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SC7422
2-CH AUDIO POWER AMPLIFIER
DESCRIPTION
The SC7422 is a class AB power amplifier which designed for dual audio purpose. It can deliver 2W x 2 power output to the 4 load in the
SOP-16-375-1.27
2W x 2
5V operation voltage. Total harmonic distortion is lower than 0.03%. The output mode can be switched between the SE and BTL mode. The volume also can be changed by a 32 steps volume controller. Moreover, the SC7422 requires a few extra components in the application. It is suitable for small or portable products.
FEATURES
* Operation voltage : 5V * Output power : 2Wx2(RL=4 ) * Low harmonics distortion (THD=0.03%) * 32 steps volume control with 1.5dB per step from -45dB to 0dB * Two output modes (SE and BTL) switched * Low quiescent operation current * No POPO noise when turn on/off * Standby function, Low standby current(Is<0.7 A) * Thermally protected
DIP-16-300-2.54
ORDERING INFORMATION
Device SC7422 SC7422S Package DIP-16-300-2.54 SOP-16-375-1.27
APPLICATIONS
* LCD Monitors for TV * Portable audio * Multimedia audio * Other audio applications
BLOCK DIAGRAM
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SC7422
ABSOLUTE MAXIMUM RATING
Characteristics Supply Voltage Maximum Input Voltage For Any Pin Maximum Input Current For Each Input Pin (*) Operating Ambient Temperature Storage Temperature Thermal Ambient Thermal Resistance From Junction To Case can be avoided. (**) Ambient Temperature: Tamb=25C. Resistance From Junction To Symbol VCC Vin(max) Iin(max) Tamb Tstg
JA JC
Rating 0 ~7 -0.3 ~ VCC +0.3 -10 ~+10 -40 ~+85 -65 ~+150 88.8 (**) 26 (**)
Unit V V mA C C C/W C/W
(*) Maximum instantaneous input current for any pin must be less than 100mA, so that the CMOS latch-up effect
ELECTRICAL CHARACTERISTICS
(Refer to the test circuit, VCC=5V; f=22Hz~22KHz; Tamb=25C, unless otherwise specified.) Characteristics Supply Voltage Quiescent Operation Current Symbol VCC BTL Is SE Shutdown = ON THD=1%, RL=8 BTL Output Power Po SE Total Harmonic Distortion BTL SE Vatt Vstep Mute CB CS SNR Vno THD=10%, RL=8 THD=1%, RL=4 THD=10%, RL=4 THD=1%, RL=32 THD=10%, RL=32 Po=0.2W, RL=4 Po=1W, RL=4 Po=50mW, RL=32 Test conditions Min. 3 8 6 0.2 1.0 1.2 1.4 1.8 80 100 0.03 0.06 0.03 -1 -44 1.3 -85 -1 85 77 85 25 Typ. 5 10 8 0.7 1.1 1.4 1.6 2.0 85 110 0.05 0.08 0.05 0 -45 1.5 -88 0 88 80 90 40 Max. 6 14 12 1 1.1 1.6 1.8 2.1 90 120 0.07 0.15 0.07 +1 -46 1.7 -90 +1 91 83 91 50 mW % % % dB dB dB dB dB dB V W Unit V mA mA A
THD
Volume Control Range Volume Control Step Mute Channel Balance Channel Separate Signal-to-Noise Ratio Output Noise Voltage
DC Vol = 5V, F = 1kHz DC Vol = 17%Vcc Vatt = 0 ~ -45dB DC Vol = 0V Rin = Rf = 20k BTL SE F=1kHz
(To be continued)
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SC7422
(Continued) Characteristics Output Offset Voltage Supply Rejection Thermally protected Input Voltage For Shutdown Pin Input Voltage For SE/BTL Pin Voltage Ripple Symbol Voff SVRR TH VSD VSB Test conditions DC Vol = 0V From +OUT to -OUT BTL SE F=1kHz Min. 25 58 52 50% 80% Typ. 50 60 55 120 80 20% 60% 10% 90% 20% Max. 100 63 58 30% Unit mV dB C Vcc Vcc
Overheat to shutdown Return to normal operation Shutdown = OFF Shutdown = ON BTL SE Vcc=3~5V Vcc=3~5V
PIN CONFIGURATION
PIN DESCRIPTION
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 Pin Name Shutdown VCC DC Vol VO1 VIN1 VIN2 VO2 GND +OUT2 VCC -OUT2 SE/BTL I/O I -I I I I I -O -O I Supply Volume control Buffer output of channel 1 Signal input of channel 1 Signal input of channel 2 Buffer output of channel 2 Ground Non inverted loudspeaker output of channel 2 Supply Inverted loudspeaker output of channel 2 Output mode control. When this pin is logic high, SE mode is selected. When it is logic low, BTL mode is selected. (To be continued) Pin Description Stand-by control, logic high active
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SC7422
(Continued) Pin No. 13 14 15 16 Pin Name Bypass -OUT1 VCC +OUT1 I/O O O -O Pin Description Half supply voltage ripple rejection Inverted loudspeaker output of channel 1 Supply Non inverted loudspeaker output of channel 1
FUNCTION DESCRIPTION
Gain Setting for Input Stage The gain for each audio input stage of the SC7422 is set by external resistors R1 and R2 (see typical application circuit). It is recommended that R1 = R2 = 20k in the application and the gain is 0dB. If the amplitude of audio input voltage is lower, for example, the peak-peak value is less than 2Vpp, it should be improve the gain, whereas, it should be reduce the gain. However, the amplitude of audio input voltage is so high that the output wave would be distortion. Therefore, the amplitude of audio signal source should be checked at first. And the gain in the application should be set following Table 1. Table 1 Gain Setting for Input Stage Operation Voltage The peakpeak value of input voltage VIN <1.25Vpp VCC=3V VIN <2.5Vpp VIN <5Vpp Gain Setting for Input Stage +6dB 0dB -6dB VCC=5V Operation Voltage The peakpeak value of input voltage VIN <2Vpp VIN <4Vpp VIN <8Vpp Gain Setting for Input Stage +6dB 0dB -6dB
