a FEATURES 1.5 Watt Output1 Differential (BTL2)Output Single-Supply Operation: 2.7 V to 5.5 V Functions Down to 1.75 V Wide Bandwidth: 4 MHz Highly Stable, Phase Margin: > 80 Degrees Low Distortion: 0.2% THD @ 1 W Output Excellent Power Supply Rejection APPLICATIONS Portable Computers Personal Wireless Communicators Hands-Free Telephones Speakerphones Intercoms Musical Toys and Speaking Games Low Distortion 1.5 Watt Audio Power Amplifier SSM2211* FUNCTIONAL BLOCK DIAGRAM V+ IN – VOUT A IN + VOUT B BYPASS SHUTDOWN BIAS V – (GND) GENERAL DESCRIPTION The SSM2211 is a high performance audio amplifier that delivers 1 W RMS of low distortion audio power into a bridge-connected 8 Ω speaker load, (or 1.5 W RMS into 4 Ω load). It operates over a wide temperature range and is specified for single-supply voltages between 2.7 V and 5.5 V. When operating from batteries, it will continue to operate down to 1.75 V. This makes the SSM2211 the best choice for unregulated applications such as toys and games. Featuring a 4 MHz bandwidth, distortion below 0.2 % THD @ 1 W, and the patented Thermal Coastline leadframe, superior performance is delivered at higher power or lower speaker load impedance than competitive units. The advanced mechanical packaging of the SSM2211 gives lower chip temperature, which ensures highly reliable operation and enhanced trouble free life. The low differential dc output voltage results in negligible losses in the speaker winding, and makes high value dc blocking capacitors unnecessary. Battery life is extended by using the Shutdown mode, which reduces quiescent current drain to typically 100 nA. The SSM2211 is designed to operate over the –20°C to +85°C temperature range. See Figure 49 for information on the Thermal Coastline lead frame. The SSM2211 is available in an SO-8 surface mount package. DIP samples are available; you should request a special quotation on production quantities. An evaluation board is available upon request of your local Analog Device sales office. Applications include personal portable computers, hands-free telephones and transceivers, talking toys, intercom systems and other low voltage audio systems requiring 1 W output power. *Protected by U.S. Patent No. 5,519,576 1 1.5 W @ 4 Ω, +25°C ambient, < 1% THD, 5 V supply, 4 layer PCB. 2Bridge Tied Load REV. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1997 SSM2211–SPECIFICATIONS ELECTRICAL CHARACTERISTICS (V = 15.0 V, T = 1258C, R = 8 V, C S A L B = 0.1 mF, VCM = VD/2 unless otherwise noted) Parameter Symbol Conditions Min GENERAL CHARACTERISTICS Differential Output Offset Voltage Output Impedence VOOS ZOUT AVD = 2 SHUTDOWN CONTROL Input Voltage High Input Voltage Low VIH VIL ISY = < 100 µA ISY = Normal POWER SUPPLY Power Supply Rejection Ratio Supply Current Supply Current, Shutdown Mode PSRR ISY ISD VS = 4.75 V to 5.25 V VO1 = VO2 = 2.5 V Pin 1 = VDD, See Figure 29 DYNAMIC PERFORMANCE Gain Bandwidth Phase Margin GBP Ø0 AUDIO PERFORMANCE Total Harmonic Distortion Total Harmonic Distortion Voltage Noise Density THD + N THD + N en S A L Max Units 4 0.1 50 mV Ω 3.0 1.3 P = 0.5 W into 8 Ω, f = 1 kHz P = 1.0 W into 8 Ω, f = 1 kHz f = 1 kHz ELECTRICAL CHARACTERISTICS (V = 13.3 V, T = 1258C, R = 8 V, C Typ B V V 66 9.5 100 dB mA nA 4 86 MHz degrees 0.15 0.2 85 % % nV√Hz = 0.1mF, VCM = VD/2 unless otherwise noted) Parameter Symbol Conditions Min Typ Max Units GENERAL CHARACTERISTICS Differential Output Offset Voltage Output Impedence VOOS ZOUT AVD = 2 5 0.1 50 mV Ω SHUTDOWN INPUT Input Voltage High Input Voltage Low VIH VIL ISY = < 100 µA POWER SUPPLY Supply Current Supply Current, Shutdown Mode ISY ISD VO1 = VO2 = 1.65 V Pin 1 = VDD, See Figure 29 5.2 100 mA nA AUDIO PERFORMANCE Total Harmonic Distortion THD + N P = 0.35 W into 8 Ω, f = 1 kHz 0.1 % 1.7 1 ELECTRICAL CHARACTERISTICS (V = 12.7 V, T = 1258C, R = 8 V, C S A L B V V = 0.1 mF, VCM = VS/2 unless otherwise noted) Parameter Symbol Conditions Min Typ Max Units GENERAL CHARACTERISTICS Differential Output Offset Voltage Output Impedence VOOS ZOUT AVD = 2 5 0.1 50 mV Ω SHUTDOWN CONTROL Input Voltage High Input Voltage Low VIH VIL ISY = < 100 µA ISY = Normal POWER SUPPLY Supply Current Supply Current, Shutdown Mode ISY ISD VO1 = VO2 = 1.35 V Pin 1 = VDD, See Figure 29 4.2 100 mA nA AUDIO PERFORMANCE Total Harmonic Distortion THD + N P = 0.25 W into 8 Ω, f = 1 kHz 0.1 % 1.5 0.8 V V Specifications subject to change without notic –2– REV. 0 SSM2211 ABSOLUTE MAXIMUM RATINGS 1,2 ORDERING GUIDE Supply Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +6 V Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VDD Common Mode Input Voltage . . . . . . . . . . . . . . . . . . . . . . VDD ESD Susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000 V Storage Temperature Range . . . . . . . . . . . . 