LP42005 General Description Features The LP42005 is a high efficiency, 1.5W mono class-D audio power amplifier. A low noise, filterless PWM architecture eliminates the output filter, reducing external component count, system cost, and simplifying design. Operating in a single 5V supply, LP42005 is capable of driving 8Ω speaker load at a continuous average output of 1.5W/10% THD+N or 1.3W/1% THD+N. The LP42005 has high efficiency with speaker load compared to a typical class AB amplifier. With a 3.6V supply driving an 8Ω speaker , the efficiency for a 400mW power level is 84%. In cellular handsets, the earpiece, speaker phone, and melody ringer can each be driven by the LP42005. The gain of LP42005 is externally configurable which allows independent gain control from multiple sources by summing signals from seperate sources. The LP42005 is available in DFN packages. Ordering Information LP42005 - □ □ □ F :PB-Free Package QV: DFN-8 Efficiency at 3.6V With an 8-Ω Speaker: − 84% at 400 mW − 80% at 100 mW Low 2.8-mA Quiescent Current and 0.5-µA Shutdown Current 2.5V to 5.5V Wide Supply Voltage Optimized PWM Output Stage Eliminates LC Output Filter Improved PSRR (−72 dB) Eliminates Need for a Voltage Regulator Fully Differential Design Reduces RF Rectification and Eliminates Bypass Capacitor Improved CMRR Eliminates Two Input Coupling Capacitors Internally Generated 250-kHz Switching Frequency Integrated Pop and Click Suppression Circuitry 3mm × 3mm DFN-8 package RoHS compliant and 100% lead(Pb)-free Applications Portable Media Players/MP3 players Cellular and Smart mobile phone DSC Toys Pin Configurations Marking Information Please view website. DFN-8 LP42005-datasheet Feb.-2006 1 -1 LP42005 Typical Application Circuit Audio Amplifier with Differential Input Functional Pin Description PIN PIN I/O SHUTDOWN 1 I shutdown mode when a low level is applied on this pin NC 2 I NC IN+ 3 I Positive input of the first amplifier. IN- 4 I Negative input of the first amplifier,. VO+ 5 O Positive BTL output VDD 6 I Analog VDD input supply. GND 7 VO2 8 LP42005-datasheet I DESCRIPTION Ground connection for circuitry. O Feb.-2006 Positive output of the LP42005. 2 -2 LP42005 Absolute Maximum Ratings LP42005-datasheet Feb.-2006 3 -3 LP42005 LP42005-datasheet Feb.-2006 4 -4 LP42005 Typical Operating Characteristics LP42005-datasheet Feb.-2006 5 -5 LP42005 LP42005-datasheet Feb.-2006 6 -6 LP42005 LP42005-datasheet Feb.-2006 7 -7 LP42005 LP42005-datasheet Feb.-2006 8 -8 LP42005 Application information Fully differential amplifier The LP42005 is a fully differential amplifier with differential inputs and outputs. The fully differential amplifier consists of a differential amplifier and a common-mode amplifier. The differential amplifier ensures that the amplifier outputs a differential voltage on the output that is equal to the differential input times the gain. The common-mode feedback ensures that the common-mode voltage at the output is biased around VDD/2 regardless of the common-mode voltage at the input. The fully differential LP42005 can still be used with a single-ended input; however, the LP42005 should be used with differential inputs when in a noisy environment, like a wireless handset, to ensure maximum noise rejection. Figure 23 shows the LP42005 typical schematic with differential inputs and Figure 24 shows the LP42005 with differential inputs and input capacitors, and Figure 25 shows the LP42005 with single-ended inputs. Differential inputs should be used whenever possible because the single-ended inputs are much more susceptible to noise. Advantages of Fully Differential Amplifiers Input-coupling capacitors not required: (1) CI is only needed for single-ended input or if VICM is not between 0.5 V and VDD – 0.8 V. CI = 3.3 nF (with RI = 150 kΩ) gives a high-pass corner frequency of 321 Hz. The fully differential amplifier allows the inputs to be biased at voltage other than mid-supply. For example, if a codec has a mid-supply lower than the mid-supply of the LP42005, the common-mode feedback circuit will adjust, and the LP42005 outputs will still be biased at mid-supply of the LP42005. The inputs of the LP42005 can be biased from 0.5V to DD – 0.8 V. If the inputs are biased outside of that range, input-coupling capacitors are required. Midsupply bypass capacitor, C(BYPASS), not required: The fully differential amplifier does not require a bypass capacitor. This is because any shift in the midsupply affects both positive and negative channels equally and cancels at the differential output. Table1. Typical component Values REF DES VALUE RI 150kΩ ( ± 0.5%) CS 1µF (+22%,-80%) CI (1) 3.3nF ( ± 10%) Figure 23. Typical Application Schematic With Differential Input for a Wireless Phone Better RF−immunity: -GSM handsets save power by turning on and shutting off the RF transmitter at a rate of 217 Hz. The transmitted signal is picked-up on input and output traces. The fully differential amplifier cancels the signal much better than the typical audio amplifier. Figure 24. Typical Application Schematic With Differential Input and Input Capacitors Component Selection LP42005-datasheet Feb.