Otherwise, the minimum value of input resistor R1 is 10k, in order to ensure proper impedance for input. 32 Steps Volume Control The SC7422 includes a 32 steps volume controller. It changes the volume gain linearly with 1.5dB per step from -45dB to 0dB. The volume is controlled by input voltage of DC Vol pin. As the voltage was increasing, the volume is louder. Table 2 shows the relationship of them. Table 2 32 Steps Volume Setting Step 1 2 3 4 5 Volume (dB) 0 -1.5 -3 -4.5 -6 DC Vol VH(%) Vcc 64.4 63.0 61.4 59.8 DC Vol VL(%) 64.2 62.8 61.2 59.4 57.6 Step 17 18 19 20 21 Volume (dB) -24 -25.5 -27 -28.5 -30 DC Vol VH(%) 38.1 35.6 31.8 29.2 27.6 DC Vol VL(%) 30.4 29.0 27.4 25.4 23.8 (To be continued)
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SC7422
(Continued) Step 6 7 8 9 10 11 12 13 14 15 16 Volume (dB) -7.5 -9 -10.5 -12 -13.5 -15 -16.5 -18 -19.5 -21 -22.5 DC Vol VH(%) 57.9 56.1 54.1 52.1 49.4 47.5 45.5 44.0 41.8 39.8 38.3 DC Vol VL(%) 56.0 54.0 51.8 48.8 47.4 45.4 43.6 41.6 39.8 37.6 36.6 Step 22 23 24 25 26 27 28 29 30 31 32 Volume (dB) 31.5 -33 -34.5 -36 -37.5 -39 -40.5 -42 -43.5 -45 MUTE DC Vol VH(%) 26.2 24.0 22.5 20.4 18.0 15.1 13.1 10.6 8.8 6.7 4.3 DC Vol VL(%) 21.8 20.0 18.0 14.4 13.0 11.0 9.0 7.2 5.4 3.0 GND
Output Mode Control The output mode of the SC7422 can be switched between the SE (Single-Ended) and BTL (Bridge-Tied Load) mode. It is recommended to apply BTL mode to obtain more output power while driving the loud speaker. SE mode can be set to shutdown some parts of amplifiers while driving the stereo headphone. Therefore, the quiescent operation current is reduced. POPO Noise Suppress When an audio power amplifier with a single supply turns on, the POPO Noise can be heard. The reason is that the output voltage of amplifier would take hundreds of milliseconds to increase from 0V to 1/2 Vcc. This time is controlled by CB, the external capacitor of Bypass pin. As the CB was increasing, the time is longer, so it is much better to suppress POPO noise. However, the charging and discharging time for the input or output capacitors should be less than this time. Therefore, CB is related with the input or output capacitors. The values of these capacitors are recommended in the typical application circuit. Thermally protected There is a thermally protected protection circuit in the SC7422. If the chip temperature is over 120C, the protection circuit will start up to shutdown the output stages of audio power amplifier. The chip will return to the normal operation, until the chip temperature falls to 80C. Power Dissipation and Heat Sinking When the load is a resistor, the maximum of average power dissipation for the SC7422 is calculated as follows: PDISS(MAX) = 2(2Vcc)2 / (22RL) + PQ Where Vcc is the operation voltage, RL is the load resistor, PQ is the static power consumption. PQ=VCCxIs Where Is is the operation current. For example, if the SC7422 drives the 4 dissipation is 2.6W. load in 5V supply, the power
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SC7422
There is the formula of heat sinking for the SC7422:
JA =
(TJ(max) -TA )/ PDISS
Where
JA
is the thermal resistance from junction to ambient, TJ(max) is the junction temperature, TA is ambient
temperature, PDISS is the power dissipation. If the junction temperature remains below 150C but the ambient temperature has reached to 50C, the total junction-to-ambient thermal resistance must be less than
JA = JA
calculated as follows:
(150C - 50C) / 2.6W =38.4C/W. = 12.4C/W
Using JC=26C /W, the heat-sink thermal resistance must be less than:
JA JC
So the SC7422 doesn' need heat sink in the normal operation. In application, the copper foil which connects t GND on PCB can be utilized for heat sinking to maintain proper operation temperature.
TYPICAL APPLICATION CIRCUIT
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SC7422
PACKAGE OUTLINE
DIP-16-300-2.54
Unit: mm
SOP-16-375-1.27
Unit: mm
10.300.20
7.500.20
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0.200.10
2.500.20
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0.700.10
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SC7422
HANDLING MOS DEVICES:
Electrostatic charges can exist in many things. All of our MOS devices are internally protected against electrostatic discharge but they can be damaged if the following precautions are not taken: * Persons at a work bench should be earthed via a wrist strap. * Equipment cases should be earthed. * All tools used during assembly, including soldering tools and solder baths, must be earthed. * MOS devices should be packed for dispatch in antistatic/conductive containers.
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