265°C to +150°C Operating Temperature Range . . . . . . . . . . . 220°C to +85°C Junction Temperature Range . . . . . . . . . . . . 265°C to +165°C Lead Temperature Range (Soldering, 60 sec) . . . . . . . 1300°C Model Temperature Range Package Description Package Options SSM2211S SSM2211S-reel SSM2211S-reel7 SSM2211P –20°C to +85°C –20°C to +85°C –20°C to +85°C –20°C to +85°C 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead PDIP SO-8 SO-8 SO-8 N-8* * NOTES 1 Absolute maximum ratings apply at +25°C, unless otherwise noted. 2 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Special order only. PIN CONFIGURATIONS 8-Lead SOIC (SO-8) 8 VOUT B SHUTDOWN 1 Package Type uJA1 uJC Units 8-Lead SOIC (S) 8-Lead PDIP (P)2 98 103 43 43 °C/W °C/W 7 –V TOP VIEW +IN 3 (Not to Scale) 6 +V BYPASS 2 5 VOUT A –IN 4 NOTES 1 For the SOIC package, θJA is measured with the device soldered to a 4-layer printed circuit board. 2 Special order only. 8-Lead Plastic DIP (N-8) 8 VOUT B SHUTDOWN 1 7 –V TOP VIEW +IN 3 (Not to Scale) 6 +V BYPASS 2 5 VOUT A –IN 4 CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the SSM2211 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. 0.01 20 CB = 0 CB = 0.1mF CB = 0 10k 20k Figure 1. THD+N vs. Frequency REV. 0 1 CB = 1mF 0.1 1k FREQUENCY – Hz CB = 0.1mF 1 CB = 1mF 100 10 10 CB = 0.1mF 0.1 ESD SENSITIVE DEVICE THD + N – % THD + N – % 1 TA = 1258C VDD = 5V AVD = 2 (BTL) RL = 8V PL = 500mW THD + N – % 10 WARNING! 0.01 20 0.1 TA = 1258C VDD = 5V AVD = 10 (BTL) RL = 8V PL = 500mW 100 1k FREQUENCY – Hz 10k 20k Figure 2. THD+N vs. Frequency –3– CB = 1mF 0.01 20 TA = 1258C VDD = 5V AVD = 20 (BTL) RL = 8V PL = 500mW 100 1k FREQUENCY – Hz 10k 20k Figure 3. THD+N vs. Frequency SSM2211–Typical Performance Characteristics 10 CB = 0.1mF 0.1 1k FREQUENCY – Hz 10k 20k 100 1k FREQUENCY – Hz 0.01 20 10k 20k Figure 5. THD+N vs. Frequency 10 THD + N – % 0.1 1 Figure 7. THD+N vs. POUTPUT 0.1 POUTPUT – W 1 Figure 8. THD+N vs. POUTPUT CB = 0 1 CB = 0.1mF 0.1 0.1 100 2 10 1k FREQUENCY – Hz 10k 20k Figure 10. THD+N vs. Frequency 0.01 20 CB = 0.1mF CB = 0.1mF CB = 1mF 100 1 TA = 1258C VDD = 3.3V AVD = 10 (BTL) RL = 8V PL = 350mW CB = 1mF 0.01 20 1 Figure 9. THD+N vs. POUTPUT 1k FREQUENCY – Hz 10k 20k Figure 11. THD+N vs. Frequency –4– THD + N – % THD + N – % 1 0.1 POUTPUT – W CB = 0 THD + N – % TA = 1258C VDD = 3.3V AVD = 2 (BTL) RL = 8V PL = 350mW 10k 20k TA = 1258C VDD = 5V AVD = 2 (BTL) RL = 8V FREQUENCY = 20kHz 1 CB = 0.1mF 0.01 20n 2 10 10 1k FREQUENCY – Hz 0.1 0.01 20n 2 100 10 TA = 1258C VDD = 5V AVD = 2 (BTL) RL = 8V FREQUENCY = 1kHz 1 CB = 0.1mF 0.1 0.1 POUTPUT – W TA = 1258C VDD = 5V AVD = 20 (BTL) RL = 8V PL = 1W Figure 6. THD+N vs. Frequency 10 TA = 1258C VDD = 5V AVD = 2 (BTL) RL = 8V FREQUENCY = 20Hz 1 CB = 0.1mF 0.01 20n CB = 1mF 0.1 TA = 1258C VDD = 5V AVD = 10 (BTL) RL = 8V PL = 1W 0.01 20 Figure 4. THD+N vs. Frequency THD + N – % 1 CB = 1mF 0.1 CB = 1mF 100 CB = 0.1mF 1 THD + N – % CB = 0 CB = 0.1mF 0.01 20 10 CB = 0 THD + N –% THD + N – % 1 TA = 1258C VDD = 5V AVD = 2 (BTL) RL = 8V PL = 1W THD + N – % 10 CB = 1mF 0.1 0.01 20 TA = 1258C VDD = 3.3V AVD = 20 (BTL) RL = 8V PL = 350mW 100 1k FREQUENCY – Hz 10k 20k Figure 12. THD+N vs. Frequency REV. 0 SSM2211 10 0.1 0.1 0.1 POUTPUT – W 1 Figure 13. THD+N vs. POUTPUT TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V PL = 250mW THD + N – % 1 0.1 POUTPUT – W 2 Figure 15. THD+N vs. Frequency CB = 0.1mF CB = 0 CB = 0.1mF 1 10k 20k 1k FREQUENCY – Hz Figure 16. THD+N vs. Frequency 1 CB = 1mF 0.01 20 TA = 1258C VDD = 2.7V AVD = 10 (BTL) RL = 8V PL = 250mW 100 1k FREQUENCY – Hz 10k 20k Figure 17. THD+N vs. Frequency 10 TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V FREQUENCY = 20Hz 1 CB = 1mF 0.1 CB = 1mF 0.01 20 10 TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V FREQUENCY = 1kHz Figure 19. THD+N vs. POUTPUT 2 1k FREQUENCY – Hz 10k 20k TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V FREQUENCY = 20kHz THD + N –% THD + N –% THD + N –% 1 100 1 0.1 0.1 POUTPUT – W TA = 1258C VDD = 2.7V AVD = 20 (BTL) RL = 8V PL = 250mW Figure 18. THD+N vs. Frequency 1 0.1 REV. 0 1 10 0.1 0.01 20n 0.1 POUTPUT – W CB = 0 0.1 100 0.01 20n 2 10 CB = 0.1mF 0.01 20 1 Figure 14. THD+N vs. POUTPUT THD + N – % 10 0.1 0.01 20n 2 TA = 1258C VDD = 3.3V AVD = 2 (BTL) RL = 8V FREQUENCY = 20kHz 1 CB = 0.1mF THD + N – % 0.01 20n 10 10 TA = 1258C VDD = 3.3V AVD = 2 (BTL) RL = 8V FREQUENCY = 1kHz 1 CB = 0.1mF THD + N –% TA = 1258C VDD = 3.3V AVD = 2 (BTL) RL = 8V FREQUENCY = 20Hz 1 CB = 0.1mF THD + N –% THD + N –% 10 0.01 20n 0.1 0.1 POUTPUT – W 1 Figure 20. THD+N vs. POUTPUT –5– 2 0.01 20n 0.1 POUTPUT – W 1 Figure 21. THD+N vs. POUTPUT 2 SSM2211–Typical Performance Characteristics 10 TA = 1258C VDD = 5V AVD = 10 SINGLE ENDED CB = 0.1mF CC = 1000mF 1 THD + N – % THD + N – % 1 RL = 8V PO = 250mW 0.1 100 RL = 32V PO = 20mW 0.01 20 10k 20k 1k FREQUENCY – Hz 10 TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V FREQUENCY = 20Hz CB = 0.1mF 100 RL = 32V PO = 15mW 1k FREQUENCY – Hz VDD = 3.3V 1 10 TA = 1258C VDD = 2.7V AVD = 2 (BTL) RL = 8V FREQUENCY = 1kHz CB = 0.1mF 10k 20k 1k FREQUENCY – Hz TA = 1258C AVD = 2 (BTL) RL = 8V FREQUENCY = 20kHz CB = 0.1mF VDD = 3.3V 1 THD + N –% THD + N –% THD + N –% VDD = 5V 100 Figure 24. THD+N vs. Frequency 1 0.1 0.1 VDD = 2.7V 0.1 VDD = 3.3V VDD = 5V VDD = 5V 0.01 20n 0.1 POUTPUT – W 1 0.01 20n 2 Figure 25. THD+N vs. POUTPUT 0.1 POUTPUT – W 1 0.01 20n 2 10,000 0.5 2 TA = 1258C RL = OPEN 12 8,000 SUPPLY CURRENT – mA SOIC uJA = 1988C/W 1 14 VDD = +5V SUPPLY CURRENT – mA TJ,MAX = 11508C FREE AIR NO HEAT SINK 0.1 POUTPUT – W Figure 27. THD+N vs. POUTPUT Figure 26. THD+N vs. POUTPUT 1.5 POWER DISSIPATION – WATTS 0.01 20 10k 20k Figure 23. THD+N vs. Frequency Figure 22. THD+N vs. Frequency 1 RL = 8V PO = 65mW 0.1 RL = 32V PO = 60mW 0.01 20 TA = 1258C VDD = 2.7V AVD = 10 SINGLE ENDED CB = 0.1mF CC = 1000mF 1 RL = 8V PO = 85mW 0.1 10 10 TA = 1258C VDD = 3.3V AVD = 10 SINGLE ENDED CB = 0.1mF CC = 1000mF THD + N – % 10 6,000 4,000 2,000 10 8 6 4 2 0 –20 0 0 20 40 60 TEMPERATURE – 8C 80 100 Figure 28. Maximum Power Dissipation vs. Ambient Temperature 0 1 2 3 4 SHUTDOWN VOLTAGE AT PIN 1 – V Figure 29. Supply Current vs. Shutdown Voltage –6– 5 0 0 1 2 3 4 SUPPLY VOLTAGE – V 5 6 Figure 30. Supply Current vs. Supply Voltage REV. 0 SSM2211 1.6 80 180 1.4 60 135 1.2 40 90 1.0 20 45 0 0 25 VDD = 2.7V SAMPLE SIZE = 300 0.6 0.4 5V 2.7V 4 8 –40 –90 –60 –135 12 16 20 24 28 32 36 40 44 48 LOAD RESISTANCE – V –80 100 FREQUENCY FREQUENCY 12 8 –20 –10 0 10 20 OUTPUT OFFSET VOLTAGE – mV 30 Figure 34. Output Offset Voltage Distribution 12 8 0 –30 –10 0 10 20 –20 OUTPUT OFFSET VOLTAGE – mV Figure 35. Output Offset Voltage Distribution TA = 1258C VDD = 5V 6 100mV CB = 15 mF AVD = 2 –65 100 1k FREQUENCY – Hz 10k 30k Figure 37. PSRR vs. Frequency REV. 0 400 300 200 100 –60 –70 20 VDD = 5.0V SAMPLE SIZE = 1,700 500 4 4 PSRR – dB 600 16 16 25 Figure 33. Output Offset Voltage Distribution VDD = 5.0V 3.3V SAMPLE SIZE = 300 VDD = 3.3V SAMPLE SIZE = 300 0 –30 10 0 –20 –15 –10 –5 0 5 10 15 20 OUTPUT OFFSET VOLTAGE – mV –180 10M 100M 20 20 –55 10k 100k 1M FREQUENCY – Hz Figure 32. Gain, Phase vs. Frequency (Single Amplifier) Figure 31. POUTPUT vs. Load Resistance –50 1k FREQUENCY 0 –45 15 5 3.3V 0.2 –20 FREQUENCY 0.8 PHASE SHIFT – degrees GAIN – dB OUTPUT POWER – W 20 –7– 30 0 6 7 8 9 10 11 12 13 14 SUPPLY CURRENT – mA Figure 36. Supply Current Distribution 15 SSM2211 SSM2211 PRODUCT OVERVIEW TYPICAL APPLICATION The SSM2211 is a low distortion speaker amplifier that can run from a 1.7 V to 5.5 V supply. It consists of a rail-to-rail input and a differential output that can be driven within 400 mV of either supply rail while supplying a sustained output current of 350 mA. The SSM2211 is unity-gain stable, requiring no external compensation capacitors, and can be configured for gains of up to 40 dB. Figure 38 shows the simplified schematic. RF +5V CC AUDIO INPUT RI CS 6 4 5 SSM2211 20kV 1 8 3 SPEAKER 8V 7 VDD 2 6 CB VIN 20kV SSM2211 4 A1 5 50kV 3 Figure 39 shows how the SSM2211 would be connected in a typical application. The SSM2211 can be configured for gain much like a standard op amp. The gain from the audio input to the speaker is: 50kV 50kV A2 2 8 50kV Figure 39. A Typical Configuration VO1 VO2 AV = 2 × BIAS CONTROL 0.1mF 7 1 SHUTDOWN Figure 38. Simplified Schematic Pin 4 and Pin 3 are the inverting and noninverting terminals to A1. An offset voltage is provided at Pin 2, which should be connected to Pin 3 for use in single supply applications. The output of A1 appears at Pin 5. A second op amp, A2, is configured with a fixed gain of AV = –1 and produces an inverted replica of Pin 5 at Pin 8. The SSM2211 outputs at Pins 5 and 8 produce a bridged configuration output to which a speaker can be connected. This bridge configuration offers the advantage of a more efficient power transfer from the input to the speaker. Because both outputs are symmetric, the dc bias at Pins 5 and 8 are exactly equal, resulting in zero dc differential voltage across the outputs. This eliminates the need for a coupling capacitor at the output. The SSM2211 can achieve 1 W continuous output into 8 Ω, even at ambient