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BTL∗1 output type is designed and evaluated on the assumption that it is used with BTL system. If it is used with SE∗2 output, not only that the electrical characteristics described in the datasheet will not be obtained, but also pop noise may occur due to the absence of a built-in pop noise prevention circuit for SE output. That is why this not recommended.
BTL∗1 Abbreviation for Bridged Tied Load, also called Balanced Transformer Less. By bridging the outputs of the two amplifiers and connecting them to the loudspeaker, the output voltage is doubled and the output power is quadrupled compared to the SE output type.
SE∗2 Abbreviation for Single Ended. A method in which a Speaker is connected between the Speaker Amplifier output and GND. Since the Speaker Amplifier output is biased by half (1/2) of the Power Supply Voltage, a coupling capacitor must be placed between the Speaker Amplifier output and the Speaker to prevent DC current from flowing through the Speaker. Since the load resistance of the Speaker is generally low (4~8Ω), a large coupling capacitor of about 1000µF is needed to pass low frequency range.
Class-AB Speaker Amplifiers, also called Linear Amplifiers, are Speaker Amplifiers that amplify the input signal as it is to drive the speaker. Generally, this method has an efficiency of less than 50% and generates a lot of heat. Class-D Speaker Amplifiers, also called Digital Amplifiers, are Speaker Amplifiers that convert (analog) input signals into pulses as output. This method achieves high efficiency and low power consumption by converting the output into PWM∗1 pulses.
PWM∗1 Abbreviation for Pulse Width Modulation. In the case of a class-D Speaker Amplifier, an LPF (low-pass filter) is attached to the output so that the carrier signal is removed and the audio signal can be extracted.
Class-D Speaker Amplifiers have higher efficiency and lower power consumption than that of Class-AB Speaker Amplifiers, resulting in less heat generation. However Class-D Speaker Amplifiers have the disadvantage of requiring more external components because an LC filter is generally inserted at the output terminal to eliminate the carrier frequency of PWM. For small output Speaker Amplifiers of around 2 W, it is recommended to use class-D Speaker Amplifier if low power consumption is important. On the otherhand, if reduction of external components is important then class-AB Speaker Amplifier is recommended. For Speaker Amplifiers with medium or higher output power, such as those with output power exceeding 5 W, the Class-AB Speaker Amplifiers may require a heat sink for heat dissipation, which may not reduce the mounting area. Also, since Class-AB Speaker Amplifiers with a linear drive system have better EMI∗1 characteristics than Class-D amplifiers with a pulse drive system, this point should also be taken into consideration when making a selection.
EMI∗1 Abbreviation for Electro Magnetic Interference. Electromagnetic interference is when radio waves or high-frequency electromagnetic waves affect electronic equipment as noise. EMC is also referred to as Electro Magnetic Susceptibility (EMS), which is the ability not to be disturbed by electromagnetic interference.
BD5465GUL/BD5466GUlL/BD5467GUL/BD5468GUL/BD5469GUL are five products with built-in ALC. Each of them has different ALC method, release time, and output power.
BD5465GUL is a fixed output level type where the output level remains constant even if the power supply voltage changes. BD5466GUL/BD5457GUL/BD5468GUL/BD5469GUL are output-level-supply-voltage tracking type where output level also changes when supply voltage changes.
The Class-AB Speaker Amplifier BD7830NUV and Class-D Speaker Amplifier BD27400GUL are variable gain types. BD7836EFV has four types of gain selection by pin setting.
The BD5632NUX, BD5634NUX, and BD5638NUX are fixed gain types, but the gain can be reduced with an external resistor. The gain setting is calculated by the following formula.
Gain = 20×log｜Rf / (Rs+Ri)｜+6dB(BTL)
The internal resistors Ri are 100kΩ (BD5632NUX), 50kΩ (BD5634NUX), and 25kΩ (BD5638NUX), and the feedback resistor Rf is 100kΩ for each.
For the BD5638NUX, when external resistor Rs = 0Ω, Gain = 18dB.
