SLOS474E August   2005  – March 2016 TPA2005D1-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Operating Characteristics
    7. 7.7 Typical Characteristics
  8. Parameter Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Fully Differential Amplifier
        1. 9.3.1.1 Advantages Of Fully Differential Amplifiers
      2. 9.3.2 Efficiency and Thermal Information
      3. 9.3.3 Eliminating the Output Filter With the TPA2005D1-Q1
        1. 9.3.3.1 Effect On Audio
        2. 9.3.3.2 Traditional Class-D Modulation Scheme
        3. 9.3.3.3 TPA2005D1-Q1 Modulation Scheme
        4. 9.3.3.4 Efficiency: Why You Must Use a Filter With The Traditional Class-D Modulation Scheme
        5. 9.3.3.5 Effects Of Applying a Square Wave Into a Speaker
        6. 9.3.3.6 When to Use an Output Filter
    4. 9.4 Device Functional Modes
      1. 9.4.1 Summing Input Signals With the TPA2005D1-Q1
        1. 9.4.1.1 Summing Two Differential Input Signals
        2. 9.4.1.2 Summing A Differential Input Signal And A Single-Ended Input Signal
        3. 9.4.1.3 Summing Two Single-Ended Input Signals
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 TPA2005D1-Q1 With Differential Input
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Component Selection
          2. 10.2.1.2.2 Input Resistors (RI)
          3. 10.2.1.2.3 Decoupling Capacitor (CS)
        3. 10.2.1.3 Application Curve
      2. 10.2.2 TPA2005D1-Q1 With Differential Input and Input Capacitors
        1. 10.2.2.1 Detailed Design Requirements
          1. 10.2.2.1.1 Input Capacitors (CI)
      3. 10.2.3 TPA2005D1-Q1 With Single-Ended Input
  11. 11Power Supply Recommendations
    1. 11.1 Power Supply Decoupling Capacitors
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Component Location
      2. 12.1.2 Trace Width
      3. 12.1.3 8-Pin QFN (DRB) Layout
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Community Resource
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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発注情報

9 Detailed Description

9.1 Overview

The TPA2005D1-Q1 device is a high-efficiency filter-free Class-D audio amplifier capable of delivering up to 1.4 W into 8-Ω loads with a 5-V power supply. The fully-differential design of this amplifier avoids the usage of bypass capacitors and the improved CMRR eliminates the usage of input-coupling capacitors. This makes the device size a perfect choice for small, space constrained applications as only three external components are required. The advanced modulation used in the TPA2005D1-Q1 PWM output stage eliminates the need for an output filter.

9.2 Functional Block Diagram

TPA2005D1-Q1 funblk_los474.gif

9.3 Feature Description

9.3.1 Fully Differential Amplifier

The TPA2005D1-Q1 device 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 TPA2005D1-Q1 device can still be used with a single-ended input; however, the TPA2005D1-Q1 device should be used with differential inputs when in a noisy environment to ensure maximum noise rejection.

9.3.1.1 Advantages Of Fully Differential Amplifiers

Fully differential amplifiers have the following advantages:

  • Input-coupling capacitors not required:
    • The fully differential amplifier allows the inputs to be biased at a voltage other than mid-supply. For example, if a codec has a mid-supply lower than the mid-supply of the TPA2005D1-Q1 device, the common-mode feedback circuit adjusts, and the TPA2005D1-Q1 outputs still is biased at mid-supply of the TPA2005D1-Q1 device. The inputs of the TPA2005D1-Q1 device can be biased from 0.5 V to VDD – 0.8 V. If the inputs are biased outside of that range, input-coupling capacitors are required.
  • Mid-supply bypass capacitor, C(BYPASS), not required:
    • The fully differential amplifier does not require a bypass capacitor. This is because any shift in the mid-supply affects both positive and negative channels equally and cancels at the differential output.
  • Better RF immunity:
    • The fully differential amplifier cancels noise from RF interference much better than the typical audio amplifier.

9.3.2 Efficiency and Thermal Information

As an example, the DRB package has a RθJA of 49.5°C/W, the maximum allowable junction temperature of 150°C, and a maximum internal dissipation of 0.2 W (worst case 5-V supply and 8-Ω load). Use Equation 1 to calculate the maximum ambient temperature.

