Integrated Depop Circuit with PC Power Supply High Power – 2 W/ch at 5 V, Input 3Ω Load – 800 mW/ch at 3 V, Fully Specified for 3Ω Load, Ultra Low Distortion – 2 W and 3Ω Load Bridged Load (BTL ) or 0.05% THD+N in single-ended (SE) mode, Stereo Input Multiplexer Surface Mount Power Pack 24-pin TSSOP PowerPad Shutdown Co Control...IDD

describe
The TPA0202 is a stereo audio power amplifier in a 24-pin TSSOP thermal package capable of delivering greater than 2 W of continuous rms power per channel into a 3Ω load. The TPA0202 simplifies the design and frees up board space for other functions. A full power distortion level of less than 0.1% THD+N is typical for a 5V supply. Low voltage applications are also well served by the TPA0202, which provides 800 mW per channel into a 3-ohm load from a 3.3 V supply.
The TPA0202 has an integrated Depop circuit that virtually eliminates transients that cause speaker noise during power-up and when using mute and shutdown modes.
The amplifier gain is externally configured via two resistors per input channel, and for settings of 2 to 20 in BTL mode (1 to 10 in SE mode), no external compensation is required. An internal input MUX allows two sets of stereo inputs to the amplifier. In notebook computer applications, the internal speaker is driven as BTL, the line (usually headphone driver) output needs to be SE, and when the SE/BTL input is activated, the TPA0202 automatically switches to SE mode. Driving line outputs up to 700 mW/channel into an external 3-Ω load using the TPA0202 is ideal for small, unpowered external speakers in portable multimedia systems. The TPA0202 also features a shutdown function for power-sensitive applications, keeping the supply current at 5µA. The PowerPad Package† (PWP) provides a level of thermal performance previously only achievable in the TO- 220 model package. Thermal resistances of about 35°C/W are easily achieved in multilayer printed circuit board applications. This enables the TPA0202 to operate at full power into a 3-Ω load at ambient temperatures up to 85°C and forced air cooling of 300 cfm. With an 8Ω load, the operating ambient temperature rises to 100 °C.

Thermal Information The thermally enhanced PWP package is based on the 24-pin TSSOP, but includes a thermal pad to provide efficient thermal contact between the IC and the PWB.
Traditionally, surface mount and power are mutually exclusive terms. Various packages down to 220 size have leads that form gull wings, making them suitable for surface mount applications. However, these packages have only two drawbacks: they do not meet the extremely low requirements (<2 mm) of many of today's advanced systems, nor do they provide a high enough terminal count to accommodate increasing integration. On the other hand, traditional low-power surface mount packages require reduced power consumption, which severely limits the usable range of many high-performance analog circuits.
The PowerPAD package (thermally enhanced TSSOP) combines fine pitch surface mount technology with thermal performance comparable to higher power packages.
The PowerPad software package is designed to optimize heat transfer to the PWB. Due to the very small size and limited mass of the TSSOP package, thermal enhancement is achieved by improving the thermal conduction path to remove heat from the assembly. The thermal pads are formed using a patented lead frame design and fabrication technique to provide direct connection to the heat generating IC. When this pad is soldered or thermally coupled to an external heat sink, high power dissipation in ultra-thin, fine-pitch, surface-mount packages can be reliably achieved.

Application Information Bridge Connection Load with Single-Ended Mode
Linear Audio Power Amplifier (APA) in BTL configuration. The TPA0202 BTL amplifier consists of two linear amplifiers driving across the load. This differential drive configuration has several potential benefits, but the initial consideration is load power. The differential drive of the speakers means that when one side is turned, the other is turned and vice versa. This effectively doubles the voltage swing on the load compared to the ground referenced load. Plugging 2 × vo(pp) into the power equation, where the voltage is squared, yields 4 × the output power from the same supply rail and load impedance (see Equation 1).

The bridge load is configured in a typical computer sound channel operating at 5 volts, and the bridge increases power from a single-ended (SE, ground referenced) limit of 250 mW to an 8 ohm speaker. In terms of sound power, that's a 6dB improvement in how loud it can be heard. In addition to the power increase, there are also frequency response issues. A coupling capacitor is required to prevent the DC offset voltage from reaching the load. These capacitors can be very large (about 33µF to 1000µF), so they tend to be expensive, bulky, occupy valuable PCB area, and have the additional disadvantage of limiting the low frequency performance of the system. This frequency-limiting effect is caused by the high-pass filter network formed by the speaker impedance and coupling capacitor, calculated with Equation 2.

application information

Bridging Connection Loads and Single-Ended Modes (continued)
For example, a 68-microF capacitor with an 8 ohm speaker will attenuate low frequencies below 293 Hz. The BTL configuration eliminates the DC offset, thereby eliminating the need for blocking capacitors. Low frequency performance is limited only by the input network and speaker response. Cost and printed circuit board space are also minimized by eliminating bulky coupling capacitors.