temperatures up to +85°C. This is due to a proprietary SOIC package from Analog Devices that makes use of an internal structure called a Thermal Coastline. The Thermal Coastline provides a more efficient heat dissipation from the die than in standard SOIC packages. This increase in heat dissipation allows the device to operate in higher ambient temperatures or at higher continuous output currents without overheating the die. For a standard SOIC package, typical junction to ambient temperature thermal resistance (uJA) is +158°C/W. In a Thermal Coastline SOIC package, uJA is +98°C/W. Simply put, a die in a Thermal Coastline package will not get as hot as a die in a standard SOIC package at the same current output. Because of the large amounts of power dissipated in a speaker amplifier, competitor’s parts operating from a 5 V supply can only drive 1 W into 8 Ω in ambient temperatures less than +44°C, or +111°F. With the Thermal Coastline SOIC package, the SSM2211 can drive an 8 Ω speaker with 1 W from a 5 V supply with ambient temperatures as high as +85°C (+185°F), without a heat sink or forced air flow. RF RI (1) The 3 2 factor comes from the fact that Pin 8 is opposite polarity from Pin 5, providing twice the voltage swing to the speaker from the bridged output configuration. CS is a supply bypass capacitor to provide power supply filtering. Pin 2 is connected to Pin 3 to provide an offset voltage for single supply use, with CB providing a low AC impedance to ground to help power supply rejection. Because Pin 4 is a virtual AC ground, the input impedance is equal to RI. CC is the input coupling capacitor which also creates a high-pass filter with a corner frequency of: f HP = 1 2 πRI × CC (2) Because the SSM2211 has an excellent phase margin, a feedback capacitor in parallel with RF to band-limit the amplifier is not required, as it is in some competitor’s products. Bridged Output vs. Single Ended Output Configurations The power delivered to a load with a sinusoidal signal can be expressed in terms of the signal’s peak voltage and the resistance of the load: 2 PL = VPK 2 RL (3) By driving a load from a bridged output configuration, the voltage swing across the load doubles. An advantage in using a bridged output configuration becomes apparent from Equation 3 as doubling the peak voltage results in four times the power delivered to the load. In a typical application operating from a 5 V supply, the maximum power that can be delivered by the SSM2211 to an 8 Ω speaker in a single ended configuration is 250 mW. By driving this speaker with a bridged output, 1 W of power can be delivered. This translates to a 12 dB increase in sound pressure level from the speaker. –8– REV. 0 SSM2211 The internal power dissipation of the amplifier is the internal voltage drop multiplied by the average value of the supply current. An easier way to find internal power dissipation is to take the difference between the power delivered by the supply voltage source and the power delivered into the load. The waveform of the supply current for a bridged output amplifier is shown in Figure 40. Driving a speaker differentially from a bridged output offers another advantage in that it eliminates the need for an output coupling capacitor to the load. In a single supply application, the quiescent voltage at the output is 1/2 of the supply voltage. If a speaker were connected in a single ended configuration, a coupling capacitor would be needed to prevent dc current from flowing through the speaker. This capacitor would also need to be large enough to prevent low frequency roll-off. The corner frequency is given by: VOUT VPEAK f −3dB Where 1 = 2 π RLCC (4) TIME T RL is the speaker resistance and, CC is the coupling capacitance ISY For an 8 Ω speaker and a corner frequency of 20 Hz, a 1000 µF capacitor would be needed, which is quite physically large and costly. By connecting a speaker in a bridged output configuration, the quiescent differential voltage across the speaker becomes nearly zero, eliminating the need for the coupling capacitor. IDD, PEAK IDD, AVG T Speaker Efficiency and Loudness The effective loudness of 1 W of power delivered into an 8 Ω speaker is a function of the efficiency of the speaker. The efficiency of a speaker is typically rated as the sound pressure level (SPL) at 1 meter in front of the speaker with 1 W of power applied to the speaker. Most speakers are between 85 dB and 95 dB SPL at 1 meter at 1 W. Table I shows a comparison of the relative loudness of different sounds. By integrating the supply current over a period T, then dividing the result by T, IDD,AVG can be found. Expressed in terms of peak