LM4910LQ/NOPB

LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 LM4910 Output Capacitor-less Stereo 35mW Headphone Amplifier Check for Samples: LM4910 FEATURES • 1 • 2 • • • • • Eliminates headphone amplifier output coupling capacitors Eliminates half-supply bypass capacitor Advanced pop & click circuitry eliminates noises during turn-on and turn-off Ultra-low current shutdown mode Unity-gain stable 2.2V - 5.5V operation Available in space-saving MSOP, LLP, and SOIC packages APPLICATIONS • • • • Mobile Phones PDAs Portable electronics devices Portable MP3 players DESCRIPTION The LM4910 is an audio power amplifier primarily designed for headphone applications in portable device applications. It is capable of delivering 35mW of continuous average power to a 32Ω load with less than 1% distortion (THD+N) from a 3.3VDC power supply. The LM4910 utilizes a new circuit topology that eliminates output coupling capacitors and half-supply bypass capacitors. The LM4910 contains advanced pop & click circuitry which eliminates noises caused by transients that would otherwise occur during turn-on and turn-off. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. Since the LM4910 does not require any output coupling capacitors, half-supply bypass capacitors, or bootstrap capacitors, it is ideally suited for low-power portable applications where minimal space and power consumption are primary requirements. The LM4910 features a low-power consumption shutdown mode, activated by driving the shutdown pin with logic low. Additionally, the LM4910 features an internal thermal shutdown protection mechanism. The LM4910 is also unity-gain stable and can be configured by external gain-setting resistors. Table 1. Key Specifications VALUE UNIT PSRR at f = 217Hz 65 dB (typ) Power Output at VDD = 3.3V, RL = 32Ω, and THD ≤ 1% 35 mW (typ) Shutdown Current 0.1 µA (typ) 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2004–2007, Texas Instruments Incorporated LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Typical Application Figure 1. Typical Audio Amplifier Application Circuit Connection Diagram Figure 2. MSOP/SO Package Top View Figure 3. MSOP Marking Top View G - Boomer Family C2 - LM4910MM Figure 4. SO Marking Top View TT - Die Traceability Bottom 2 lines - Part Number 2 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Figure 5. LLP Package Top View These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings Supply Voltage (1) (2) 6.0V −65°C to +150°C Storage Temperature Input Voltage Power Dissipation -0.3V to VDD + 0.3V (3) ESD Susceptibility Pin 6 ESD Susceptibility (5) ESD Susceptibility (6) Internally Limited (4) 10kV 2000V 200V Junction Temperature 150°C Thermal Resistance (1) (2) (3) (4) (5) (6) θJC (MSOP) 56°C/W θJA (MSOP) 190°C/W θJC (SOP) 35°C/W θJA (SOP) 150°C/W θJC (LQ) 57°C/W θJA (LQ) 140°C/W 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. If the product is in shutdown mode and VDD exceeds 6V (to a max of 8V VDD) then most of the excess current will flow through the ESD protection circuits. If the source impedance limits the current to a max of 10ma then the part will be protected. If the part is enabled when VDD is above 6V circuit performance will be curtailed or the part may be permanently damaged. 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 LM4910, see power derating currents for more information. Human body model, 100pF discharged through a 1.5kΩ resistor, Pin 6 to ground. Human body model, 100pF discharged through a 1.5kΩ resistor. Machine Model, 220pF-240pF discharged through all pins. Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX −40°C ≤ T A ≤ 85°C Supply Voltage (VDD) 2.2V ≤ VCC ≤ 5.5V Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 3 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 Electrical Characteristics VDD = 3.3V www.ti.com (1) (2) The following specifications apply for VDD = 3.3V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25°C. Symbol Parameter Conditions LM4910 Typ (3) Limit Units (Limits) (4) (5) IDD Quiescent Power Supply Current VIN = 0V, 32Ω Load 3.5 6 mA (max) ISD Standby Current VSHUTDOWN = GND 0.1 1.0 µA (max) VOS Output Offset Voltage 5 30 mV (max) PO Output Power THD = 1% (max); f = 1kHz 35 30 mW (min) THD+N Total Harmonic Distortion + Noise PO = 30mWrms; f = 1kHz 0.3 % PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p sinewave Input terminated with 10Ω to ground 65 (f = 217Hz) 65 (f = 1kHz) dB VIH Shutdown Input Voltage High 1.5 V (min) VIL Shutdown Input Voltage Low 0.4 V (max) (1) (2) (3) (4) (5) 4 All voltages are measured with respect to the GND pin unless otherwise specified. 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. Typicals are measured at 25°C and represent the parametric norm. Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Electrical Characteristics VDD = 3V (1) (2) The following specifications apply for VDD = 3V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25°C. Symbol Parameter Conditions LM4910 Typ (3) Limit Units (Limits) (4) (5) IDD Quiescent Power Supply Current VIN = 0V, 32Ω Load 3.3 6 mA (max) ISD Standby Current VSHUTDOWN = GND 0.1 1.0 µA (max) VOS Output Offset Voltage 5 30 mV (max) PO Output Power THD = 1% (max); f = 1kHz 30 25 mW (min) THD+N Total Harmonic Distortion + Noise PO = 25mWrms; f = 1kHz 0.3 % PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p sinewave Input terminated with 10Ω to ground 65 (f = 217 Hz) 65 (f = 1kHz) dB VIH Shutdown Input Voltage High 1.5 V (min) VIL Shutdown Input Voltage Low 0.4 V (max) (1) (2) (3) (4) (5) All voltages are measured with respect to the GND pin unless otherwise specified. 