The single-ended configuration and frequency response increase the load power resulting in increased internal power dissipation. Considering that the BTL configuration produces the output power of the 4×SE configuration, the increased power consumption is understandable. The relationship of internal dissipation to output power is discussed further in the Thermal Considerations section.
BTL amplifiers are notoriously efficient, and linear amplifiers are inefficient. The main reason for these inefficiencies is the voltage drop across the output stage transistors. The internal voltage drop has two components. One is the headroom or DC voltage drop that is inversely proportional to the output power. The second component is due to the sinusoidal nature of the output. The total voltage drop can be calculated by subtracting the rms value of the output voltage from VDD. The internal voltage drop is multiplied by the rms value iddrms of the supply current to determine the internal power dissipation of the amplifier.
An easy-to-use formula for calculating efficiency begins with the ratio of power from the source to the load. In order to accurately calculate the rms value of the power in the load and amplifier, one must first understand the current and voltage waveform shapes

Application Information Although the voltage and current of SE and BTL are sinusoidal in the load, the current from the power supply is very different between SE and BTL configurations. In SE applications, the current waveform is a half-wave rectified waveform, while in BTL it is a full-wave rectified waveform. This means that the rms conversion factor is different. Remember that for most waveforms, the push-pull transistors are not turned on at the same time, which supports the fact that each amplifier in a BTL device only draws half the waveform's current from the supply. The following equations are the basis for calculating amplifier efficiency.

Equation 4 was used to calculate the efficiency for four different output power levels. Note that for lower power levels, the amplifier's efficiency is quite low and rises sharply with increasing load power, resulting in nearly flat internal power dissipation over the normal operating range. Note that the internal power dissipation at full output power is less than the power dissipation at half power range. Calculating the efficiency of a specific system is the key to properly designing a power supply. For a stereo 1-W sound system with an 8Ω load and a 5-volt power supply, the maximum power dissipation on the power supply is almost 3.25 W.

Application Information For example, in the calculations in Table 1, if you replace the 5-V supply with a 3.3-V supply (the maximum recommended VDD for the TPA0202 is 5.5 V), the efficiency at 0.5 W will rise from 44% to 67%, 5 The internal power dissipation at V will drop from 0.62 W to 0.25 W. Then, for a stereo 0.5-W system on a 3.3-V supply, the maximum power would be only B. E 1.5 W compared to 2.24 W at 5 V. In other words, use efficiency analysis to select the correct supply voltage and speaker impedance.
Component selection

Schematic of the notebook computer application circuit.

application information

Note: A. This connection is for ultra-low current in shutdown mode. b. A 0.1µF ceramic capacitor should be placed as close to the IC as possible. To filter low frequency noise signals, a 10 microF or larger aluminum electrolytic capacitor should be placed near the audio power amplifier.
TPA0202 full configuration application circuit

Application Information Gain Setting Resistors Rf and Ri The gain of each audio input of the TPA0202 is set by resistors Rf and Ri according to Equation 5 in BTL mode.
BTL gain 2rf ri
BTL mode operation results in a factor of 2 in the gain equation because the inverting amplifier reflects the voltage swing across the load. Considering that the TPA0202 is a MOS amplifier, the input impedance is very high, so although the noise in the circuit increases with the RF value, the input leakage current is usually not a concern. In addition, a range of RF values is required for the amplifier to operate properly for start-up. In conclusion, it is recommended to set the effective impedance seen by the inverting node of the amplifier between 5 kΩ and 20 kΩ. The effective impedance is calculated according to Equation 6.
Effective impedance Rfri Rf Ri
For example, consider an input resistance of 10 kΩ and a feedback resistance of 50 kΩ. The BTL gain of the amplifier is -10, and the effective impedance of the inverting terminal is 8.3 kΩ, which is within the recommended range.
For high performance applications, metal film resistors are recommended as they tend to have lower noise levels than carbon resistors. For RF values above 50 kΩ, the amplifier tends to become unstable due to the electrodes formed by the RF and the inherent input capacitance of the MOS input structure. Therefore, when the RF is greater than 50 kΩ, a small compensation capacitor of about 5 pF should be placed in parallel with the RF. In effect, this creates a low-pass filter network whose cutoff frequency is defined in the formula.
For example, if rf is 100 kΩ and cf is 5 pf, then fc is 318 kHz, well beyond the audio range.