output voltage and load resistance: I DD , dB SPL Threshold of Pain Heavy Street Traffic Cabin of Jet Aircraft Average Conversation Average Home at Night Quiet Recording Studio Threshold of Hearing 120 95 80 65 50 30 0 PSY = = 2 VPEAK πRL (5) 2 VDDVPEAK πRL (6) Now, the power dissipated by the amplifier internally is simply the difference between Equation 6 and Equation 3. The equation for internal power dissipated, PDISS, expressed in terms of power delivered to the load and load resistance is: It can easily be seen that 1 W of power into a speaker can produce quite a bit of acoustic energy. PDISS = Power Dissipation Another important advantage in using a bridged output configuration is the fact that bridged output amplifiers are more efficient than single ended amplifiers in delivering power to a load. Efficiency is defined as the ratio of power from the power supply 2 2 × VDD π RL PL − PL The graph of this equation is shown in Figure 41. PL to the power delivered to the load η = . An amplifier PSY with a higher efficiency has less internal power dissipation, which results in a lower die-to-case junction temperature, as compared to an amplifier that is less efficient. This is important when considering the amplifier device’s maximum power dissipation rating versus ambient temperature. An internal power dissipation versus output power equation can be derived to fully understand this. REV. 0 AVG therefore power delivered by the supply, neglecting the bias current for the device is, Table I. Typical Sound Pressure Levels Source of Sound TIME Figure 40. Bridged Amplifier Output Voltage and Supply Current vs. Time –9– (7) SSM2211 1.5 0.35 VDD = 15V VDD = 15V RL = 4V RL = 4V POWER DISSIPATION – W POWER DISSIPATION – W 0.30 1.0 RL = 8V 0.5 0 0.5 1.0 OUTPUT POWER – W RL = 8V 0.10 RL = 16V ∂PDISS 2 × VDD −12 = −1 = 0 PL ∂PL πRL (8) And this occurs when: 2 VDD 2 π 2 RL (9) Using Equation 9 and the power derating curve in Figure 28, the maximum ambient temperature can be easily found. This insures that the SSM2211 will not exceed its maximum junction temperature of 150°C. π RL PL − PL 0.1 0.2 OUTPUT POWER – W 0.3 0.4 The maximum power dissipation for a single ended output is: PDISS ,MAX = VDD 2 (11) 2 π 2 RL Output Voltage Headroom The outputs of both amplifiers in the SSM2211 can come to within 400 mV of either supply rail while driving an 8 Ω load. As compared to other competitors’ equivalent products, the SSM2211 has a higher output voltage headroom. This means that the SSM2211 can deliver an equivalent maximum output power while running from a lower supply voltage. By running at a lower supply voltage, the internal power dissipation of the device is reduced, as can be seen from Equation 9. This extended output headroom, along with the Thermal Coastline package, allows the SSM2211 to operate in higher ambient temperatures than other competitors’ devices. The SSM2211 is also capable of providing amplification even at supply voltages as low as 1.7 V. Of course, the maximum power available at the output is a function of the supply voltage. Therefore, as the supply voltage decreases, so does the maximum power output from the device. Figure 43 shows the maximum output power versus supply voltage at various bridged-tied load resistances. The maximum output power is defined as the point at which the output has 1% THD. The power dissipation for a single ended output application where the load is capacitively coupled is given by: 2 2 × VDD 0 Figure 42. Power Dissipation vs. Single Ended Output Power with (VDD = 5 V) Because the efficiency of a bridged output amplifier (Equation 3 divided by Equation 6) increases with the square root of PL, the power dissipated internally by the device stays relatively flat, and will actually decrease with higher output power. The maximum power dissipation of the device can be found by differentiating Equation 7 with respect to load power, and setting the derivative equal to zero. This yields: ∂PDISS = 0.15 0 1.5 Figure 41. Power Dissipation vs. Output Power with VDD = 5 V PDISS ,MAX = 0.20 0.05 RL = 16V 0 0.25 (10) 1.6 1.4 MAX POUT @ 1% THD – W The graph of Equation 10 is shown in Figure 42. 