RL = 8Ω 350 mW PO = 200 mW, RL = 8Ω 0.15 % PO = 75 mW, RL = 32Ω 0.11 % VO = 1 Vrms, RL = 10Ω 0.08 % PSRR Power Supply Rejection Ratio CB = 1 µF, f = 100 Hz, VRIPPLE = 100 mVrms, All Controls at 0 dB Setting 45 dB AM Mute Attenuation f = 1 kHz, VIN = 1V −75 dB XTALK Cross Talk PO = 200 mW, RL = 8Ω, All controls at 0 dB setting, f = 1 kHz Left to Right −85 dB Right to Left −72 dB MICROPHONE PREAMP AND VOLUME CONTROL AV Preamp Gain AR Attenuator Range AS Step Size 0 dB Gain 0 −1, 1 dB +20 dB Gain 20 19, 21 dB +30 dB Gain 30 29, 31 dB 20 dB (max) −43 dB (min) Gain at +18 dB Setting Attenuation at −42 dB Setting 0 dB to −42 dB Step Size Error 3 dB 0.4 dB (max) VSWING Output Voltage Swing f = 1 kHz, THD < 1.0%, RL = 1 kΩ 1.7 Vrms ENO Input Referred Noise A-Weighted, Attenuator at 0 dB 7 µV (min) PSRR Power Supply Rejection Ratio f = 100 Hz, VRIPPLE = 100 mVrms, CB = 1 µF 35 dB AM Mute Attenuation −90 dB XTALK Cross Talk Power Amp PO = 200 mW, f = 1 kHz −90 dB THD+N Total Harmonic Distortion Plus Noise 0 dB Setting 0.03 % +20 dB Gain 0.03 % +30 dB Gain 0.04 % All controls at 0 dB, f = 1 kHz, VO = 1V I2C BUS TIMING fMAX Maximum Bus Frequency 400 kHz TSTART:HOLD Start Signal: Hold Time before Clock/Data Transitions 0.6 µs TD;SETUP Data Setup Time 0.1 µs TC;HIGH Minimum High Clock Duration 0.6 µs TC;LOW Minimum Low Clock Duration 1.3 µs TSTOP;SETUP Stop Signal: Setup Time before Clock/Data Transitions 0.6 µs 1.5 V (max) I2C BUS INPUT AND OUTPUT VIL Input Low Voltage 3 www.national.com Electrical Characteristics for Entire IC(Notes 1, 2) (Continued) The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25˚C. LM4832 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) I2C BUS INPUT AND OUTPUT VIH Input High Voltage IIN Input Current VO 3 V (min) Output Voltage—SDA Acknowledge 0.4 V (max) VOL External Power Amp Disable Low 0.4 V (max) VOH External Power Amp Disable High 4 V (min) 0.15 µA Note 1: All voltages are measured with respect to the ground pins, unless otherwise specified. All specifications are tested using the typical applicationas shown in Figure 1. 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.For the LM4832, TJMAX = 150˚C, and the typical junction-to-ambient thermal resistance, when board mounted, is 69˚C/W assuming the M28B package. Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 5: Machine Model, 220 pF–240 pF discharged through all pins. Note 6: Typicals are measured at 25˚C and represent the parametric norm. Note 7: Limits are guaranteed that all parts are tested in production to meet the stated values. Typical Application Circuit DS100014-3 FIGURE 2. Typical Application Circuit www.national.com 4 Pin Description LEFT 3D (1) RIGHT 3D (28) BYPASS (2) An external RC network is connected across these pins. This function provides left-right channel cross coupling and cancellation to create an enhanced stereo channel separation effect. A 0.1 µF capacitor is placed between this pin and ground to provide an AC ground for the internal half-supply voltage reference. The capacitor at this pin affects “click-pop” and THD performance. Turn-on and turn-off times are also determined by this capacitor. Refer to the Application Information section for more information. POWER AMP OUT LEFT (3) RIGHT (26) These outputs are intended to drive 8Ω speakers or 32Ω headphones. These outputs should be AC-coupled to the loads. Refer to the Application Information section for more information. POWER GND (4) This pin provides the high current return for the power output stage MOSFETs and digital circuitry. LOOP OUT (8, 21) LOOP IN (5, 24) These pins allow an external signal processor access to the stereo signal. Please see the Application Information section for more information. TONE OUT (6, 23) These pins are connected to the tone control op amp outputs and drive the power amplifier inputs. Refer to the Application Information section for more information. TONE IN (7, 22) These pins are connected to the inputs of the tone control op amps. A capacitor between the Tone In and Tone Out pins sets the frequency response