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EUA6412 2.6-W Stereo Audio Power Amplifier with Four Selectable Gain Settings
DESCRIPTOIN
The EUA6412 is a stereo audio power amplifier. When driving 1 W into 8- speakers, the EUA6412 has less than 0.8% THD+N across its specified frequency range. Included within this device is integrated depop circuitry that virtually eliminates transients that cause noise in the speakers. Amplifier gain is internally configured and controlled by way of two terminals (GAIN0 and GAIN1). BTL gain settings of 6 dB, 10 dB, 15.6 dB, and 21.6 dB are provided, while SE gain is always configured as 4.1 dB for headphone drive. An internal input MUX allows two sets of stereo inputs to the amplifier .The HP/LINE terminal allows the user to select which MUX input is active, regardless of whether the amplifier is in SE or BTL mode. In notebook applications, where internal speakers are driven as BTL and the line outputs (often headphone drive) are required to be SE, the EUA6412 automatically switches into SE mode when the SE/ BTL input is activated, and this reduces the gain to 4.1 dB. The EUA6412 consumes only 5.2mA of supply current during normal operation.
FEATURES
2.6W per Channel Output Power Into 3- Load Internal Gain Control, Which Eliminates External Gain-Setting Components Input MUX Select Terminal PC-Beep Input Depop Circuitry Integrated Two Input Modes Allowable with Single-Ended or Fully Differential Input Low Supply Current and Shutdown Current Thermal Shutdown Protection TSSOP-24 with Thermal Pad RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
Notebook Computers Multimedia Monitors Digital Radios and Portable TVs
Block Diagram
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Typical Application Circuit
Figure 1. Application circuit using single-ended inputs and input MUX
Figure 2. Application circuit using differential input
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Pin Configurations
Package Type Pin Configurations(Top View)
TSSOP-24 with a Thermal Pad exposure on the bottom of the package
Pin Description
PIN PIN I/O DESCRIPTION
BYPASS GAIN0 GAIN1 GND LHPIN LIN LLINEIN LOUT+ LOUTPC-BEEP
11 2 3 1,12 13,24 6 10 5 4 9 14
I I
Tap to voltage divider for internal mid-supply bias generator Bit 0 of gain control Bit 1 of gain control Ground connection for circuitry. Connected to thermal pad.
I I I O O I
HP/ LINE
PVDD RHPIN RIN RLINEIN ROUT+ ROUT-
17 7,18 20 8 23 21 16
I I I I I O O
SHUTDOWN SE/ BTL VDD
22 15 19
I I I
Left channel headphone input, selected when SE/ BTL is held high. Common left input for fully differential input. AC ground for single-ended inputs. Left channel line input, selected when SE/ BTL is held low. Left channel positive output in BTL mode and positive output in SE mode. Left channel negative output in BTL mode and high-impedance in SE mode. The input for PC Beep mode. PC-BEEP is enabled when a > 1-V (peak-to-peak) square wave is input to PC-BEEP or PCB ENABLE is high. HP/LINE is the input MUX control input. When the HP/LINE terminal is held high, the headphone inputs (LHPIN or RHPIN [6, 20]) are active. When the HP/LINE terminal is held low, the line BTL inputs (LLINEIN or RLINEIN [5, 23]) are active. Power supply for output stage. Right channel headphone input, selected when SE/ BTL is held high Common right input for fully differential input. AC ground for single-ended inputs. Right channel line input, selected when SE/ BTL is held low. Right channel positive output in BTL mode and positive output in SE mode. Right channel negative output in BTL mode and high-impedance in SE mode. When held low, this terminal place the entire device, except PC-BEEP detect circuitry, in shutdown mode. Input and output MUX control. When this terminal is held high, the LHPIN or RHPIN and SE output is selected. When this terminal is held low, the LLINEIN or RLINEIN and BTL output are selected. Analog VDD input supply. This terminal needs to be isolated from PVDD to achieve highest performance.