1.2 RL = 4V 1.0 RL = 8V 0.8 0.6 RL = 16V 0.4 0.2 0 1.5 2.0 2.5 3.0 3.5 4.0 SUPPLY VOLTAGE – V 4.5 5.0 Figure 43. Maximum Output Power vs. VSY –10– REV. 0 SSM2211 To find the appropriate component values, first the gain of A2 must be determined by: To find the minimum supply voltage needed to achieve a specified maximum undistorted output power, simply use Figure 43. For example, an application requires only 500 mW to be output for an 8 Ω speaker. With the speaker connected in a bridged output configuration, the minimum supply voltage required is 3.3 V. AV , MIN = VSY VTHS (12) Shutdown Feature Where, VSY is the single supply voltage and, VTHS is the threshold voltage. The SSM2211 can be put into a low power consumption shutdown mode by connecting Pin 1 to 5 V. In shutdown mode, the SSM2211 has an extremely low supply current of less than 10 nA. This makes the SSM2211 ideal for battery powered applications. AV should be set to a minimum of 2 for the circuit to work properly. Next choose R1 and set R2 to: Pin 1 should be connected to ground for normal operation. Connecting Pin 1 to VDD will mute the outputs and put the SSM2211 into shutdown mode. A pull-up or pull-down resistor is not required. Pin 1 should always be connected to a fixed potential, either VDD or ground, and never be left floating. Leaving Pin 1 unconnected could produce unpredictable results. 2 R2 = R1 1 − AV Find R3 as: Automatic Shutdown Sensing Circuit Figure 44 shows a circuit that can be used to automatically take the SSM2211 in and out of shutdown mode. This circuit can be set to turn the SSM2211 on when an input signal of a certain amplitude is detected. The circuit will also put the SSM2211 into its low-power shutdown mode once an input signal is not sensed within a certain amount of time. This can be useful in a variety of portable radio applications where power conservation is critical. (13) R3 = ( ) R1 × R2 AV − 1 R1 + R2 (14) C1 can be arbitrarily set, but should be small enough to not cause A2 to become capacitively overloaded. R4 and C1 will control the shutdown rate. To prevent intermittent shutdown with low frequency input signals, the minimum time constant should be: R 4 × C1 ≥ R8 10 f LOW (15) VDD Where, fLOW is the lowest input frequency expected. R7 R5 4 C2 R6 R4 A2 1 D1 OP181 C1 R1 R2 In this example a portable radio application requires the SSM2211 to be turned on when an input signal greater than 50 mV is detected. The device should return to shutdown mode within 500 ms after the input signal is no longer detected. The lowest frequency of interest is 200 Hz, and a +5 V supply is being used. 1 8 A1 2 VDD Shutdown Circuit Design Example 5 SSM2211 VDD VIN NOTE: ADDITIONAL PINS OMITTED FOR CLARITY R3 Figure 44. Automatic Shutdown Circuit The input signal to the SSM2211 is also connected to the noninverting terminal of A2. R1, R2, and R3 set the threshold voltage of when the SSM2211 will be taken out of shutdown mode. D1 half-wave rectifies the output of A2, discharging C1 to ground when an input signal greater than the set threshold voltage is detected. R4 controls the charge time of C1, which sets the time until the SSM2211 is put back into shutdown mode after the input signal is no longer detected. R5 and R6 are used to establish a voltage reference point equal to half of the supply voltage. R7 and R8 set the gain of the SSM2211. D1 should be a 1N914 or equivalent diode and A2 should be a rail-to-rail output amplifier, such as an OP181 or equivalent. This will ensure that C1 will discharge sufficiently to bring the SSM2211 out of shutdown mode. The minimum gain of the shutdown circuit from Equation 12 is AV = 100. R1 is set to 100 kΩ, and using Equation 13 and Equation 14, R2 = 98 kΩ and R3 = 4.9 MΩ. C1 is set to 0.01 µF, and based on Equation 15, R4 is set to 10 MΩ. To minimize power supply current, R5 and R6 are set to 10 MΩ. The above procedure will provide an adequate starting point for the shutdown circuit. Some component values may need to be adjusted empirically to optimize performance. Turn On Popping Noise During power-up or release from shutdown mode, the midrail bypass capacitor, CB, determines the rate at which the SSM2211 starts up. By adjusting the charging time constant of CB, the start-up pop noise can be pushed into the sub-audible range, greatly reducing startup popping noise. On power-up, the midrail bypass capacitor is charged through an effective resistance of 25 kΩ. To minimize start-up popping, the charging time constant for CB should be greater than the charging time constant for the input coupling capacitor, CC. CB × 25 kΩ > CC RI REV. 0 –11– (16) SSM2211 For an application where R1 = 10 kΩ and CC = 0.22 µF, the midrail bypass capacitor, CB, should be at least 0.1 µF to minimize start-up popping noise. Selecting CB to be 2.2 µF for a practical value of capacitor will minimize start-up popping noise. SSM2211 Amplifier Design Example VDD R1 RF CC CB Max. TA To summarize the final design: Given: Maximum Output Power Input Impedance Load Impedance Input Level Bandwidth 1W 20 kΩ 8Ω 1 V rms 20 Hz – 20 kHz ± 0.25 dB 5V 20 kΩ 28 kΩ 2.2 µF 2.2 µF +85°C Single Ended