of the tone functions. Please refer to the Application Information section for more information. INPUTS (9, 20) These pins are the stereo inputs for the LM4832. These pins should be AC-coupled to the input signals. ANALOG GND (10) This pin is the AC analog ground for the line level AC signal inputs. MIC INPUTS (11, 12) These pins are the two independent selectable microphone inputs. These pins should be AC-coupled. MIC OUT (14) This pin is the output for the microphone amplifier and should be AC-coupled to the load. VDD (13, 25) These pins are for the 5V supply. These pins should be separately bypassed by 0.1 µF, or higher, film capacitors. The 5V supply should be bypassed by a 10 µF, or higher, tantalum or aluminum electrolytic capacitor. ADDRESS BITS (15, 16) These pins are used to determine the I2C address for the LM4832. 5 CLOCK (17) This pin is the input for the I2C clock signal. DATA (18) This pin is the input for the I2C data signal. GENERAL PURPOSE OUTPUT (19) This pin provides a general purpose TTL/CMOS output. Please refer to the Application Information section for more information. RESET (27) This pin is a TTL/CMOS input which is used to reset the chip logic and states. www.national.com Typical Performance Characteristics THD+N vs Frequency, 8Ω THD+N vs Frequency, 32Ω THD+N vs Frequency, 1 kΩ DS100014-4 THD+N vs Output Power DS100014-5 THD+N vs Output Power THD+N vs Output Power DS100014-7 Power Amplifier Crosstalk DS100014-8 Power Amplifier Noise Floor DS100014-9 Power Amplifier Attenuation vs Frequency DS100014-10 www.national.com DS100014-6 DS100014-11 6 DS100014-12 Typical Performance Characteristics Power Supply Rejection Ratio (Continued) Power Dissipation vs Output Power DS100014-14 DS100014-13 Mic Amplifer Crosstalk from Power Amplifier Power Derating Curve Mic Amplifier Noise Floor Mic Amplifier Attenuation vs Frequency DS100014-16 Mic Amplifier Gain vs Frequency DS100014-15 DS100014-17 Mic Amplifier THD+N vs Frequency DS100014-19 Loop-out THD+N vs Frequency DS100014-20 7 DS100014-18 DS100014-21 www.national.com Typical Performance Characteristics Bass Response vs Frequency (Continued) Treble Response vs Frequency Bass and Treble Response vs Frequency DS100014-22 DS100014-23 DS100014-24 Supply Current vs Temperature DS100014-25 Timing Diagram DS100014-26 FIGURE 3. I2C Bus Format www.national.com 8 Timing Diagram (Continued) DS100014-27 See Electrical Characteristics section fortiming specifications FIGURE 4. I2C Timing Diagram 9 www.national.com Truth Tables SOFTWARE SPECIFICATION Chip Address MSB 1 LSB 0 0 0 0 *E.C. *E.C. 0 *E.C. = Externally Configuarable Data Bytes (Brief Description) MSB LSB Function 0 0 0 X X D2 D1 D0 Input Volume Control 0 0 1 X D3 D2 D1 D0 Bass Control 0 1 0 X D3 D2 D1 D0 Treble Control 0 1 1 D4 D3 D2 D1 D0 Right Output Vol./Mute 1 0 0 D4 D3 D2 D1 D0 Left Output Vol./Mute 1 0 1 X D11 D10 D01 D00 Mic Input and Gain 1 1 0 D4 D3 D2 D1 D0 Microphone Volume 1 1 1 D40 D30 D20 D10 D00 General Control Input Volume Control MSB LSB Attenuation (dB) 0 0 0 X X 0 0 0 0 0 0 0 X X 0 0 1 −2 0 0 0 X X 0 1 0 −4 0 0 0 X X 0 1 1 −6 0 0 0 X X 1 0 0 −8 0 0 0 X X 1 0 1 −10 0 0 0 X X 1 1 0 −12 0 0 0 X X 1 1 1 −14 X X 0 0 0 Input Volume Control at 0 dB Attenuation Input Volume Control Power Up State Bass Control MSB LSB Level (dB) 0 0 1 X 0 0 0 0 −12 0 0 1 X 0 0 0 1 −10 0 0 1 X 0 0 1 0 −8 0 0 1 X 0 0 1 1 −6 0 0 1 X 0 1 0 0 −4 0 0 1 X 0 1 0 1 −2 0 0 1 X 0 1 1 0 0 0 0 1 X 0 1 1 1 2 0 0 1 X 1 0 0 0 4 0 0 1 X 1 0 0 1 6 0 0 1 X 1 0 1 0 8 0 0 1 X 1 0 1 1 10 0 0 1 X 1 1 0 0 12 X 0 1 1 0 Bass Control is Flat Bass Control Power Up State www.national.com 10 Truth Tables (Continued) Treble Control MSB LSB Level (dB) 0 1 0 X 0 0 0 0 −12 0 1 0 X 0 0 0 1 −10 0 1 0 X 0 0 1 0 −8 0 1 0 X 0 0 1 1 −6 0 1 0 X 0 1 0 0 −4 0 1 0 X 0 1 0 1 −2 0 1 0 X 0 1 1 0 0 0 1 0 X 0 1 1 1 2 0 1 0 X 1 0 0 0 4 0 1 0 X 1 0 0 1 6 0 1 0 X 1 0 1 0 8 0 1 0 X 1 0 1 1 10 0 1 0 X 1 1 0 0 12 X 0 1 1 0 Treble Control is Flat Treble Control Power Up State Left Volume Control MSB LSB Function 1 0 0 0 0 0 0 0 20 1 0 0 0 0 0 0 1 18 1 0 0 ... ... ... ... ... ... 