Doc# ft690- 0502273076 December 15, 2006 ft690 2W Mono BTL Audio Power Amplifier General Description Key Specifications The ft690 is an audio power amplifier primarily designed for demanding applications in mobile phones and other portable communication device applications. It is capable of delivering 1.25 watts of continuous average power to an 8Ω BTL load and 2 watts of continuous average power (DFN only) to a 4Ω BTL load with less than 1% distortion (THD+N+N) from a 5VDC power supply. Improved PSRR at 217Hz & 1KHz 66dB Power Output at 5.0V, 1% THD+N, 4Ω (QFN only) 2W (typ) Power Output at 5.0V, 1% THD+N, 8Ω 1.25W (typ) Power Output at 3.0V, 1% THD+N, 4Ω 600mW (typ) Power Output at 3.0V, 1% THD+N, 8Ω 425mW (typ) Shutdown Current 0.1μA (typ) The ft690 was designed specifically to provide high quality output power with a minimal amount of external components. The ft690 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The ft690 features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables the shutdown pin to be driven in a likewise manner to enable shutdown. The ft690 contains advanced pop & click circuitry which eliminates noise which would otherwise occur during turn-on and turn-off transitions. The ft690 is unity-gain stable and can be configured by external gain-setting resistors. Features Available in space-saving packages: DFN, MSOP, WCSP Ultra low current shutdown mode Improved pop & click circuitry eliminates noise during turn-on and turn-off transitions 2.2 - 5.5V operation No output coupling capacitors, snubber networks or bootstrap capacitors required Unity-gain stable External gain configuration capability User selectable shutdown High or Low logic Level Applications Mobile Phones PDAs Portable electronic device Application Circuit Figure 1.Typical Audio Amplifier Application Circuit (DFN) 1 ft690_DS_2.1 Figure 2.Typical Audio Amplifier Application Circuit (MSOP and WCSP) ORDERING INFORMATION P/N TEMP RANGE PIN-PACKAGE GAIN(dB) ft690D -40°C to +85°C 10pin DFN Adj. ft690M -40°C to +85°C 8pin MSOP Adj. Ft690W -40°C to +85°C 9pin WCSP Adj. Ordering Information continued at end of data sheet. Pin Configurations and Selector Guide appear at end of data sheet. ABSOLUTE MAXIMUM RATINGS Unit Supply voltage, VDD 6.0 V Storage Temperature −65°C to +150°C Input Voltage −0.3V to VDD +0.3V Power Dissipation Internally Limited ESD Susceptibility 2000V Junction Temperature 150°C θJC (MSOP) 56°C/W θJA (MSOP) 190°C/W θJC (WCSP) 180°C/W θJA (DFN) 63°C/W θJC (DFN) 12°C/W Lead temperature 1,6 mm (1/16 Inch) from case for 10 seconds 260°C ft690_DS_2.1 RECOMMENDED OPERATING CONDITIONS MIN Supply voltage, VDD YP 2.5 High-level input voltage, VIH SHUTDOWN Low-level input voltage, VIL SHUTDOWN Common-mode input voltage, VIC VDD = 2.5 V, 5.5 V, CMRR ≤ -60 dB MAX UNIT 5.5 V 2 V 0.8 V 0.5 VDD-0.8 V Operating free-air temperature, TA -40 85 °C Load impedance, ZL 6.4 8 Ω ELECTRICAL CHARACTERISTICS VDD=5V TA=25°C Symbol Parameter IDD Quiescent Power Supply Current ISD VSDIH VSDIL VSDIH VSDIL VOS Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage ROUT Resistor Output to GND TWU THD+N Output Power (8 Ω) (4Ω) Wake-up time Total Harmonic Distortion+Noise PSRR Power Supply Rejection Ratio PO VDD=3V Symbol Parameter Quiescent Power Supply Current ISD VSDIH VSDIL VSDIH VSDIL VOS Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage 8.5 THD+N=1% (max); f=1kHz THD+N=1% (max); f=1kHz PO = 0.5Wrms; f=1kHz Vripple=200mV sine p-p Input terminated with 10 Ω Conditions VIN=0V, IO=0A, No Load VIN=0V, IO=0A, 8 Ω Load VSD= VSD MODE (WCSP only) VSD MODE = VDD VSD MODE = VDD VSD MODE = GND VSD MODE = GND Resistor Output to GND TWU THD+N Output Power (8 Ω) Output Power (4 Ω) Wake-up time Total Harmonic Distortion+Noise PSRR Power Supply Rejection Ratio PO Typical 2.5 3 0.1 1.5 1.3 1.5 1.3 7 1.25 2 130 0.2 66(f=217Hz) 76(f=1kHz) Limit 7 10 2.0 50 9.7 7.0 0.9 Units(Limits) mA (max) mA (max) μA (max) V V V V mV (max) K Ω (max) K Ω (min) W (min) W Ms % 55 dB (min) Limit 7 9 2.0 Units(Limits) mA (max) mA (max) μA (max) V V V V mV (max) K Ω (max) K Ω (min) mW mW Ms % TA=25°C IDD ROUT Conditions VIN=0V, IO=0A, No Load VIN=0V, IO=0A, 8 Ω Load VSD= VSD MODE (WCSP only) VSD MODE = VDD VSD MODE = VDD VSD MODE = GND VSD MODE = GND Typical 1.6 2 0.1 1.1 0.9 1.3 1.0 7 8.5 THD+N=1% (max); f=1kHz THD+N=1% (max); f=1kHz PO = 0.25Wrms; f=1kHz Vripple=200mV sine p-p Input terminated with 10 Ω 425 600 80 0.1 66(f=217Hz) 76(f=1kHz) 50 9.7 7.0 55 dB (min) ft690_DS_2.1 VDD=2.6V Symbol TA=25°C Parameter IDD Quiescent Power Supply Current ISD VSDIH VSDIL VSDIH VSDIL VOS Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage ROUT Resistor Output to GND TWU THD+N+N Output Power (8 Ω) Output Power (4 Ω) Wake-up time Total Harmonic Distortion+Noise PSRR