Equation 1. TAMax = TJMax – RθJAPDmax = 150 – 49.5(0.2) = 140.1°C

Equation 1 shows that the calculated maximum ambient temperature is 140.1°C at maximum power dissipation with a 5-V supply; however, the maximum ambient temperature of the package is limited to 85°C (note that the TPA2005D1TDGNRQ1 supports up to 105°C). Because of the efficiency of the TPA2005D1-Q1, it can operate under all conditions to an ambient temperature of 85°C. The TPA2005D1-Q1 is designed with thermal protection that turns the device off when the junction temperature surpasses 150°C to prevent damage to the IC. Also, using speakers more resistive than 8 Ω dramatically increases the thermal performance by reducing the output current and increasing the efficiency of the amplifier.

9.3.3 Eliminating the Output Filter With the TPA2005D1-Q1

This section focuses on why the user can eliminate the output filter with the TPA2005D1-Q1.

9.3.3.1 Effect On Audio

The class-D amplifier outputs a pulse-width modulated (PWM) square wave, which is the sum of the switching waveform and the amplified input audio signal. The human ear acts as a band-pass filter such that only the frequencies between approximately 20 Hz and 20 kHz are passed. The switching frequency components are much greater than 20 kHz, so the only signal heard is the amplified input audio signal.

9.3.3.2 Traditional Class-D Modulation Scheme

The traditional class-D modulation scheme has a differential output in which each output is 180 degrees out of phase and changes from ground to the supply voltage, VDD. Therefore, the differential pre-filtered output varies between positive and negative VDD, where filtered 50% duty cycle yields 0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown in Figure 31. Note that, even at an average of 0 V across the load (50% duty cycle), the current to the load is high, causing a high loss and thus causing a high supply current.

TPA2005D1-Q1 ai_ClassD_los474.gif Figure 31. Traditional Class-D Modulation Scheme Output Voltage and Current Waveforms Into an Inductive Load With No Input

9.3.3.3 TPA2005D1-Q1 Modulation Scheme

The TPA2005D1-Q1 device uses a modulation scheme that still has each output switching from 0 to the supply voltage. However, OUT+ and OUT– are now in phase with each other, with no input. The duty cycle of OUT+ is greater than 50% and OUT– is less than 50% for positive voltages. The duty cycle of OUT+ is less than 50% and OUT– is greater than 50% for negative voltages. The voltage across the load remains at 0 V throughout most of the switching period, greatly reducing the switching current, which reduces any I2R losses in the load.

TPA2005D1-Q1 ai_IndLoad_los474.gif Figure 32. TPA2005D1-Q1 Output Voltage and Current Waveforms Into an Inductive Load

9.3.3.4 Efficiency: Why You Must Use a Filter With The Traditional Class-D Modulation Scheme

The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform results in maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current is large for the traditional modulation scheme because the ripple current is proportional to voltage multiplied by the time at that voltage. The differential voltage swing is 2 × VDD, and the time at each voltage is one-half the period for the traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half-cycle for the next half-cycle, while any resistance causes power dissipation. The speaker is both resistive and reactive, whereas an LC filter is almost purely reactive.

The TPA2005D1-Q1 modulation scheme has very little loss in the load without a filter because the pulses are very short and the change in voltage is VDD instead of 2 × VDD. As the output power increases, the pulses widen, making the ripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for most applications the filter is not needed.

An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flow through the filter instead of the load. The filter has less resistance than the speaker, resulting in less power dissipation, which increases efficiency.

9.3.3.5 Effects Of Applying a Square Wave Into a Speaker

If the amplitude of a square wave is high enough and the frequency of the square wave is within the bandwidth of the speaker, a square wave could cause the voice coil to jump out of the air gap, scar the voice coil, or both. A 250-kHz switching frequency, however, is not significant because the speaker cone movement is proportional to 1/f2 for frequencies beyond the audio band. Therefore, the amount of cone movement at the switching frequency is very small. However, damage could occur to the speaker if the voice coil is not designed to handle the additional power. To size the speaker for added power, the ripple current dissipated in the load must be calculated by subtracting the theoretical supplied power, PSUP THEORETICAL, from the actual supply power, PSUP, at maximum output power, POUT. The switching power dissipated in the speaker is the inverse of the measured efficiency, ηMEASURED, minus the theoretical efficiency, ηTHEORETICAL.