-2006 9 -9 LP42005 Figure 25. Typical Application Schematic With Single-Ended Input transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically1 µF, placed as close as possible to the device DD lead works best. Placing this decoupling capacitor close to the LP42005 is very important for the efficiency of the class-D amplifier, because any resistance or inductance in the trace between the device and the capacitor can cause a loss in efficiency. For filtering lower-frequency noise signals, a 10µF or greater capacitor placed near the audio power amplifier would also help, but it is not required in most applications because of the high PSRR of this device. Input Capacitors (CI) Input Resistors (RI) The input resistors (RI) set the gain of the amplifier according to equation (1). Resistor matching is very important in fully differential amplifiers. The balance of the output on the reference voltage depends on matched ratios of the resistors. CMRR, PSRR, and cancellation of the second harmonic distortion diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or better to keep the performance optimized. Matching is more important than overall tolerance. Resistor arrays with 1% matching can be used with a tolerance greater than 1%. Place the input resistors very close to the LP42005 to limit noise injection on the high-impedance nodes. For optimal performance the gain should be set to 2 V/V or lower. Lower gain allows the LP42005 to operate at its best, and keeps a high voltage at the input making the inputs less susceptible to noise. Decoupling Capacitor (CS) The LP42005 is a high-performance class-D audio amplifier that requires adequate power supply decoupling to ensure the efficiency is high and total harmonic distortion (THD) is low. For higher frequency LP42005-datasheet Feb.-2006 The LP42005 does not require input coupling capacitors if the design uses a differential source that is biased from 0.5 Vto VDD – 0.8 V (shown in Figure 23). If the input signal is not biased within the recommended common −mode input range, if needing to use the input as a high pass filter (shown in Figure 24), or if using a single-ended source (shown in Figure 25), input coupling capacitors are required. The input capacitors and input resistors form a high-pass filter with the corner frequency, fC, determined in equation (2). The value of the input capacitor is important to consider as it directly affects the bass (low frequency) performance of the circuit. Speakers in wireless phones cannot usually respond well to low frequencies, so the corner frequency can be set to block low frequencies in this application. Equation (3) is reconfigured to solve for the input coupling capacitance. If the corner frequency is within the audio band, the capacitors should have a tolerance of ± 10% or better, because any mismatch in capacitance causes an impedance mismatch at the corner frequency and below. For a flat low-frequency response, use large input coupling capacitors (1 µF). However, 10 -10 LP42005 in a GSM phone the ground signal is fluctuating at 217 Hz, but the signal from the codec does not have the same 217 Hz fluctuation. The difference between the two signals is amplified, sent to the speaker, and heard as a 217 Hz hum. Summing Input Signals Most wireless phones or PDAs need to sum signals at the audio power amplifier or just have two signal sources that need separate gain. The LP42005 makes it easy to sum signals or use separate signal sources with different gains. Many phones now use the same speaker for the earpiece and ringer, where the wireless phone would require a much lower gain for the phone earpiece than for the ringer. PDAs and phones that have stereo headphones require summing of the right and left channels to output the stereo signal to the mono speaker. LP42005-datasheet Feb.-2006 11 -11 LP42005 Summing Two Single-Ended Input Signals Four resistors and three capacitors are needed for summing single-ended input signals. The gain and corner frequencies (fc1 and fc2) for each input source can be set independently (see equations (11) through (14), and Figure 28). Resistor, RP, and capacitor, CP, are needed on the IN+ terminal to match the impedance on the IN− terminal. The single-ended inputs must be driven by low impedance sources even if one of the inputs is not outputting an ac signal. Figure 28. Application Schematic With LP42005 . LP42005-datasheet Feb.-2006 12 -12 LP42005 Packing information LP42005-datasheet Feb.-2006 13 -13