1 0 0 1 1 1 0 1 −38 1 0 0 1 1 1 1 0 −40 1 0 0 1 1 1 1 1 Left Channel Mute Left Volume Control Power Up State 1 1 1 1 1 Left Channel is Muted General Control MSB LSB Function 1 1 1 0 Chip On 1 1 1 1 Chip Shutdown 1 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 1 1 1 1 0 1 1 1 1 General Control Power Up State 0 G.P.O. Output Low G.P.O. Output High 0 Stereo Enhance Off 1 Stereo Enhance On Stereo Operation Mono Force On External Loop Disable External Loop Enable 0 0 0 11 0 www.national.com Truth Tables (Continued) Right Volume Control MSB LSB Level (dB) 0 1 1 0 0 0 0 0 20 0 1 1 0 0 0 0 1 18 0 1 1 ... ... ... ... ... ... 0 1 1 1 1 1 0 0 −38 0 1 1 1 1 1 1 0 −40 0 1 1 1 1 1 1 1 Right Channel Mute 1 1 1 1 1 Right Channel Is Muted Right Volume Control Power Up State Microphone Input Selection and Gain MSB LSB Function 1 0 1 X 0 0 Mic Input 1 1 0 1 X 0 1 Mic Input 2 1 0 1 X 1 X Mic Input 1 and 2 1 0 1 X 0 0 Mic Gain (+0 dB) 1 0 1 X 0 1 Mic Gain (+20 dB) 1 0 1 X 1 0 Mic Input Sel. and Gain Power Up State X 1 0 0 Mic Gain (+30 dB) 0 Mic 1 is selected with a +30 dB gain Microphone Volume Control MSB LSB Function 1 1 0 0 0 0 0 0 18 1 1 0 0 0 0 0 1 15 1 1 0 ... ... ... ... ... ... 1 1 0 1 0 1 0 0 −42 1 1 0 1 0 1 0 1 Microphone Muted Mic Volume Control Power Up State 1 0 1 0 1 Microphone Muted www.national.com 12 bypass pin has reached its half supply voltage, 1/2 VDD. As soon as the bypass node is stable, the device will become fully operational. Application Information GROUNDING In order to achieve the best possible performance, certain grounding techniques should be followed. All input reference grounds should be tied with their respective source grounds and brought back to the power supply ground separately from the output load ground returns. These input grounds should also be tied in with the half-supply bypass ground. Bringing the ground returns for the output loads back to the supply separately will keep large signal currents from interfering with the stable AC input ground references. Although the bypass pin current source cannot be modified, the size of the bypass capacitor, CB, can be changed to alter the device turn-on time and the amount of “click and pop”. By increasing CB, the amount of turn-on pop can be reduced. However, the trade-off for using a larger bypass capacitor is an increase in the turn-on time for the device. Reducing CB will decrease turn-on time and increase “click and pop”. If CB is too small, the LM4832 can develop a low-frequency oscillation (“motorboat”) when used at high gains. There is a linear relationship between the size of CB and the turn-on time. Some typical turn-on times for different values of CB are: LAYOUT As stated in the Grounding section, placement of ground return lines is critical for maintaining the highest level of system performance. It is not only important to route the correct ground return lines together, but also important to be aware of where those ground return lines are routed in conjunction with each other. The output load ground returns should be physically located as far as reasonably possible from low signal level lines and their ground return lines. Critical signal lines are those relating to the microphone amplifier section, since these lines generally work at very low signal levels. Cb TON 0.01 µF 20 ms 0.1 µF 200 ms 0.22 µF 420 ms In order to eliminate “click and pop”, all capacitors must be discharged before turn-on. Rapid on/off switching of the device or shutdown function may cause the “click and pop” circuitry to not operate fully, resulting in increased “click and pop” noise. The output coupling cap, CO, is of particular concern. This capacitor discharges through an internal 20 kΩ resistor. Depending on the size of CO, the time constant can be quite large. To reduce transients, an external 1 kΩ–5 kΩ resistor can be placed in parallel with the internal 20 kΩ resistor. The tradeoff for using this resistor is an increase in quiescent current. SUPPLY BYPASSING As with all op amps and power op amps, the LM4832 requires the