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. Typicals are measured at 25°C and represent the parametric norm. Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 5 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 Electrical Characteristics VDD = 2.6V www.ti.com (1) (2) The following specifications apply for VDD = 2.6V, AV = 1, and 32Ω load unless otherwise specified. Limits apply to TA = 25°C. Symbol Parameter Conditions LM4910 Typ (3) Limit Units (Limits) (4) (5) IDD Quiescent Power Supply Current VIN = 0V, 32Ω Load 3.0 mA (max) ISD Standby Current VSHUTDOWN = GND 0.1 µA (max) VOS Output Offset Voltage 5 mV (max) PO Output Power THD = 1% (max); f = 1kHz 13 mW THD+N Total Harmonic Distortion + Noise PO = 10mWrms; f = 1kHz 0.3 % PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p sinewave Input terminated with 10Ω to ground 55 (f = 217Hz) 55 (f = 1kHz) dB (1) (2) (3) (4) (5) All voltages are measured with respect to the GND pin unless otherwise specified. 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. Typicals are measured at 25°C and represent the parametric norm. Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. External Components Description (Figure 1) Components 6 Functional Description 1. RI Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high-pass filter with Ci at fc = 1/(2πRiCi). 2. CI Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a high-pass filter with Ri at fc = 1/(2πRiCi). Refer to the section Proper Selection of External Components, for an explanation of how to determine the value of Ci. 3. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri. 4. CS 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. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Typical Performance Characteristics THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency THD+N vs Frequency THD+N vs Output Power THD+N vs Output Power Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 7 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Typical Performance Characteristics (continued) 8 THD+N vs Output Power THD+N vs Output Power THD+N vs Output Power THD+N vs Output Power Output Power vs Load Resistance Output Power vs Load Resistance Output Power vs Load Resistance Output Power vs Supply Voltage Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Typical Performance Characteristics (continued) Output Power vs Supply Voltage Power Dissipation vs Output Power Power Dissipation vs Output Power Power Dissipation vs Output Power Channel Separation Power Supply Rejection Ratio Power Supply Rejection Ratio Power Supply Rejection Ratio Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 9 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Typical Performance Characteristics (continued) Open Loop Frequency Response Noise Floor Frequency Response vs Input Capacitor Size Supply Current vs Supply Voltage Application Information ELIMINATING OUTPUT COUPLING CAPACITORS Typical single-supply audio amplifiers that drive single-ended (SE) headphones use a coupling capacitor on each SE output. This output coupling capacitor blocks the half-supply voltage to which the output amplifiers are typically biased and couples the audio signal to the headphones. The signal return to circuit ground is through the headphone jack's sleeve. The LM4910 eliminates these output coupling capacitors. Amp3 is internally configured to apply a bandgap referenced voltage (VREF = 1.58V) to a stereo headphone jack's sleeve. This voltage matches the quiescent voltage present on the Amp1 and Amp2 outputs that drive the headphones. The headphones operate in a manner similar to a bridge-tied-load (BTL). The same DC voltage is applied to both headphone speaker terminals. This results in no net DC current flow through the speaker. AC current flows through a headphone speaker as an audio signal's output amplitude increases on the speaker's terminal. The headphone jack's sleeve is not connected to circuit ground. Using the headphone output jack as a line-level output will place the LM4910's bandgap referenced voltage on a plug's sleeve connection. This presents no difficulty when the external equipment uses capacitively coupled inputs. For the very small minority of equipment that is DC-coupled, the LM4910 monitors the current supplied by the amplifier that drives the headphone jack's sleeve. If this current exceeds 500mAPK, the amplifier is shutdown, protecting the LM4910 and the external equipment. ELIMINATING THE HALF-SUPPLY BYPASS CAPACITOR Typical single-supply audio amplifers are normally biased to 1/2VDD in order to maximize the output swing of the audio signal. This is usually achieved with a simple resistor divider network from VDD to ground that provides the proper bias voltage to the amplifier. However, this scheme requires the use of a half-supply bypass capacitor to improve the bias voltage's stability and the amplifier's PSRR performance. The LM4910 utilizes an internally generated, buffered bandgap reference voltage as the amplifier's bias voltage. This bandgap reference voltage is not a direct function of VDD and therefore is less susceptible to noise or ripple on the power supply line. This allows for the LM4910 to have a stable bias voltage and excellent PSRR performance even without a half-supply bypass capacitor. 