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Ordering Information
Order Number EUA6412QIR1 Package Type TSSOP 24 Marking xxxx A6412A xxxx A6412A Operating Temperature range -40 C to 85C
EUA6412QIT1
TSSOP 24
-40 C to 85C
EUA6412
1/4
1/4
1/4
1/4
Lead Free Code 1: Lead Free 0: Lead Packing R: Tape& Reel T: Tube Operating temperature range I: Industry Standard Package Type Q: TSSOP
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Absolute Maximum Ratings
Supply voltage, VDD------------------------------------------------------------------------------------------------ 6V Input voltage, VI------------------------------------------------------------------------------ -0.3 V to VDD +0.3 V Operating free-air temperature range, TA--------------------------------------------------------- -40X to 85XC C Operating junction temperature range, TJ ------------------------------------------------------ - -40X to 150X C C Storage temperature range, Tstg------------------------------------------------------------------ -- -65X to 150X C C Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds----------------------------------------- 260X C Thermal Resistance JA (TSSOP) ----------------------------------------------------------------------------------------------- 87.9C/W
Recommended Operating Conditions Min
Supply voltage, VDD High-level input voltage, VIH Low-level input voltage, VIL Operating free-air temperature, TA SE/ BTL SHUTDOWN SE/ BTL SHUTDOWN -40 4.5 4 2 3 0.8 85
Max
5.5
Unit
V V V C
Electrical Characteristics at Specified Free-air Temperature, VDD = 5V, TA = 25C Symbol
VOO
PSRR
Parameter
Output offset voltage (measured differentially) Power supply rejection ratio High-level input current Low-level input current Supply current Supply current, shutdown mode
Conditions
VI =0V, AV =2 V/V VDD= 4 V to 5 V VDD=5.5 V, VI = VDD VDD=5.5 V, VI = 0V BTL mode SE mode
EUA6412 Min. Typ. Max.
30 70 1 1 5.2 3 150 10 5 300
Unit
mV dB A A mA A
IIH IIL
IDD IDD(SD)
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Operating Characteristics, VDD = 5V, TA = 25C, RL = 8, Gain =-2V/V, BTL mode Symbol Parameter Conditions
THD+N=10% THD+N=1% Total harmonic distortion plus noise Maximum output power bandwidth Supply ripple rejection ratio SNR Vn Signal-to-noise ratio Noise output voltage BTL mode C(BYP)=0.47F, f= 20 kHz to 20 kHz SE mode PO=1W, f=20 Hz to 15 kHz THD=5% f =1kHz, C(BYP)=0.47F BTL mode
EUA6412 Min. Typ.
2.6 2.05 0.75%
O
Max.
Unit
PO THD+N BOM
Output power
RL=3
W
15 72 94 50 55
kHz dB dB VRMS
Typical Characteristics (Table of Graphs)
No Item Figure
1 2 3 4 5 6 7 8 9 10 11
THD+N vs. Output Power THD+N vs. Output Frequency THD+N vs. Output Voltage Output Noise Voltage vs Bandwidth Supply Ripple Rejection Ratio vs. Frequency Crosstalk vs. Frequency Shutdown Attenuation Signal to noise ratio vs. Frequency Closed Loop Response Output Power vs. Load Resistance Power Dissipation vs. Output Power
3,6,7,8,10,11,12,15, 16,17,19 4,5,9,13,14,18,20 21 22 23,24 25,26 27 28 29,30,31 32,33 34,35
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Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
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Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
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Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
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Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
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Figure 27
Figure 28
Figure 29
Figure 30
Figure 31
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Figure 32
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Figure 33
Figure 34
Figure 35
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Application Information
Gain Setting The gain of the EUA6412 is set by two input terminals, Gain0 and Gain1.The gains listed in Table 1 are realized by changing the taps on the input resistors inside the amplifier.
Table 1.Gain Setting GAIN0 GAIN1
EUA6412
Input Capacitor, Ci In the typical application an input capacitor, Ci, is required to allow the amplifier to bias the input signal to the proper dc level for optimum operation. In this case, Ci and the input impedance of the amplifier, Zi, from a high-pass filter with the corner frequency determined in equation 2.
fc(highpass)=
SE/ BTL
AV(inv)
ZI
1 -----------------(2) 2 Z C
ii
0 0 1 1 X
0 1 0 1 X
0 0 0 0 1
6dB 10dB 15.6dB 21.6dB 4.1dB
90k 70k 45k 25k
Input Resistance Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest value to over 6 times that value. As a results, if a single capacitor is used in the input high pass filter, the -3 dB or cut off frequency will also change by over 6 times. If an additional resistor is connected from the input pin of the amplifier to ground, as shown in the figure below, the variation of the cut-off frequency will be much reduced.
The value of Ci is important to consider as it directly affects the bass (low frequency) performance of the circuit. Consider the example where Zi is 710k and the specification calls for a flat bass response down to 40Hz. Equation 2 is reconfigured as equation 3. 1 Ci = ----------------------------- (3 ) 2 Z fC
i
In this example, Ci is 5.6nF so one would likely choose a value in the range of 5.6nF to 1F. A further consideration for this capacitor is the leakage path from the input source through the input network (Ci) and the feedback network to the load. This leakage current creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especially in high gain applications. For this reason a low- leakage tantalum or ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most applications as the dc level there is held at VDD/2, which is likely higher than the source dc level. Note that it is important to confirm the capacitor polarity in the application.
