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ISL54002IRTZ Scheda tecnica(PDF) 8 Page - Intersil Corporation |
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ISL54002IRTZ Scheda tecnica(HTML) 8 Page - Intersil Corporation |
8 / 11 page 8 FN6458.2 October 17, 2007 Detailed Description The Intersil ISL54000, ISL54001, ISL54002 family of devices are integrated audio power amplifier systems designed to drive 8 Ω speaker loads. They can operate with a supply voltage of +2.7V to +5V and provide good quality audio, while requiring minimal external components. Its low 0.4% THD+N while driving 800mW into an 8 Ω speaker ensures clean, low distortion amplification of the audio signals. The devices are offered in a 20 Ld 4x4 TQFN package. Targeted applications include handheld equipment such as cell-phones, MP3 players, and games/toys. The ISL54000, ISL54001, ISL54002 parts contain two class AB bridge-tied (BTL) type power amplifiers for driving stereo 8 Ω speakers. When powered with a 5V supply, each BTL is capable of delivering 941mW (typ) of continuous average power to an 8 Ω speaker load with 1% THD+N performance. When the speaker load is connected across the positive and negative terminals of the BTL driver, the voltage is doubled across the load and the power is quadrupled. The ISL54001 and ISL54002 feature a 2:1 stereo input multiplexer front-end. This allows selection between two stereo sources. The INS control pin determines which stereo input is active. Applying a logic “0” to the INS control pin selects stereo input 1 (R1 and L1). Applying a logic “1” to the INS control pin selects stereo input 2 (R2 and L2). The ISL54002 has the capability of mixing the two stereo inputs. When in MIX Mode (MIX = “1”) the ISL54002 mixes the R1 input with the R2 input and sends the combined signal to the OUTR_ BTL driver and it mixes the L1 input with the L2 input and sends the combined signal to the OUTL_ BTL driver. All devices in this family feature low power shutdown, thermal overload protection and click/pop suppression. The click and pop circuitry prohibits switching between input channels until the audio input signals are at their lowest point, which eliminates audible transients in the speakers when changing audio input sources. The click/pop circuitry also keeps speaker transients to an inaudibile level when entering and leaving shutdown. Typical application circuits and block diagrams for each device in the family are on page 6 and 7. DC Bias Voltage The ISL54000, ISL54001, ISL54002 have internal DC bias circuitry, which DC offsets the incoming audio signal at VDD/2. When using a 5V supply, the DC offset will be 2.5V. When using a 3.6V supply, the DC offset will be 1.8V. Since the signal gets biased internally at VDD/2, the audio signals need to be AC coupled to the inputs of the device. The value of the AC coupling capacitor depends on the low frequency range required for the application. A capacitor of 0.22µF will pass a signal as low as 7.2Hz. The formula required to calculate the capacitor value is shown in Equation 1: The 100kΩ is the impedance looking into the input of the ISL54000, ISL54001, and ISL54002 devices. BTL Speaker Amplifiers The ISL54000, ISL54001, and ISL54002 contain two bridge-tied load (BTL) amplifiers designed to drive a speaker load differentially. The output from one BTL is OUTL+ and OUTL-. The output of the other BTL is OUTR+ and OUTR-. A single BTL driver consists of inverting and non-inverting power op amps. The AC signal out of each op amp are equal in magnitude but 180° out-of-phase, so the AC signal at OUTL+ and OUTL- have the same amplitude but are 180° out-of-phase. The same is true of OUTR+ and OUTR-. The speaker load gets connected between the + terminal and - terminal outputs. Driving the load differentially using a BTL configuration doubles the output voltage across the speaker load and quadruples the power to the load. In effect you get a gain of two due to this configuration at the load as compared to driving the load with a single-ended amplifier with its load connected between a single amplifier’s output and ground. The outputs of each BTL are biased at VDD/2. When the load gets connected across the + and - terminal of the BTL, the mid supply DC bias voltage at each output gets cancelled out eliminating the need for large bulky output coupling capacitors. Low Power Shutdown With a logic “1” at the SD control pin the device enters the low power shutdown state. When in shutdown the output amplifiers go into an high impedance state and supply current is reduced to 26µA (typ). In shutdown mode before the amplifiers enter the high impedance/low current drive state, the bias voltage of VDD/2 remains connected at the output through a 100k Ω resistor. This resistor is not present during active operation of the drivers but gets switched in when the SD pin goes high and disconnected when the SD pin goes low. Leaving the DC bias voltage connected through this 100k Ω resistor reduces the transient that is generated across the speaker, while going into or out of shutdown, to a level that does not produce clicking or popping in the speaker. QFN Thermal Pad Considerations The QFN package features an exposed thermal pad on its underside. This pad lowers the package’s thermal resistance by providing a direct heat conduction path from the die to the PCB. Connect the exposed thermal pad to GND by using a (EQ. 1) C 1 6.28 f 100k Ω • • ⁄ ≥ ISL54000, ISL54001, ISL54002 |
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