supplies to be bypassed to avoid oscillation. To avoid high frequency instabilities, a 0.1 µF metallized-film or ceramic capacitor should be used to bypass the supplies as close to the chip as possible. For low frequency considerations, a 10 µF or greater tantalum or electrolytic capacitor should be paralleled with the high frequency bypass capacitor. If power supply bypass capacitors are not sufficiently large, the current in the power supply leads, which is a rectified version of the output current, may be fed back into internal circuitry. This internal feedback signal can cause high frequency distortion and oscillation. If power supply lines to the chip are long, larger bypass capacitors could be required. Long power supply leads have inductance and resistance associated with them, that could prevent peak low frequency current demands from being met. The extra bypass capacitance will reduce the peak current requirements from the power supply lines. COUPLING CAPACITORS Because the LM4832 is a single supply circuit, all audio signals must be capacitor coupled to the chip to remove the 2.5 VDC bias. All audio inputs have 20 kΩ input impedances, so the AC-coupling capacitor will create a high-pass filter with f−3dB = 1/(2π*20 kΩ*CIN). The amplifier outputs also need to be AC-coupled to the loads.The high-pass filter is comprised of the output load and the coupling capacitor,where the filter cutoff is at f−3dB = 1/(2π*RLOAD*COUT). POWER AMPLIFIER The power amplifiers in the LM4832 are designed to drive 8Ω or 32Ω loads at 200 mW (continuous) and 75 mW (continuous), respectively, with 1% THD+N. As shown in the Typical Performance Characteristics, the power amplifiers typically drive 4Ω loads at 350 mW, but with a slight increase in high-frequency THD. As discussed above, these outputs should be AC-coupled to the output load. POWER-UP STATUS On power-up or after a hard reset, the LM4832 registers will be initialized with the default values listed in the truth tables. By default, the LM4832 power and microphone outputs are muted, the tone controls are all flat, National 3D Enhance is off, the chip is in stereo mode, and the microphone input 1 is selected with +30 dB of gain. MICROPHONE AMPLIFIER CLICK AND POP CIRCUITRY The LM4832 contains circuitry to minimize turn-on transients or “click and pops”. In this case, turn-on refers to either power supply turn-on or the device coming out of shutdown mode. When the deviceis turning on, the amplifiers are internally configured as unity gain buffers. An internal current source charges the bypass capacitor on the bypass pin. Both the inputs and outputs ideally track the voltage at the bypass pin. The device will remain in buffer mode until the The microphone preamplifier is intended to amplify low-level signals for signal conditioning. The microphone inputs can be directly connected to microphone networks. The microphone amplifier has enough output capability to drive a 1 kΩ load. All microphone inputs and outputs must be ACcoupled. 13 www.national.com Application Information An external RC network, shown in Figure 3, is required to enable the effect. The amount of the effect is set by the 20 kΩ resistor. A 0.1 µF capacitor is used to reduce the effect at frequencies below 80 Hz. Decreasing the resistor size will make the 3D effect more pronounced and decreasing the capacitor size will raise the cutoff frequency for the effect. The 680 kΩ resistor across the 0.1 µF capacitor reduces switching noise by discharging the capacitor when the effect is not in use. (Continued) I2C INTERFACE The LM4832 uses a serial bus, which conforms to the I2C protocol, to control the chip’s functions with two wires: clock and data. The clock line is uni-directional. The data line is bidirectional(open-collector) with a pullup resistor (typically 10 kΩ).The maximum clock frequency specified by the I2C standard is 400 kHz. In this discussion, the master is the controlling microcontroller and the slave is the LM4832. The I2C address for the LM4832 is determined using the Address Bit 1 and Address