Applications The configuration shown in Figure 39 will be used. The first thing to determine is the minimum supply rail necessary to obtain the specified maximum output power. From Figure 43, for 1 W of output power into an 8 Ω load, the supply voltage must be at least 4.6 V. A supply rail of 5 V can be easily obtained from a voltage reference. The extra supply voltage will also allow the SSM2211 to reproduce peaks in excess of 1 W without clipping the signal. With VDD = 5 V and RL = 8 Ω, Equation 9 shows that the maximum power dissipation for the SSM2211 is 633 mW. From the power derating curve in Figure 28, the ambient temperature must be less than +85°C. There are applications where driving a speaker differentially is not practical. An example would be a pair of stereo speakers where the minus terminal of both speakers is connected to ground. Figure 45 shows how this can be accomplished. 10kV +5V 10kV AUDIO INPUT The required gain of the amplifier can be determined from Equation 17: 6 4 5 0.47mF SSM2211 1 8 3 7 470mF 2 AV = PL RL VIN , rms = 2.8 (17) 0.1mF 250mW SPEAKER (8V) Figure 45. A Single Ended Output Application R A From Equation 1, F = V , or RF = 1.4 × R1. Since the deR1 2 sired input impedance is 20 kΩ, R1 = 20 kΩ and R2 = 28 kΩ. It is not necessary to connect a dummy load to the unused output to help stabilize the output. The 470 µF coupling capacitor creates a high pass frequency cutoff as given in Equation 4 of 42 Hz, which is acceptable for most computer speaker applications. The final design step is to select the input capacitor. Because adding an input capacitor, CC, high pass filter, the corner frequency needs to be far enough away for the design to meet the bandwidth criteria. For a 1st order filter to achieve a passband response within 0.25 dB, the corner frequency should be at least 4.14 times away from the passband frequency. So, (4.14 3 fHP) < 20 Hz. Using Equation 2, the minimum size of input capacitor can be found: CC > 1 20 Hz 2π 20 kΩ 4.14 ( ) The overall gain for a single ended output configuration is AV = RF/R1, which for this example is equal to 1. Driving Two Speakers Single Endedly It is possible to drive two speakers single endedly with both outputs of the SSM2211. 20kV +5V (18) 20kV AUDIO INPUT 25 kΩ 1 8 7 2 0.1mF 470mF RIGHT SPEAKER (8V) Figure 46. SSM2211 Used as a Dual Speaker Amplifier Equation 16 shows an appropriate value for CB to reduce startup popping noise: (2.2 µF )(20 kΩ) = 1.76 µF LEFT SPEAKER (8V) SSM2211 3 The gain-bandwidth product for each internal amplifier in the SSM2211 is 4 MHz. Because 4 MHz is much greater than 4.14 3 20 kHz, the design will meet the upper frequency bandwidth criteria. The SSM2211 could also be configured for higher differential gains without running into bandwidth limitations. CB > 5 1mF So CC > 1.65 µF. Using a 2.2 µF is a practical choice for CC. 470mF 6 4 (19) Each speaker is driven by a single ended output. The trade-off is that only 250 mW sustained power can be put into each speaker. Also, a coupling capacitor must be connected in series with each of the speakers to prevent large DC currents from flowing through the 8 Ω speakers. These coupling capacitors –12– REV. 0 SSM2211 must connect the ground lead of the test instrument to either output signal pins, a power line isolation transformer must be used to isolate the instrument ground from power supply ground. will produce a high pass filter with a corner frequency given by Equation 4. For a speaker load of 8 Ω and a coupling capacitor of 470 µF, this results in a –3 dB frequency of 42 Hz. Because the power of a single ended output is one quarter that of a bridged output, both speakers together would still be half as loud (–6 dB SPL) as a single speaker driven with a bridged output. Recall that V = P × R , so for PO = 1 W and RL = 8 Ω, V = 2.8 V rms, or 8 V p-p. If the available input signal is 1.4 V rms or more, use the board as is, with RF = RI = 20 kΩ. If more gain is needed, increase the value of RF to obtain the desired gain. The polarity of the speakers is important, as each output is 180° out of phase with the other. By connecting the minus terminal of Speaker 1 to Pin 5, and the plus terminal of Speaker 2 to Pin 8, proper speaker phase can be established. When you have determined the closed-loop gain required by your source level, and can develop 1 W across the 8 Ω load resistor with the normal input signal level, replace the resistor with your speaker. Your speaker may be connected across the VO1 and VO2 posts for bridged mode operation only after the 8 Ω load resistor is removed. For no phase inversion, VO2 should be connected to the (+) terminal