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ISL54004IRTZ Datasheet(PDF) 7 Page - Intersil Corporation |
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ISL54004IRTZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 13 page 7 FN6513.2 October 30, 2007 The “Typical Application Circuit and Block Diagram” for this device is provided on page 6. The “Truth Table” for the device is provided on page 2. DC Bias Voltage The ISL54004 has 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 100k Ω is the impedance looking into the input of the ISL54004 device. BTL Speaker Amplifier The ISL54004 contains one bridge-tied load (BTL) amplifier designed to drive an 8 Ω speaker load differentially. The output to the BTL amplifier are SPK+ and SPK-. The speaker load gets connected across these terminals. A single BTL driver consists of an 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 SPK+ and SPK- have the same amplitude but are 180° out-of-phase. 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 GND. The outputs of the 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. Headphone (Single-Ended) Amplifiers The ISL54004 contains two single-ended (SE) headphone amplifiers for driving the left and right channels of a 32 Ω or 16 Ω headphone speakers. One SE amplifier drives the right speaker of the headphone and other SE amplifier drives the left speaker of the headphone. The speaker load gets connected between the output of the amplifier and ground. The audio signal at the output of each SE driver is biased at VDD/2 and unlike the BTL driver that cancels this offset due to its differential connection, a capacitor is required at the output of each SE drivers to remove this DC voltage from the headphone load. This coupling capacitor along with the resistance of the speaker load creates a high pass filter that sets the amplifier’s lower bandpass frequency limit. The value of this AC coupling capacitor depends on the low frequency range required for the application. The formula required to calculate the capacitor value is shown in Equation 2: For an application driving a 32 Ω headphone with a lower frequency requirement of 150Hz the required capacitor value is shown in Equation 3: Use the closest standard value. Headphone Sense Function With a logic “1” at the HP control pin while the HO control pin is low will activate the headphone drivers and disable the BTL driver. The “ISL54004 Typical Application Circuit and Block Diagram” on page 6 shows the implementation of the headphone control function using a common headphone jack. The HP pin gets connected to the mechanical wiper blade of the headphone jack. Two external resistors are required for proper operation. A 100k Ω pull-up resistor from the HP pin to VDD and a 10k Ω pull-down resistor from the jack’s audio signal pin to GND of the jack signal pin to which the wiper is connected. See “ISL54004 Typical Application Circuit and Block Diagram” on page 6. When no headphone plug is inserted into the jack the voltage at the HP pin gets set at a low voltage level due to the 10k Ω resistor and 100kΩ resistor divider network connection to VDD. When a headphone is inserted into the jack the 10k Ω resistor gets disconnected from the HP control pin and the HP pin gets pulled up to VDD. Since the HP pin is now high the headphone drivers are activated. A microprocessor or a switch can be used to drive the HP pin rather than using the headphone jack contact pin. Note: With a logic “1” at the HO pin the BTL driver remains active regardless of the voltage level at the HD pin. This allows a headphone to be plugged into the headphone jack without activating the HP drivers. Music will continue to play through the internal 8 Ω speaker rather than the headphones. C 1 6.28 () f () 100k () [] ----------------------------------------------- ≥ (EQ. 1) C 1 6.28 () f () Rspeaker () [] -------------------------------------------------------------- ≥ (EQ. 2) C 1 6.28 () 150 () 32 () [] ------------------------------------------------ ≥ 33 μF = (EQ. 3) ISL54004 |
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