Bit 2 TTL/CMOS inputs on the chip. The LM4832’s four possible I2C chip addresses are of the form 10000X2X10 (binary), where the X2 and X1bits are determined by the voltage levels at the Address Bit 2 and Address Bit 1 pins, respectively. If the I2C interface is used to address a number of chips in a system and the LM4832’s chip address can be changed to avoid address conflicts. DS100014-28 The timing diagram for the I2C is shown in Figure 2. The data is latched in on the stable high level of the clock and the data line should be held high when not in use. The timing diagram is broken up into six major sections: The “start” signal is generated by lowering the data signal while the clock signal is high. The start signal will alert all devices attached to the I2C bus to check the incoming address against their own chip address. The 8-bit chip address is sent next, most significant bit first. Each address bit must be stable while the clock level is high. After the last bit of the address is sent, the master checks for the LM4832’s acknowledge. The master releases the data line high (through a pullup resistor). Then the master sends a clock pulse. If the LM4832 has received the address correctly, then it holds the data line low during the clock pulse. If the data line is not low, then the master should send a “stop” signal (discussed later) and abort the transfer. The 8 bits of data are sent next, most significant bit first. Each data bit should be valid while the clock level is stable high. After the data byte is sent, the master must generate another acknowledge to see if the LM4832 received the data. If the master has more data bytes to send to the LM4832, then the master can repeat the previous two steps until all data bytes have been sent. The “stop” signal ends the transfer. To signal “stop”, the data signal goes high while the clock signal is high. FIGURE 5. 3D Effect Components TONE CONTROL RESPONSE Bass and treble tone controls are included in the LM4832. The tone controls use two external capacitors for each stereo channel. Each has a corner frequency determined by the value of C2 and C3 (see Figure 4) and internal resistors in the feedback loop of the internal tone amplifier. Typically, C2 = C3 and for 100 Hz and 10 kHz corner frequencies, C2 = C3 = 0.0082 µF. Altering the ratio between C2 and C3, changes the midrange gain. For example, if C2 = 2(C3), then the frequency response will be flat at 20 Hz and 20 kHz, but will have a 6 dB peak at 1 kHz. With C = C2 = C3, the treble turn-over frequency is nominally fTT = 1/(2πC(14 kΩ)) and the bass turn-over frequency is nominally fBT = 1/(2πC(30.4 kΩ)), when maximum boost is chosen. The inflection points (the frequencies where the boost or cut is within 3 dB of the final value) are, for treble and bass respectively, fTI = 1/(2πC(1.9 kΩ)) fBI = 1/(2πC(169.6 kΩ)) Increasing the values of C2 and C3 decreases the turnover and inflection frequencies: i.e., the Tone Control Response Curves shown in Typical Performance Section will shift left when C2 and C3 are increased and shift right when C2 and C3 are decreased. With C2 = C3 = 0.0082 µF, 2 dB steps are achieved at 100 Hz and 10 kHz. Changing C2 and C3 to 0.01 µF shifts the 2 dB step frequency to 72 Hz and 8.3 kHz.If the tone control capacitors’ size is decreased these frequencies will increase.With C2 = C3 = 0.0068 µF the 2 dB steps take place at 130 Hz and 11.2 kHz. 3D AUDIO ENHANCEMENT The LM4832 has a 3D audio enhancement effect that helps improve the apparent stereo channel separation when, because of cabinet or equipment limitations, the left and right speakers are closer to each other than optimal. www.national.com 14 Application Information (Continued) DS100014-29 FIGURE 6. Tone Control Diagram channel (rms) power amplifier with mute. AC-coupling capacitors must be used to remove the DC bias present between the LM4832 outputs and the external power amplifier inputs. Prior to placing any of the preamp circuitry in shutdown, the General Purpose Output should be used to disable the external power amplifier.This