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| CM8662 BOOKLY MICRO GENERAL DESCRIPTION The CM8662 is a bridge-connected audio power amplifier capable of delivering typically 1.7W of continuous average power to an 4 load from a 5V power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of 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. 1.7W CMOS AUDIO AMP FEATURES No output coupling capacitors, bootstrap capacitors or snubber circuits are necessary. SOP, SOP with Power Pad or DIP package. Unity-gain stable External gain configuration capability CMOS technology , save power , Hi-Fi performance higher efficiency than traditional bipolar amplifier KEY SPECIFICATION The CM8662 features an externally controlled, low-power consumption shutdown mode, as well as an internal thermal shutdown protection mechanism. The unity-gain stable CM8662 can be configured by external gain-setting resistors. THD at 0.5W continuous average output power at 1kHz into 8 1W (typ) Shutdown Current 0.7A (typ) 0.5% (max) Output power at 10% THD+N at 1kHz into 8 APPLICATIONS Walkie-talkie LCD-TV / monitor Toys and Games USB speaker Digital recorder PIN CONFIGURATION DIP/SOP (Top View) 1 2 3 4 SHUTDOW N BYPASS +IN -IN Vo2 GND VDD Vo1 8 7 6 5 2004/05/30 www.bookly.com Page 1 CM8662 BOOKLY MICRO Test CIRCUIT VDD 1.7W CMOS AUDIO AMP Cs 0.1uF Rf 20k 6 4 *Ci Ri 20k -IN + 10k 50k 10k - Vo1 5 3 +IN Audio Input RL 8 Vo2 8 2 VDD CB 0.1uF Bypass VDD/2 + Av = -1 50k RPU 1 NC Shutdown Bias 7 ORDERING INFORMATION Part Number CM8662IP CM8662IS Temperature Range -40 ~ +85 -40 ~ +85 Package 8-PIN DIP8 8-PIN SOP8 2004/05/30 www.bookly.com Page 2 CM8662 BOOKLY MICRO ABSOLUTE MAXIMUM RATINGS (Note 2) 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 Small Outline Package Vapor Phase (60 sec) .......................................... 215 Infrared (15 sec) ................................................. 220 Thermal Resistance Jc (typ) - SOP-08........................................... 35/W Jc (typ) -DIP-08......................................... 37/W 1.7W CMOS AUDIO AMP OPERATING RATINGS (Note 2) Temperature Range TMINTATMAX ............................... -40TA+85 Supply Voltage (VIN) ...........................2.7VVDD5.5V ELECTRICAL CHARACTERISTICS (Note 1) (Note 2) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25. CM8662 Min. 2.7 VIN = 0V, IO = 0A (Note 8) VPIN1 = VDD VIN = 0V THD = 1% (max); f = 1kHz; RL = 8 THD+N = 10% ; f = 1kHz; RL = 8 PO = 500mWrms; RL = 8 AVD = 2; 20Hzf20kHz VDD = 4.9V to 5.1V 500 3.6 0.7 5 875 1000 0.55 50 Typ. Max. 5.5 6.5 5 50 Symbol VDD IDD ISD VOS PO THD + N PSRR Parameter Supply Voltage Quiescent Power Supply Shutdown Current Output offset Voltage Output Power Total Harmonic Distortion + Noise Power Supply Rejection Ratio Test Conditions Unit V mA A mV mW % 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, JA and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TMAX - TA)/ JA . 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 1.5k resistor. Note 5. Machine model, 200 pF - 240 pF discharged through all pins. 2004/05/30 www.bookly.com Page 3 CM8662 BOOKLY MICRO AUTOMATIC SWITCHING CIRCUIT 1.7W CMOS AUDIO AMP VDD 20k 0.1uF 8 + 0.33uF 20k Control Pin 100uF Headphone Jack 2 CM8608 3 + 4 1 + Ro 1 k Rp 1 M Audio Input 1uF VDD 20k 0.1uF 6 RL 8 5 To CM8662 Channel B Output (Pin 7) via Coupling Capacitor + 0.33uF 20k 4 CM8662 3 + 71 2 8 1uF + EXTERNAL COMPONENTS DESCRIPTION (Figure 1) Components 1 2 Ri Ci Functional Description Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass filter with Ci and fc = 1/(2RiCi) Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a highpass filter with Ri at fc = 1/(2RiCi). Refer to the section, Proper Selection of External Components, for an explanation of how to determine the value of Ci. 3 4 5 RF CS CB Feedback resistance which sets the closed-loop gain in conjunction with Ri. 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. 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. 2004/05/30 www.bookly.com Page 4 CM8662 BOOKLY MICRO 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 10k 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) /(2 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 8 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)/JA For package M08A, JA= 170/W and for package N08E, 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 8 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= 1.7W CMOS AUDIO AMP 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 10F and a 0.1F 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 0.7A. 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 k 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. 2004/05/30 www.bookly.com Page 5 CM8662 BOOKLY MICRO 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 1.0F along with a small value of Cj (in the range of 0.1F to 0.39F), should produce virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1F, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 0.1F or larger is recommended in all but the most cost sensitive designs. Audio Power Amplifier Design Design a 500mW/8 Audio Amplifier Given: Power Output 500mWrms Load Impedance 8 Input Level 1 Vrms Input Impedance 20k Bandwidth 100Hz-20kHz0.25dB 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 = 1.7W CMOS AUDIO AMP (2RLP0) (3) Using the Output Power vs Supply Voltage graph for an 8 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 (5) Ri/Rf=AVD/2 (4) For Equation 4, the minimum AVD is 2; use AVD=2. Since the desired input impedance was 20k, and with a AVD of 2, a ratio of 1:1 of Rf to Ri results in an allocation of Ri=Rf= 20k. 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. Cj1/(2*20 k*20Hz)=0.397F; use 0.39F 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. 2004/05/30 www.bookly.com Page 6 CM8662 BOOKLY MICRO Application circuit : 1.7W CMOS AUDIO AMP CM8662 22K Audio_in 4 3 2 1 47K CM8662 105 -IN +IN BYPASS SHDN VDD VO1 VO2 5 8 R1 2.2K on/off 1=off 105 104 6 GND 7 R2 +5V 22uF 10ohm www.bookly.com R1,R2,PSRR , R1,R2 47K 47K 2004/05/30 www.bookly.com Page 7 CM8662 BOOKLY MICRO PACKAGE DIMENSION 8-PIN DIP8 1.7W CMOS AUDIO AMP PIN 1 ID 8-PIN SOP8 PIN 1 ID 2004/05/30 www.bookly.com Page 8 |
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