Power Supply Rejection Ratio PO Conditions VIN=0V, IO=0A, No Load VIN=0V, IO=0A, 8 Ω Load VSD= VSD MODE (WCSP only) VSD MODE = VDD VSD MODE = VDD VSD MODE = GND VSD MODE = GND Typical 1.5 2 0.1 1.0 0.9 1.2 1.0 5 8.5 THD+N=1% (max); f=1kHz THD+N=1% (max); f=1kHz 300 400 70 0.1 66(f=217Hz) 76(f=1kHz) PO = 0.15Wrms; f=1kHz Vripple=200mV sine p-p Input terminated with 10 Ω Limit 50 9.7 7.0 55 PIN DESCRIPTION DFN Package MSOP Package Top View Order Number ft690D Top View Order Number ft690M WCSP Package Top View Order Number ft690W Units(Limits) mA (max) mA (max) μA (max) V V V V mV (max) K Ω (max) K Ω (min) mW mW Ms % dB (min) ft690_DS_2.1 Package Shutdown Mode Typical Power Output at 5V, 1% THD+N DFN MSOP WCSP Selectable Low 2W (RL=4) 1.25W (RL=8Ω) Low 1.25W (RL=8) A SD_MODE select pin determines the Shutdown Mode for the DFN package, whether it is an Asserted High or an Asserted Low device, to activate shutdown. The SD_MODE select pin is with the MSOP and WCSP packaged devices, shutdown occurs only with an low assertion. Typical Performance Characteristics LD and MH Specific Characteristics THD+N+N vs Frequency Vdd=3V, RL=8Ω , Po=0.25W 10 10 1 1 THD+N (%) THD+N (%) THD+N+N vs Frequency Vdd=5V, RL=8Ω , Po=0.5W 0.1 0.1 0.01 0.01 10 100 1000 Frequency (Hz) 10000 100000 10 100 1000 Frequency (Hz) 10000 100000 ft690_DS_2.1 THD+N+N vs Frequency Vdd=2.6V, RL=8Ω , Po=0.15W 10 THD+N (%) 1 0.1 0.01 10 100 1000 10000 100000 Frequency (Hz) THD+N+N vs Output Power Vdd=5V, RL=8Ω , f=1KHz THD+N (%) 10 1 0.1 0.01 0.01 0.1 1 10 Output Power (W) THD+N+N vs Output Power Vdd=3V, RL=8Ω , f=1KHz THD+N (%) 10 1 0.1 0.01 0.01 0.1 Output Power (W) 1 ft690_DS_2.1 THD+N+N vs Output Power Vdd=2.6V, RL=8 Ω , f=1KHz THD+N (%) 10 1 0.1 0.01 0.01 0.1 1 Output Power (W) PSRR vs Frequency Vdd=3V, RL=8Ω , Input=10Ω 0 0 -10 -10 -20 -20 -30 -30 PSRR (dB) PSRR (dB) PSRR vs Frequency Vdd=5V, RL=8Ω , Input=10Ω -40 -50 -60 -40 -50 -60 -70 -70 -80 -80 -90 -90 -100 -100 10 100 1000 10000 100000 10 100 Frequency (Hz) 1000 10000 100000 Frequency (Hz) Power Dissipation vs Output Power Vdd=5V, RL=8Ω PSRR vs Frequency Vdd=2.6V, RL=8Ω , Input=10Ω 1 0 Power Dissipation (W) -10 -20 PSRR (dB) -30 -40 -50 -60 -70 0.8 0.6 0.4 0.2 -80 -90 0 -100 10 100 1000 Frequency (Hz) 10000 100000 0 0.5 1 Output Power (W) 1.5 2 ft690_DS_2.1 Power Dissipation vs Output Power Vdd=3V, RL=8Ω Power Dissipation vs Output Power Vdd=2.6V, RL=8 Ω 0.3 0.35 Power Dissipation (W) Power Dissipation (W) 0.4 0.3 0.25 0.2 0.15 0.1 0 0.15 0.1 0 0 0.2 0.4 0.6 0.8 Frequency Response vs Input Capacitor Size Vdd=5V, RL=8 Ω , Cap=0.44uF 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 100 1000 Frequency (Hz) 10000 0 0.1 0.2 0.3 Output Power (W) Output Power (W) Output Level (dB) 0.2 0.05 0.05 10 0.25 100000 0.4 0.5 ft690_DS_2.1 Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the ft690 has two internal operational amplifiers. 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 20kΩ 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 by 180°. Consequently, the differential gain for the IC is AVD= 2 *(Rf/Ri) By driving the load differentially through outputs Vo1 and Vo2, an 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. 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, please refer to Audio Power Amplifier Design section. A bridge configuration, such as the one used in ft690, also creates a second advantage over single-ended amplifiers. 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 possible 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. Since the ft690 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4*(VDD)2/(2π2RL) (1) It is critical that the maximum junction temperature TJMAX of 150°C is not exceeded. TJMAX can be determined from the power derating curves by using PDMAX and the PC board foil area. By adding copper foil, the thermal resistance of the application can be reduced from the free air value of θJA, resulting in higher PDMAX values without thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the leads connected to the ft690. It is especially effective when connected to VDD, GND, and the output pins. Refer to the application information on the ft690 reference design board for an example of good heat sinking. If TJMAX still exceeds 150°C, then additional changes must be made. These changes can include reduced supply voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of output power. POWER SUPPLY BYPASSING As with any 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. Typical applications employ a 5V 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 ft690. The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click and pop performance, system cost, and size constraints. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the ft690 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. In addition, the ft690 contains a Shutdown Mode pin (DFN only), allowing the designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply be tied permanently to either VDD or GND to set the ft690 as either a "shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the ft690 enters shutdown mode whenever the two pins are in the same logic state. The MSOP package lacks this Shutdown Mode feature, and is permanently fixed as a ‘Shutdown-low’ device. It is best to switch between ground and supply for maximum performance. While the device may be disabled with shutdown voltages in between ground and supply, the idle current may be greater than the typical value of 0.1μA. In either case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which provides a quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction with an external pull-up resistor (or pull-down, depending on shutdown high or low application). This scheme guarantees that the shutdown pin will not float, thus preventing unwanted state changes. PROPER SELECTION COMPONENTS OF EXTERNAL Proper selection of external components in applications using integrated power amplifiers is critical to optimize device and system performance. While the ft690 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The ft690 is unity-gain stable which gives the designer maximum system flexibility. The ft690 should be used in low gain configurations to minimize THD+N+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 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 for a few distinct reasons. SELECTION OF INPUT CAPACITOR SIZE Large input capacitors are both expensive and space hungry for portable designs. 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 100Hz to 150Hz. Thus, using a large input capacitor may not increase actual system performance. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci. 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. ft690_DS_2.1 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 ft690 turns on. The slower the ft690’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 Ci (in the range of 0.1μF to 0.39μF), should produce a 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 1.0μF is recommended in all but the most cost sensitive designs. AUDIO POWER AMPLIFIER DESIGN A 1W/8Ω Audio Amplifier Given: Power Output 1Wrms Load Impedance 8Ω Input Level 1Vrms Input Impedance Bandwidth 20kΩ 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. 5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the ft690 to reproduce peaks in excess of 1W without producing audible distortion. 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 2. (2) Rf/Ri = AVD/2 From Equation 2, the minimum AVD is 2.83; use AVD = 3. Since the desired input impedance was 20kΩ, and with a AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results in an allocation of Ri = 20kΩ and Rf = 30kΩ. The final design step is to address the bandwidth requirements ft690_DS_2.1 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. fL = 100Hz/5 = 20Hz fH = 20kHz * 5 = 100kHz Ri in conjunction with Ci create a highpass filter. The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain, AVD. With a AVD = 3 and fH = 100kHz, the resulting GBWP = 300kHz which is much smaller than the ft690 GBWP of 2.5MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the ft690 can still be used without running into bandwidth limitations Ci ≥ 1/(2π*20kΩ*20Hz) = 0.397μF; use 0.39μF Figure 3. HIGHER GAIN AUDIO AMPLIFIER oscillations. Care should be taken when calculating the The ft690 is unity-gain stable and requires no external -3dB frequency in that an incorrect combination of R3 components besides gain-setting resistors, an input coupling capacitor, and proper supply bypassing in the and C4 will cause rolloff before 20kHz. A typical typical application. However, if a closed-loop differential combination of feedback resistor and capacitor that will gain of greater than 10 is required, a feedback capacitor not produce audio band high frequency rolloff is R3 = (C4) may be needed as shown in Figure 2 to bandwidth 20kΩ and C4 = 25pf. These components result in a -3dB limit the amplifier. This feedback capacitor creates a low point of approximately 320kHz. pass filter that eliminates possible high frequency Figure 4. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR ft690 ft690_DS_2.1 PHYSICAL DIMENSIONS ft690_DS_2.1 Figure 5. DFN Package Physical Dimension ft690_DS_2.1 Figure 6. MSOP Package Physical Dimension Figure 7. WCSP Package Physical Dimension ft690_DS_2.1 IMPORTANT NOTICE 1. Disclaimer: The information in document is intended to help you evaluate this product. 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