CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE GENERAL DESCRIPTION FEATURES The CM8662 is a bridge-connected audio power amplifier No output coupling capacitors, bootstrap capacitors or capable of delivering typically 675mW of continuous average snubber circuits are necessary. power to an 8Ω load with 1% (THD) from a 5V power supply. SOP, SOP with Power Pad or DIP package. Boomer audio power amplifiers were designed specifically to Unity-gain stable provide high quality output power with a minimal amount of External gain configuration capability external components. Since the CM8662 does not require output coupling capacitors, bootstrap capacitors, or snuuber networks, it is optimally suited for low-power portable systems. KEY SPECIFICATION The CM8662 features an externally controlled, low-power THD at 500mW continuous average output power at consumption shutdown mode, as well as an internal thermal 1kHz into 8Ω shutdown protection mechanism. Output power at 10% THD+N at 1kHz into 8Ω 1% (max) 825mW (typ) The unity-gain stable CM8662 can be configured by external Shutdown Current 0.7μA (typ) gain-setting resistors. APPLICATIONS PIN CONFIGURATION PDIP/SOP/PSOP (Top View) Portable Computers Cellular Phones Toys and Games 2003/04/30 Rev. 1.1 1 SHUTDOW N Vo2 8 2 BYPASS GND 7 3 +IN VDD 6 4 -IN Vo1 5 Champion Microelectronic Corporation Page 1 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE APPLICATION CIRCUIT VDD Cs 0.1uF Rf 20kΩ 6 4 Ri 20k Ω *Ci 3 -IN +IN - Vo1 5 + 10kΩ Audio Input 50kΩ RL 8Ω 10kΩ 2 VDD Bypass VDD/2 Vo2 8 + Av = -1 CB 0.1uF 50kΩ RPU 1 Shutdown Bias NC 7 ORDERING INFORMATION Part Number Temperature Range Package CM8662IP -40℃ ~ +85℃ 8-PIN PDIP (P08) CM8662IS -40℃ ~ +85℃ 8-PIN SOP (S08) CM8662PIS -40℃ ~ +85℃ 8-PIN PSOP (PS08) 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 2 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE ABSOLUTE MAXIMUM RATINGS (Note 2) Thermal Resistance Supply Voltage (VIN) ………………………….……………. +6.0V Storage Temperature (TS) ……….……………. -65℃ to +150℃ Input Voltage (VIN) ………………………… -0.3V to VDD + 0.3V Power Dissipation (Note 3) …………………… Internally Limited ESD Susceptibility (Note 4) ……………………………….. 3500V ESD Susceptibility (Note 5) ………………………………... 250V Junction Temperature ……………………………………… 150℃ Soldering Information ΘJc (typ) – SOP-08……..…………………………….. 35℃/W ΘJc (typ) – PDIP-08………………………………….. 37℃/W ΘJC (typ) – PSOP-08…………………………………. 14℃/W OPERATING RATINGS (Note 2) Temperature Range TMIN≦TA≦TMAX …………………………. -40℃≦TA≦+85℃ Supply Voltage (VIN) …….……..…………2.7V≦VDD≦5.5V Small Outline Package Vapor Phase (60 sec) ……………………………….….. 215℃ Infrared (15 sec) …………………………………………. 220℃ ELECTRICAL CHARACTERISTICS (Note 1) (Note 2) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25℃. Symbol Parameter Test Conditions CM8662 Min. Typ. Unit VDD Supply Voltage 5.5 V IDD Quiescent Power Supply VIN = 0V, IO = 0A (Note 8) 3.6 6.5 mA ISD Shutdown Current VPIN1 = VDD 0.7 5 μA VOS Output offset Voltage VIN = 0V 5 50 mV THD = 1% (max); f = 1kHz; RL = 8Ω 675 PO THD + N PSRR Output Power 2.7 Max. THD+N = 10% ; f = 1kHz; RL = 8Ω Total Harmonic Distortion + PO = 500mWrms; RL = 8Ω Noise AVD = 2; 20Hz≦f≦20kHz Power Supply Rejection Ratio VDD = 4.9V to 5.1V 500 mW 825 0.55 % 50 dB Note 1. All voltage 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 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 temperature and is dictated by TJMAX, ΘJA and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TMAX - TA)/ ΘJA . The typical junction-to-ambient thermal resistance, when board mounted, is 170℃/W for package SOP-08, and PSOP-08, and is 107℃/W for package number PDIP-08 Note 4. Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5. Machine model, 200 pF - 240 pF discharged through all pins. 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 3 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE AUTOMATIC SWITCHING CIRCUIT VDD 20kΩ 0.1uF Control Pin 8 2 + CM8608 0.33uF 20k Ω Audio Input 3 1 + Ro 1 kΩ 4 + 1uF Rp 1 MΩ VDD 20k Ω To CM8662 Channel B Output (Pin 7) via Coupling Capacitor 0.1uF + 0.33uF 4 20k Ω 1uF Headphone Jack 100uF 3 6 CM8662 + 7 1 2 RL 8Ω 5 8 + EXTERNAL COMPONENTS DESCRIPTION (Figure 1) Components Functional Description 1 Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also 2 Ci Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a forms a high pass filter with Ci and fc = 1/(2πRiCi) highpass 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 proper placement and selection of the supply bypass capacitor. 5 CB Bypass pin capacitor which provides half-supply filtering. Refer to the Proper Selection of External Components section for proper placement and selection of the half-supply bypass capacitor. 