Equation 2. TPA2005D1-Q1 Q19_PSPKR_los474.gif
Equation 3. TPA2005D1-Q1 Q20_PSPKR1_los474.gif
Equation 4. TPA2005D1-Q1 Q21_PSPKR2_los474.gif
Equation 5. TPA2005D1-Q1 Q22_Theort_los474.gif

The maximum efficiency of the TPA2005D1-Q1 device with a 3.6-V supply and an 8-Ω load is 86% from Equation 5. Using Equation 4 with the efficiency at maximum power (84%). An additional 17 mW is dissipated in the speaker. The added power dissipated in the speaker is not an issue as long as it is taken into account when choosing the speaker.

9.3.3.6 When to Use an Output Filter

Design the TPA2005D1-Q1 device without an output filter if the traces from amplifier to speaker are short. The TPA2005D1-Q1device passed FCC and CE radiated emissions with no shielding and with speaker trace wires 100 mm long or less.

A ferrite bead filter often can be used if the design is failing radiated emissions without an LC filter, and the frequency-sensitive circuit is greater than 1 MHz. If choosing a ferrite bead, choose one with high impedance at high frequencies, but very low impedance at low frequencies.

Use an LC output filter if there are low-frequency (<1 MHz) EMI-sensitive circuits and/or there are long leads from amplifier to speaker.

Figure 33 and Figure 34 show typical ferrite bead and LC output filters.

TPA2005D1-Q1 ai_NECTokin_los474.gif Figure 33. Typical Ferrite Chip Bead Filter (Chip Bead Example: NEC/Tokin: N2012ZPS121)
TPA2005D1-Q1 ai_LCout_los474.gif Figure 34. Typical LC Output Filter, Cutoff Frequency of 27 kHz

9.4 Device Functional Modes

9.4.1 Summing Input Signals With the TPA2005D1-Q1

The TPA2005D1-Q1 device makes it easy to sum signal sources or use separate signal sources with different gains. This allows one speaker to be connected to the TPA2005D1-Q1 device with multiple input sources. It can also be used to output a stereo signal to a mono speaker by summing the left and right channels.

9.4.1.1 Summing Two Differential Input Signals

Two extra resistors are required for summing differential signals (a total of 5 components). The gain for each input source can be set independently (see Equation 6 and Equation 7 and Figure 35).

Equation 6. TPA2005D1-Q1 Q4_gain1_los474.gif
Equation 7. TPA2005D1-Q1 Q5_gain2_los474.gif

If summing left and right inputs with a gain of 1 V/V, use RI1= RI2= 300 kΩ.

TPA2005D1-Q1 ai_TwoDif_los474.gif Figure 35. Application Schematic With TPA2005D1-Q1 Summing Two Differential Inputs

9.4.1.2 Summing A Differential Input Signal And A Single-Ended Input Signal

Figure 36 shows how to sum a differential input signal and a single-ended input signal. Ground noise can couple in through IN+ with this method. It is better to use differential inputs. The corner frequency of the single-ended input is set by CI2, shown in Equation 10. To ensure that each input is balanced, the single-ended input must be driven by a low-impedance source even if the input is not in use.

Equation 8. TPA2005D1-Q1 Q4_gain1_los474.gif
Equation 9. TPA2005D1-Q1 Q5_gain2_los474.gif
Equation 10. TPA2005D1-Q1 Q8_CI2_los474.gif

The high-pass corner frequency of the single-ended input is set by CI2. If the desired corner frequency is less than 20 Hz, then:

Equation 11. TPA2005D1-Q1 Q9_CI2a_los474.gif
Equation 12. TPA2005D1-Q1 Q10_CI2b_los474.gif
TPA2005D1-Q1 ai_DiffSing_los474.gif Figure 36. Application Schematic With TPA2005D1-Q1 Summing Differential Input And
Single-Ended Input Signals

9.4.1.3 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 Equation 13 through Equation 16 and Figure 37). 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.

Equation 13. TPA2005D1-Q1 Q4_gain1_los474.gif
Equation 14. TPA2005D1-Q1 Q5_gain2_los474.gif
Equation 15. TPA2005D1-Q1 Q13_CI1_los474.gif
Equation 16. TPA2005D1-Q1 Q8_CI2_los474.gif
Equation 17. TPA2005D1-Q1 Q15_CP_los474.gif
Equation 18. TPA2005D1-Q1 Q16_RP_los474.gif
TPA2005D1-Q1 ai_TwoSingE_los474.gif Figure 37. Application Schematic With TPA2005D1-Q1 Summing Two Single-Ended Inputs