The-3dB frequency can be calculated using equation 1:
f-3dB =
1 2 C (R || R ) i
---------------------- (1)
If the filter must be more accurate, the value of the capacitor should be increased while the value of the resistor to ground should be decreased. In addition, the order of the filter could be increased.
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Decoupling Capacitor, (CS)
The EUA6412 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is achieved by using two capacitors of different types that target different types of noise on the power supply leads. (ESR) ceramic capacitor, typically 0.1F placed as close as possible to the device VDD lead, works best. For filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10F or greater placed near the audio power amplifier is recommended.
Bypass Capacitor, (CB)
The main disadvantage, from a performance standpoint, is the load impedances are typically small, which drives the low-frequency corner higher, degrading the bass response. Large values of CC are required to pass low frequencies into the load. Consider the example where a CC of 330F is chosen and loads vary from 3, 4, 8, 32, 10k, to 47k. Table 2 summarizes the frequency response characteristics of each configuration.
Table2. Common Load Impedances vs Low Frequency Output characteristics in SE Mode Lowest CC RL Frequency 3 330F 161Hz 4 330F 120Hz 8 330F 60Hz 32 330F 15Hz 10000 330F 0.05Hz 47000 330F 0.01Hz
The bypass capacitor, CB, is the most critical capacitor and serves several important functions. During start-up or recovery from shutdown mode, CB determines the rate at which the amplifier starts up. The second function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and THD+N. Bypass capacitor, CB, values of 0.47F to 1F ceramic or tantalum low-ESR capacitors are recommended for the best THD and noise performance. Output Coupling Capacitor, (CC) For general signal-supply SE configuration, the output coupling capacitor (CC) is required to block the dc bias at the output of the amplifier thus preventing dc currents in the load. As with the input coupling capacitor, the output coupling capacitor and impedance of the load form a high-pass filter governed by equation 4. fc(high)=
1 2 R C LC
As Table 2 indicates, most of the bass response is attenuated into a 4- load and 8- load is adequate, headphone response is good, and drive into line level inputs (a home stereo for example) is exceptional.
Using Low- ESR Capacitors Low- ESR capacitors are recommended throughout this applications section. A real (as opposed to ideal) capacitor can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance the more the real capacitor behaves like an ideal capacitor.
------------------------ (4)
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Bridged-Tied Load Versus Single-Ended Mode Figure 37 show a Class-AB audio power amplifier (APA) in a BTL configuration. The EUA6412 BTL amplifier consists of two Class-AB amplifiers driving both ends of the load. There are several potential benefits to this differential drive configuration, but initially consider power to the load. The differential drive to the speaker means that as one side is slewing up, the other side is slewing down, and vice versa. This in effect doubles the voltage swing on the load as compared to a ground referenced load. Plugging 2xVO(PP) into the power equation, where voltage is squared, yields 4x the output power from the same supply rail and load impedance(see equation 5)
For example, a 68F capacitor with an 8- speaker would attenuate low frequencies below 293 Hz. The BTL configuration cancels the dc offsets, which eliminates the need for the blocking capacitors. Low-frequency performance is then limited only by the input network and speaker response. Cost and PCB space are also minimized by eliminating the bulky coupling capacitor.
V(rms) =
V O(PP) 22
Power =
V (rms) R
L
2
------(5)
Increasing power to the load does carry a penalty of increased internal power dissipation. The increased dissipation is understandable considering that the BTL configuration produces 4 N the output power of the SE configuration. Internal dissipation versus output power is discussed further in the crest factor and thermal considerations section.
Single-Ended Operation In SE mode the load is driven from the primary amplifier output for each channel (OUT+, terminals 21 and 4 ). The amplifier switches single-ended operation when the SE/ BTL terminal is held high. This puts the negative outputs in a high-impedance state, and reduces the amplifier's gain to 1V/V. Input MUX Operation The input MUX allows two separate inputs to be applied to the amplifier. This allow the designer to choose which input is active independent of the state of the SE/ BTL terminal. When the HP/LINE terminal is held high, the headphone inputs are active. When the HP/LINE terminal is held low, the line BTL inputs are active.
In a typical computer sound channel operating at 5V, bridging raises the power into an 8- speaker from a singled-ended (SE, ground reference) limit of 250 mW to 1W. In sound power that is a 6-dB improvement-- which is loudness that can be heard. In addition to increased power there are frequency response concerns. Consider the single-supply SE configuration shown in Figure 38. A coupling capacitor is required to block the dc offset voltage from reaching the load. These capacitors can be quite large (approximately 33F to 1000F) so they tend to be expensive, heavy, occupy valuable PCB area, and have the additional drawback of limiting low-frequency performance of the system. This frequency limiting effect is due to the high pass filter network created with the speaker impedance and the coupling capacitance and is calculated with equation 6.