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 4 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE APPLICATION INFORMATION Bridge Configuration Explanation As shown in Figure 1, the CM8662 has two operational amplifiers internally, allowing for a few different amplifier configuration. The first amplifier's gain is externally configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier's gain is fixed by the two internal 10kΩ resistors. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase 180°. Consequently, the differential gain for the IC is AVD = 2*(Rf/Ri) By dividing the load differentially through output Vo1 and Vo2, and amplifier configuration commonly referred to as "bridged mode" is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Consequently, four times the output power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier's closed-loop gain without causing excessive clipping which will damage high frequency transducers used in loudspeaker systems, please refer to the Audio Power Amplifier Design section. A bridge configuration, such as the one used in CM8662, also creates a second advantage over single-ended amplifier. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal IC power dissipation and also permanent loudspeaker damage. Power Dissipation Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Equation 1 states the maximum power dissipation point for a bridge amplifier operating at a given supply voltage and driving a specified output load. 2 2 (1) PDMAX = 4*(VDD) /(2π RL) Since the CM8662 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. Even with this substantial increase in power dissipation, the CM8662 does not require heatsinking. From Equation 1, assuming a 5V power supply and an 8Ω load, the maximum power dissipation point is 625mW. The maximum power dissipation point obtained from Equation 1 must not be greater than the power dissipation that results from Equation 2: (2) PDMAX = (TJMAX-TA)/ΘJA 2003/04/30 Rev. 1.1 For package M08A, ΘJA= 170℃/W and for package N08E, Θ 107℃/W. TJMAX=150℃ for the CM8662. Depending on the ambient temperature, TA, of the system surroundings, Equation 2 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 is greater than that of Equation 2, then wither the supply voltage must be decreased, the load impedance increased, or the ambient temperature reduced. For the typical application of a 5V power supply, with an 8Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 44℃ provided that device operation is around the maximum power dissipation point. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature can be increased. Refer to the Typical Performance Characteristics curves for power dissipation information for lower output powers. JA= Power Supply Bypassing As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitor location on both the bypass and power supply pins should be as close to the device as possible. As displayed in the Typical Performance Characteristics section, the effect of a larger half supply bypass capacitor is improved PSSR due to increased half-supply stability. Typical applications employ a 5V regulator with 10μF and a 0.1μF bypass capacitors which aid in supply stability, but do not eliminate the need for bypassing the supply nodes of the CM8662. The selection of bypass capacitors, especially CB, is thus dependant upon desired PSSR requirements, click and pop performance as explained in the section, Proper Selection of External Components, system cost, and size constraints. Shutdown Function In order to reduce power consumption while not in use, the CM8662 contains a shutdown pin to externally turn off the amplifier's bias circuitry. The shutdown feature turns the amplifier off when a logic high is placed on the shutdown pin. The trigger point between a logic low and logic high level is typically half supply. It is best to switch between ground and supply to provide maximum device performance. By switching the shutdown pin to VDD, the CM8662 supply current draw will be minimized in idle mode. While the device will be disabled with shutdown pin voltage less than VDD, the idle current may be greater than the typical value of 0.7μA. In either case, the shutdown pin should be tied to a definite voltage because leaving the pin floating may result in an unwanted shutdown condition. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry which provides a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch that when closed, is connected to ground and enables the amplifier. If the switch is open, then a soft pull-up resistor of 47 kΩ will disable the CM8662. There are no soft pull-up resistors inside the CM8662, so a definite shutdown pin voltage must be applied externally, or the internal logic gate will be left floating which could disable the amplifier unexpectedly. Champion Microelectronic Corporation Page 5 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE APPLICATION INFORMATION (CONTINUED) Proper Selection of External Components Proper selection of external components in applications using integrated power amplifiers is critical to optimize device and system performance. While the CM8662 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The CM8662 is unity-gain stable which gives a designer maximum system flexibility. The CM8662 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. 