will prevent any shutdown transients in the preamp circuitry from being amplified by the external power amplifier. GENERAL PURPOSE OUTPUT PIN The General Purpose Output pin is intended to be used as a control signal for other devices, such as an external power amplifier. This pin is controlled through the I2C interface and is not relatedto any other functions within the LM4832. Refer to the Truth Tables section for the proper I2C data bits to utilize this function. Figure 7 shows an example of using the General Purpose Output to interface with an external power amp. In this case, the external power amp is the LM4755 stereo 10 watt per DS100014-30 10W/ch System with I2C Controlled Tone,Volume and 3D Sound Since the Loop In pin goes directly to the input of a CMOS amplifier, the input impedance is very high. The Loop Out pin is driven by the input attenuation amplifier, which is capable of driving impedances as low as 1 kΩ. LOOP IN/OUT PINS The Loop In and Loop Out pins are used when an application requires a special function to be performed on the audio signal. As shown in Figure 7, the audio signal is taken from the Loop Out pin and sent to an external signal processor. After the signal is processed externally, it is fed back into the Loop In pin. An example of where this functionality would be used is computer speakers. The external loop could be used to provide bass boost to counteract the speaker’s natural or baffleinduced rolloff. 15 www.national.com Application Information (Continued) DS100014-31 LM4832 SAMPLE LAYOUT LAYOUT PARTS LIST LAYOUT PARTS LIST Name Name Type Quantity COUT 1000 µF, elec., Digikey #P6205 4 CMOUT 47 µF, elec., Digikey #P5202 1 CS 0.33 µF, film, Digikey #P4669 3 CTONE 8200 pF, ceramic, Digikey #P4823 4 Type Quantity Connectors: Capacitors: Banana Jack CLIN, CMIN, CIN 1 µF, film, Digikey #E1105 6 CB 0.33 µF, film, Digikey #EF1334 1 C1 0.1 µF, film, Digikey #EF1104 1 20 kΩ, 1/4W 1 R2 680 kΩ, 1/4W 1 RDATA 1 kΩ, 1/4W 1 RGND 100Ω, 1/4W 1 RPD 100 kΩ, 1/4W 1 Mouser #164-6218 Red Mouser #164-6218 3 3 RCA Jack Mouser #16PJ097 7 Stereo Headphone Shogyo #JJ-0357-3RT 1 Mono Miniplug Shogyo #JJ-0357-B 2 36-pin Digikey #1036RF 1 Centronics LAYOUT DESCRIPTION The layout given in the following pages is meant to be connected to a PC by a parallel port (printer) cable. The board is controlled by software for a Windows PC. The parallel cable must be the standard type used for hooking up a printer to a PC: one end is a DB-25 connector andthe other is a 36 pin Centronics connector. Banana connections are provided for VDD, ground, and amplifier outputs. Amplifier outputs are also routed to a stereo headphone jack. RCA connections are provided for amplifier inputs, loop in, loop out, and microphone out. Mono miniplug connectors are provided for microphone inputs. If required, microphones can be biased using the resistors RMIC1 and RMIC2. Resistors (all resistors: Digikey #(Value)QBK): R1 Black This layout is set up to allow the use of the internal tonecontrol circuitry or the external loop. The jumper next to each CLIN capacitor controls which route the signal should take. www.national.com 16 DS100014-32 Typical Application PCB Layout (All Layers) 17 www.national.com DS100014-33 Typical Application PCB Layout (Silkscreen Layer) www.national.com 18 DS100014-34 Typical Application PCB Layout (Bottom Layer) 19 www.national.com DS100014-35 Typical Application PCB Layout (Top Layer) www.national.com 20 Physical Dimensions inches (millimeters) unless otherwise noted 28-Lead SOIC Package (M28B) Order Number LM4832M NS Package Number M28B for SOIC 21 www.national.com LM4832 Digitally Controlled Tone and Volume Circuit with Stereo Audio Power Amplifier, Microphone Preamp Stage and National 3D Sound Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 28-Lead Dual-In-Line Package (N28B) Order Number LM4832N NS Package Number N28B for DIP LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component in any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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