of the speaker. The maximum power dissipation of the device can be found by doubling Equation 11, assuming both loads are equal. If the loads are different, use Equation 11 to find the power dissipation caused by each load, then take the sum to find the total power dissipated by the SSM2211. Evaluation Board VO2 An evaluation board for the SSM2211 is available. Contact your local sales representative or call 1-800-ANALOGD for more information. CH A 5 2.5V COMMON MODE SSM2211 V+ R1 51kV 8V 1W GND PROBES 8 + C2 10mF CH B C1 0.1mF VO1 SHUTDOWN OSCILLOSCOPE 6 8 ON AUDIO INPUT J1 V02 Figure 48. Using an Oscilloscope to Display the Bridged Output Voltage 1 3 + CW CIN 1mf RIN 20kV To use the SSM2211 in a single ended output configuration, replace J1 and J2 jumpers with electrolytic capacitors of a suitable value, with the NEGATIVE terminals to the output terminals VO1 and VO2. The single ended loads may then be returned to ground. Note that the maximum output power is reduced to 250 mW, one quarter of the rated maximum, due to the maximum swing in the non-bridged mode being one-half, and power being proportional to the square of the voltage. For frequency response down 3 dB at 100 Hz, a 200 µF capacitor is required with 8 Ω speakers. RL 1W 8V 2 SSM2211 VOLUME 20kV POT. 5 4 7 J2 V01 RF 20kV C1 0.1mF Figure 47. Evaluation Board Schematic The SSM2211 evaluation board also comes with a SHUTDOWN switch which allows the user to switch between ON (normal operation) and the power conserving shutdown mode. The voltage gain of the SSM2211 is given by Equation 20 below: AV = 2 × RF RIN (20) If desired, the input signal may be attenuated by turning the 10 kΩ potentiometer in the CW direction. CIN isolates the input common mode voltage (V+/2) present at Pin 2 and 3. With V+ = 5 V, there is +2.5 V common-mode voltage present at both output terminals VO1 and VO2 as well. CAUTION: The ground lead of the oscilloscope probe, or any other instrument used to measure the output signal, must not be connected to either output, as this would short out one of the amplifier’s outputs and possibly damage the device. A safe method of displaying the differential output signal using a grounded scope is shown in Figure 48. Simply connect the Channel A probe to VO2 terminal post, connect the Channel B probe to VO1 post, invert Channel B and add the two channels together. Most multichannel oscilloscopes have this feature built in. If you REV. 0 CH B DISPLAY INV. ON A+B Printed Circuit Board Layout Consideration All surface mount packages rely on the traces of the PC board to conduct heat away from the package. In standard packages, the dominant component of the heat resistance path is the plastic between the die attach pad and the individual leads. In typical thermally enhanced packages, one or more of the leads are fused to the die attach pad, significantly decreasing this component. To make the improvement meaningful, however, a significant copper area on the PCB must be attached to these fused pins. The patented Thermal Coastline lead frame design used in the SSM2211 (Figure 49) uniformly minimizes the value of the dominant portion of the thermal resistance. It ensures that heat is conducted away by all pins of the package. This yields a very low, 98°C/W, thermal resistance for an SO-8 package, without any special board layer requirements, relying on the normal traces connected to the leads. The thermal resistance can be decreased by approximately an additional 10% by attaching a few –13– SSM2211 square cm of copper area to the ground pins. It is recommended that the solder mask and/or silk screen on the PCB traces adjacent to the SSM2211 pins be deleted, thus reducing further the junction to ambient thermal resistance of the package. COPPER LEAD-FRAME 1 8 2 7 COPPER PADDLE 3 6 4 5 Figure 49. Thermal Coastline –14– REV. 0 SSM2211 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead SOIC (S0-8) 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) 8 5 1 4 PIN 1 0.0688 (1.75) 0.0532 (1.35) 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 0.2440 (6.20) 0.2284 (5.80) 0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC 0.0196 (0.50) x 45° 0.0099 (0.25) 0.0098 (0.25) 0.0075 (0.19) 8° 0° 0.0500 (1.27) 0.0160 (0.41) 8-Lead Plastic DIP (N-8)* 0.430 (10.92) 0.348 (8.84) 8 5 0.280 (7.11) 0.240 (6.10) 1 4 PIN 1 0.210 (5.33) MAX 0.060 (1.52) 0.015 (0.38) 0.325 (8.25) 0.300 (7.62) 0.130 (3.30) MIN 0.160 (4.06) 0.115 (2.93) 0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC SEATING PLANE *Special order only. REV. 0 –15– 0.195 (4.95) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) –16– PRINTED IN U.S.A. C3238–8–10/97