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 band-width is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Cj, forms a first order high pass filter which limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons. Selection of Input Capacitor Size Large input capacitors are both expensive and space hungry for portable design. Clearly, a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 100-150Hz. Thus using a large input capacitors may not increase system performance. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Cj. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable. Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized. Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the CM8662 turns on. The slower the CM8662's, outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 1.0μF along with a small value of Cj (in the range of 0.1μF to 0.39μF), should produce virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1μF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 0.1μF or larger is recommended in all but the most cost sensitive designs. Audio Power Amplifier Design Design a 500mW/8Ω Audio Amplifier Given: Power Output 500mWrms Load Impedance 8Ω Input Level 1 Vrms Input Impedance 20kΩ Bandwidth 100Hz-20kHz±0.25dB 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. A second way to determine the minimum supply rail is to calculate the required Vopeak using equation 3 and add the dropout voltage. Using this method, the minimum supply voltage would be (Vopeak + (2*VOD)), where VOD is extrapolated from the Dropout Voltage vs Supply Voltage curve in the Typical Performance Characteristics section. Vopeak = (2RLP0) (3) Using the Output Power vs Supply Voltage graph for an 8Ω load, the minimum supply rail is 4.3V. But since 5V is a standard supply voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the CM8662 to reproduce peaks in excess of 500mW without clipping the signal. At this time, the designer must make sure that the power supply choice along with the output impedance does not 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 4. AVD≧ (RLP0) /(VIN) = Vorms/Vinrms Ri/Rf=AVD/2 (5) (4) For Equation 4, the minimum AVD is 2; use AVD=2. Since the desired input impedance was 20kΩ, and with a AVD of 2, a ratio of 1:1 of Rf to Ri results in an allocation of Ri=Rf= 20kΩ. The final design step is to address the bandwidth requirements which must be stated as a pair of -3dB frequency points. Five times away from a -3dB point is 0.17dB down from passband response which is better than the required ±0.25dB specified. This fact results in a low and high frequency pole of 20Hz and 100kHz respectively. As stated in the External Components section, Rj in conjunction with Cj create a highpass filter. Cj≧1/(2π*20 kΩ*20Hz)=0.397μF; use 0.39μF The high frequency pole is determined by the product of the desired high frequency pole, fH, and the differential gain, AVD. With an AVD=2 and fH=100kHz, the resulting GBWP of 12.5MHz. This figure displays that if a designer has a need to design an amplifier with a high differential gain, the CM8662 can still be used without running into bandwidth problems. 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 6 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE PACKAGE DIMENSION 8-PIN PDIP (P08) PIN 1 ID θ θ 8-PIN SOP (S08) PIN 1 ID θ θ 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 7 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE PACKAGE DIMENSION 8-PIN PSOP (PS08) θ θ 2003/04/30 Rev. 1.1 Champion Microelectronic Corporation Page 8 CM8662 AUDIO POWER AMP. WITH SHUTDOWN MODE IMPORTANT NOTICE Champion Microelectronic Corporation (CMC) reserves the right to make changes to its products or to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. A few applications using integrated circuit products may involve potential risks of death, personal injury, or severe property or environmental damage. CMC integrated circuit products are not designed, intended, authorized, or warranted to be suitable for use in life-support applications, devices or systems or other critical applications. Use of CMC products in such applications is understood to be fully at the risk of the customer. In order to minimize risks associated with the customer’s applications, the customer should provide adequate design and operating safeguards. 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