Application Information Input Capacitor ci In a typical application, the input capacitor ci is required to allow the amplifier to bias the input signal to the appropriate DC level for optimum operation. In this case, ci and ri form a high-pass filter, and the corner frequency is determined in Equation 8.
The value of CI is an important factor to consider as it directly affects the bass (low frequency) performance of the circuit. Consider an example where ri is 10 kΩ and the specification calls for a 40 Hz bass response. Equation 8 is reconfigured to Equation 9.
In this example, Ci is 0.40 microF, so a value in the range of 0.47 microF to 1 microF might be chosen. A further consideration for this capacitor is the leakage path of the input source to the load through the input network (Ri, Ci) and the feedback resistor (Rf). This leakage current creates a DC offset voltage at the input of the amplifier, reducing useful headroom, especially in high-gain applications. Therefore, low leakage tantalum or ceramic capacitors are the best choices. When using polarized capacitors, the positive side of the capacitor should face the amplifier input in most applications because the DC level is held at vdd/2, which may be higher than the source DC level. Note that it is important to verify capacitor polarity in the application.
Power Supply Decoupling, the CS TPA0202 is a high performance CMOS audio amplifier that requires sufficient power supply decoupling to ensure that the output Total Harmonic Distortion (THD) is as low as possible. Power supply decoupling also prevents long lead lengths from oscillating between the amplifier and speakers. By using two different types of capacitors, optimal decoupling is achieved for different types of noise on the power leads. For high frequency transients, spikes, or digital spurs on the line, a good low equivalent series resistance (ESR) ceramic capacitor, usually placed as close as possible to 0.1µF of the device, works best with the VDD lead. To filter low frequency noise signals, it is recommended to place a 10 microF or larger aluminum electrolytic capacitor near the audio power amplifier.

Application Information Mid-Rail Bypass Capacitors are the most critical capacitors in Mid-Rail Bypass Capacitors and serve several important functions. During startup or recovery from shutdown mode, the CB determines the startup rate of the amplifier. The second function is to reduce the noise generated by the coupling of the power supply to the output drive signal. This noise comes from the IF generating circuit inside the amplifier and manifests as PSRR and THD+N degradation. The capacitor is powered by the 100-KΩ supply inside the amplifier. To keep startup popups as low as possible, the relationship shown in Equation 10 should be maintained.
1 Chery RF For example, consider a circuit where cb is 1 microF, ci is 0.22 microF, rf is 50 kΩ, and ri is 10 kΩ. Plugging these values into Equation 10, we get 10 ≤ 75, which fits the rule. For best THD and noise performance, 0.1µF to 1µF bypass capacitors, CB or tantalum low ESR capacitors are recommended.
In Figure 63, the fully functional configuration uses two bypass capacitors. This maximizes the separation of the left and right drive circuits. When the absolute minimum cost and/or component space is required, a bypass capacitor can be used, as shown in Figure 62. In this configuration, terminals 6 and 19 must be connected together.
Loading Considerations Very low impedance loads (below 4Ω) coupled with certain external component choices, board layout and routing may cause system oscillations. Use a single air core inductor in series with the load to eliminate any stray oscillations that may occur. An inductance of about 1 μh has been shown to cancel such oscillations. This amplifier does not require special consideration when using loads of 4Ω and above.
Optimize parking lot operations
Circuitry is included in the TPA0202 to minimize the popping noise heard when powering up and exiting shutdown mode. A popping sound occurs when a voltage step is applied to the speaker. If the feedback resistor and input resistor use high impedance, the input capacitor may drift down from the middle rail during muting and shutdown. High gain amplifiers exacerbate this problem when small increments in voltage are multiplied by gain. Therefore, it is advantageous to use a low gain configuration and limit the size of the gain setting resistors. The time constants of the input coupling capacitor (Ci) and gain setting resistors (Ri and Rf) need to be shorter than the time constant formed by the bypass capacitor (Cb) and the output impedance of the mid-rail generator (nominally 100 kΩ) (see Equation 10 ).
Since the PNP transistor clamps the input node, the effective output impedance of the mid-rail generator is actually greater than 100 kΩ

Bypass-side PNP transistor clamp
The PNP transistor limits the voltage drop across the 50 kΩ resistor by slowly rotating the internal node when powered on. At startup, the Xbypass capacitor is 0. The PNP pulls down the midpoint of the bias circuit, so the capacitor has a lower effective voltage and therefore a slower charge. This manifests as a linear ramp (when the PNP transistor conducts), followed by the expected exponential ramp of an RC circuit.
If the expression in Equation 10 cannot be satisfied, or the application still cannot accept a small amount of POP, external circuitry must be added to cancel the POP heard during power-up and when transitioning from silent or off mode.
When the POP happens normally, by keeping the device in SE mode, the POP cannot be heard through the BTL connected speakers (because the negative output is in high impedance when the amplifier is in SE mode).