10 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 OUTPUT TRANSIENT ('CLICK AND POPS') ELIMINATED The LM4910 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. The LM4910 remains in a muted condition until there is sufficient input signal magnitude (>5mVRMS, typ) to mask any remaining transient that may occur. Figure 2 shows the LM4910's lack of transients in the differential signal (Trace B) across a 320 load. The LM4910's active-low SHUTDOWN pin is driven by the logic signal shown in Trace A. Trace C is the VO1 output signal and Trace D is the VO3 output signal. To ensure optimal click and pop performance under low gain configurations (less than 0dB), it is critical to minimize the RC combination of the feedback resistor RF and stray input capacitance at the amplifier inputs. A more reliable way to lower gain or reduce power delivered to the load is to place a current limiting resistor in series with the load as explained in the Minimizing Output Noise / Reducing Output Power section. AMPLIFIER CONFIGURATION EXPLANATION As shown in Figure 1, the LM4910 has three operational amplifiers internally. Two of the amplifier's have externally configurable gain while the other amplifier is internally fixed at the bias point acting as a unity-gain buffer. The closed-loop gain of the two configurable amplifiers is set by selecting the ratio of Rf to Ri. Consequently, the gain for each channel of the IC is AV = -(Rf/Ri) (1) By driving the loads through outputs VO1 and VO2 with VO3 acting as a buffered bias voltage the LM4910 does not require output coupling capacitors. The typical single-ended amplifier configuration where one side of the load is connected to ground requires large, expensive output coupling capacitors. A configuration such as the one used in the LM4910 has a major advantage over single supply, single-ended amplifiers. Since the outputs VO1, VO2, and VO3 are all biased at VREF = 1.58V, no net DC voltage exists across each load. This eliminates the need for output coupling capacitors that are required in a single-supply, singleended amplifier configuration. Without output coupling capacitors in a typical single-supply, single-ended amplifier, the bias voltage is placed across the load resulting in both increased internal IC power dissipation and possible loudspeaker damage. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4(VDD) 2 / (π2RL) (2) It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. Since the typical application is for headphone operation (32Ω impedance) using a 3.3V supply the maximum power dissipation is only 138mW. Therefore, power dissipation is not a major concern. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 11 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com POWER SUPPLY BYPASSING As with any amplifier, proper supply bypassing is important for low noise performance and high power supply rejection. The capacitor location on the power supply pins should be as close to the device as possible. Typical applications employ a 3.3V regulator with 10µF tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the LM4910. A bypass capacitor value in the range of 0.1µF to 1µF is recommended for CS. MICRO POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4910's shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN pin. When active, the LM4910's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The trigger point is 0.4V(max) for a logic-low level, and 1.5V(min) for a logic-high level. The low 0.1µA(typ) shutdown current is achieved by applying a voltage that is as near as ground as possible to the SHUTDOWN pin. A voltage that is higher than ground may increase the shutdown current. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 100kΩ pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the SHUTDOWN pin to ground, activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull-up resistor. SELECTING EXTERNAL COMPONENTS Selecting proper external components in applications using integrated power amplifiers is critical to optimize device and system performance. While the LM4910 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4910 is unity-gain stable which gives the designer maximum system flexibility. The LM4910 should be used in low gain configurations to minimize THD+N values, and maximize the signal to noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1Vrms are available from sources such as audio codecs. Very large values should not be used for the gain-setting resistors. Values for Ri and Rf should be less than 1MΩ. Please refer to the section, Audio Power Amplifier Design, for a more complete explanation of proper gain selection Besides gain, one of the major considerations is the closed-loop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Ci, forms a first order high pass filter which limits low frequency response. This value should be chosen based on needed frequency response and turn-on time. SELECTION OF INPUT CAPACITOR SIZE Amplifiying the lowest audio frequencies requires a high value input coupling capacitor, Ci. A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the headphones used in portable systems have little ability to reproduce signals below 60Hz. Applications using headphones with this limited frequency response reap little improvement by using a high value input capacitor. In addition to system cost and size, turn-on time is affected by the size of the input coupling capacitor Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage. This charge comes from the output via the feedback Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on time can be minimized. A small value of Ci (in the range of 0.1µF to 0.39µF), is recommended. 