1 2 R C LC
fC =
----------------------------------(6)
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SE/BTL Operation The ability of the EUA6412 to easily switch between BTL and SE modes is one of its most important cost saving features. This feature eliminates the requirement for an additional headphone amplifier in applications where internal stereo speakers are driven in BTL mode but external headphone or speakers must be accommodated. Internal to the EUA6412 , two separate amplifiers drive OUT+ and OUT- .The SE/ BTL input (terminal 15) control the operation of the follower amplifier that drives LOUT- and ROUT- (terminals 9 and 16).When SE/ BTL is held low, the amplifier is on and the EUA6412 is in the BTL mode. When SE/ BTL is held high, the OUT- amplifiers are in a high output impedance state, which configures the EUA6412 as an SE driver from LOUT+ and ROUT+ (terminals 4 and 21). IDD is reduced by approximately one-half in SE mode. Control of the SE/ BTL input can be from a logic-level CMOS source or, more typically, from a resistor divider network as shown in Figure 39. PC BEEP Operation The PC BEEP input allows a system beep to be sent directly from a computer through the amplifier to the speakers with few external components. The input is activated automatically. When the PC BEEP input is active, both of the LINEIN and HPIN inputs are deselected and both the left and right channels are driven in BTL mode with the signal from PC BEEP. The gain from the PC BEEP input to the speakers is fixed at 0.3V/V and is independent of the volume setting. When the PC BEEP input is deselected, the amplifier will return to the previous operating mode and volume setting. Furthermore, if the amplifier is in shutdown mode, activating PC BEEP will take the device out of shutdown and output the PC BEEP signal, then return the amplifier to shutdown mode. The preferred input signal is a square wave or pulse train with an amplitude of 1 VPP or greater. When the signal is no longer detected, the amplifier will return to its previous operating mode and volume setting. If it is desired to ac-couple the PC BEEP input, the value of the coupling capacitor should be chosen to satisfy equation 7: 1 C - - - - - - - - (7 ) PCB 2f PCB (100k )
Using a readily available 1/8-in. (3.5mm) stereo headphone jack, the control switch is closed when no plug is inserted. When closed the 100-k /1-k divider pulls the SE/BTL input low. When a plug is inserted, the 1-k resistor is disconnected and the SE/ BTL input is pulled high. When the input goes high, the OUTamplifier is shut down causing the speaker to mute(virtually open-circuits the speaker).The OUT+ amplifier then drives through the output capacitor (CO) into the headphone jack.
The PC BEEP input can also be dc- coupled to avoid using this coupling capacitor. The pin normally sits at midrail when no signal is present. Shutdown Modes The EUA 6412 employs a shutdown mode of operation designed to reduce supply current, IDD, to the absolute minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN input terminal should be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the outputs to mute and the amplifier to enter a low-current state, IDD=150A. SHUTDOWN should never be left unconnected because amplifier operation would be unpredictable.
Table 6 . HP/LINE , SE/ BTL , and Shutdown Function
Inputs
HP/ LINE
SE/ BTL SHUTDOWN
Amplifier State INPUT OUTPUT
X Low Low High High
X Low High Low High
Low High High High High
X Line Line HP HP
Mute BTL SE BTL SE
X= Do not care
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Thermal Pad Considerations The thermal pad must be connected to ground. The package with thermal pad of the EUA6412 requires special attention on thermal design. If the thermal design issues are not properly addressed, the EUA6412 will go into thermal shutdown when driving a heavy load. The thermal pad on the bottom of the EUA6412 should be soldered down to a copper pad on the circuit board. Heat can be conducted away from the thermal pad through the copper plane to ambient. If the copper plane is not on the top surface of the circuit board, 8 to 10 vias of 13 mil or smaller in diameter should be used to thermally couple the thermal pad to the bottom plane. For good thermal conduction, the vias must be plated through and solder filled. The copper plane used to conduct heat away from the thermal pad should be as large as practical. If the ambient temperature is higher than 25J ,a larger copper plane or forced-air cooling will be required to keep the EUA6412 junction temperature below the thermal shutdown temperature (150J ). In higher ambient temperature, higher airflow rate and/or larger copper area will be required to keep the IC out of thermal shutdown.
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Package Information
TSSOP-24 (FD)
SYMBOLS A A1 b D E E1 e L
MILLIMETERS MIN. MAX. 1.20 0.00 0.15 0.19 0.30 7.80 6.20 6.60 4.40 0.65 0.45 0.75
INCHES MIN. 0.000 0.007 0.307 0.244 0.173 0.026 0.018 0.030 0.260 MAX. 0.047 0.006 0.012
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