12 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 USING EXTERNAL POWERED SPEAKERS The LM4910 is designed specifically for headphone operation. Often the headphone output of a device will be used to drive external powered speakers. The LM4910 has a differential output to eliminate the output coupling capacitors. The result is a headphone jack sleeve that is connected to VO3 instead of GND. For powered speakers that are designed to have single-ended signals at the input, the click and pop circuitry will not be able to eliminate the turn-on/turn-off click and pop. Unless the inputs to the powered speakers are fully differential the turn-on/turn-off click and pop will be very large. AUDIO POWER AMPLIFIER DESIGN A 30mW/32Ω Audio Amplifier Given: Power Output 30mWrms Load Impedance 32Ω Input Level 1Vrms Input Impedance 20kΩ A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be easily found. Since 3.3V is a standard supply voltage in most applications, it is chosen for the supply rail in this example. Extra supply voltage creates headroom that allows the LM4910 to reproduce peaks in excess of 30mW without producing audible distortion. At this time, the designer must make sure that the power supply choice along with the output impedance does no violate the conditions explained in the Power Dissipation section. Once the power dissipation equations have been addressed, the required differential gain can be determined from Equation 2. (3) From Equation 2, the minimum AV is 0.98; use AV = 1. Since the desired input impedance is 20kΩ, and with AV equal to 1, a ratio of 1:1 results from Equation 1 for Rf to Ri. The values are chosen with Ri = 20kΩ and Rf = 20kΩ. The last step in this design example is setting the amplifier's −3dB frequency bandwidth. To achieve the desired ±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth limit. The gain variation for both response limits is 0.17dB, well within the ±0.25dB desired limit. The results are an fL = 100Hz/5 = 20Hz (4) and an fH = 20kHz x 5 = 100kHz (5) As mentioned in the Selecting Proper External Components section, Ri and Ci create a highpass filter that sets the amplifier's lower bandpass frequency limit. Find the coupling capacitor's value using Equation (3). Ci≥ 1/(2πR ifL) (6) The result is Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 13 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com 1/(2π*20kΩ*20Hz) = 0.397µF (7) Use a 0.39µF capacitor, the closest standard value. The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain, AV. With an AV = 1 and fH = 100kHz, the resulting GBWP = 100kHz which is much smaller than the LM4910 GBWP of 11MHz. This figure displays that if a designer has a need to design an amplifier with higher differential gain, the LM4910 can still be used without running into bandwidth limitations. MINIMIZING OUTPUT NOISE / REDUCING OUTPUT POWER Figure 6. Output noise delivered to the load can be minimized with the use of an external resistor, RSERIES, placed in series with each load as shown in Figure 6. RSERIES forms a voltage divider with the impedance of the headphone driver RL. As a result, output noise is attenuated by the factor RL / (RL + RSERIES). Figure 7 illustrates the relationship between output noise and RSERIES for different loads. RSERIES also decreases output power delivered to the load by the factor RL / (RL + RSERIES)2. However, this may not pose a problem since most headphone applications require less than 10mW of output power. Figure 9 illustrates output power (@1% THD+N) vs RSERIES for different loads. Figure 7 shows an optional resistor connected between the amplifier output that drives the headphone jack sleeve and ground. This resistor provides a ground path that supressed power supply hum. This hum may occur in applications such as notebook computers in a shutdown condition and connected to an external powered speaker. The resistor's 100Ω value is a suggested starting point. Its final value must be determined based on the tradeoff between the amount of noise suppression that may be needed and minimizing the additional current drawn by the resistor (25mA for a 100Ω resistor and a 5V supply). ESD PROTECTION As stated in the Absolute Maximum Ratings, pin 6 (Vo3) on the LM4910 has a maximum ESD susceptibility rating of 10kV. For higher ESD voltages, the addition of a PCDN042 dual transil (from California Micro Devices), as shown in Figure 7, will provide additional protection. 14 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Figure 7. The PCDN042 provides additional ESD protection beyond the 10kV shown in the Absolute Maximum Ratings for the Vo3 output Figure 8. Output Noise vs RSERIES Figure 9. Figure 10. Output Power vs RSERIES Figure 11. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 15 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com HIGHER GAIN AUDIO AMPLIFIER The LM4910 is unity-gain stable and requires no external components besides gain-setting resistors, input coupling capacitors, and proper supply bypassing in the typical application. However, if a very large closed-loop differential gain is required, a feedback capacitor (Cf) may be needed as shown in Figure 11 to bandwidth limit the amplifier. This feedback capacitor creates a low pass filter that eliminates possible high frequency oscillations. Care should be taken when calculating the -3dB frequency in that an incorrect combination of Rf and Cf will cause frequency response roll off before 20kHz. A typical combination of feedback resistor and capacitor that will not produce audio band high frequency roll off is Rf = 20kΩ and Cf = 25pF. These components result in a -3dB point of approximately 320kHz. REFERENCE DESIGN BOARD and LAYOUT GUIDELINES MSOP & SO BOARDS (Note: RPU2 is not required. It is used for test measurement purposes only.) 16 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 LM4910 SO DEMO BOARD ARTWORK Figure 12. Composite View Figure 13. Silk Screen Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 17 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Figure 14. Top Layer Figure 15. Bottom Layer 18 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 LM4910 MSOP DEMO BOARD ARTWORK Figure 16. Composite View Figure 17. Silk Screen Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 19 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Figure 18. Top Layer Figure 19. Bottom Layer 20 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 LM4910 LLP DEMO BOARD ARTWORK Figure 20. Composite View Figure 21. Silk Screen Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 21 LM4910 SNAS151G – MAY 2004 – REVISED MARCH 2007 www.ti.com Figure 22. Top Layer Figure 23. Bottom Layer LM4910 Reference Design Boards Bill of Materials Part Description Qty LM4910 Mono Reference Design Board 1 Ref Designator LM4910 Audio AMP 1 U1 Tantalum Cap 1µF 16V 10 1 Cs Ceramic Cap 0.39µF 50V Z50 20 2 Ci Resistor 20kΩ 1/10W 5 4 Ri, Rf Resistor 100kΩ 1/10W 5 1 Rpu Jumper Header Vertical Mount 2X1, 0.100 1 J1 PCB LAYOUT GUIDELINES This section provides practical guidelines for mixed signal PCB layout that involves various digital/analog power and ground traces. Designers should note that these are only "rule-of-thumb" recommendations and the actual results will depend heavily on the final layout. 22 Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 LM4910 www.ti.com SNAS151G – MAY 2004 – REVISED MARCH 2007 Minimization of THD PCB trace impedance on the power, ground, and all output traces should be minimized to achieve optimal THD performance. Therefore, use PCB traces that are as wide as possible for these connections. As the gain of the amplifier is increased, the trace impedance will have an ever increasing adverse affect on THD performance. At unity-gain (0dB) the parasitic trace impedance effect on THD performance is reduced but still a negative factor in the THD performance of the LM4910 in a given application. GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION Power and Ground Circuits For two layer mixed signal design, it is important to isolate the digital power and ground trace paths from the analog power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central point rather than daisy chaining traces together in a serial manner) can greatly enhance low level signal performance. Star trace routing refers to using individual traces to feed power and ground to each circuit or even device. This technique will require a greater amount of design time but will not increase the final price of the board. The only extra parts required may be some jumpers. Single-Point Power / Ground Connections The analog power traces should be connected to the digital traces through a single point (link). A "PI-filter" can be helpful in minimizing high frequency noise coupling between the analog and digital sections. Further, place digital and analog power traces over the corresponding digital and analog ground traces to minimize noise coupling. Placement of Digital and Analog Components All digital components and high-speed digital signal traces should be located as far away as possible from analog components and circuit traces. Avoiding Typical Design / Layout Problems Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB layer. When traces must cross over each other do it at 90 degrees. Running digital and analog traces at 90 degrees to each other from the top to the bottom side as much as possible will minimize capacitive noise coupling and cross talk. Revision History Rev Date Description 1.0 7/12/05 Released to the WEB. 1.1 01/16/07 Deleted the phrase “patent pending” on page 1. Submit Documentation Feedback Copyright © 2004–2007, Texas Instruments Incorporated Product Folder Links: LM4910 23 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) LM4910LQ/NOPB ACTIVE WQFN NGP 8 1000 RoHS & Green SN Level-3-260C-168 HR -40 to 85 GA4 LM4910MM/NOPB ACTIVE VSSOP DGK 8 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 GC2 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of