Tecnico de electronica

NJU8755
PRELIMINARY

Analog Signal Input Stereo Class D Power Amplifier
GENERAL DESCRIPTION The NJU8755 is an analog signal input stereo class D power amplifier. The NJU8755 includes Inversion operatinal amplifier input circuit, PWM modulators, an output-short protector and a low voltage detector. The NJU8755 is configured as a BTL amplifier capable of delivering up to 1.2W/channel circuitdrives speaker without external AC coupling with simple external LC low-pass filters. A BTL configuration eliminates the need for external AC coupling capacitors. Class-D achieves high output-efficiency, which leads to long battery life for battery powered applications, thus the NJU8755 is ideally suited for portable audio, note-PC, etc. FEATURES PACKAGE OUTLINE NJU8755V

PIN CONFIGURATION2-Channel Analog Signal Input 20 1 VDD 2-Channel BTL Outputs :1.2W/channel at 5V into 8Ohms 19 2 INL Standby(Hi-Z), BPZ Control 18 3 TEST Built-in Short Protector 17 4 MUTE Built-in Low Voltage Detector 16 5 VDDL Operating Voltage 2.7 ~ 5.25V OUTLP 6 15 CMOS Technology 7 14 VSSL Package Outline SSOP20 8 13 OUTLN 9 12 VDDL 10 11 VDDL BLOCK DIAGRAM VDD VSS

VSS INR COM STBY VDDR OUTRP VSSR OUTRN VDDRVDDR VDDL

INL

+ +
Pulse Width Modulator

OUTLP VSSL VDDL OUTLN VSSL VDDR
Pulse Width Modulator

COM + + INR -

OUTRP VSSR VDDR OUTRN VSSR
Short Protector

Soft Start

Control

Logic

Low Voltage Detector

MUTE

STBY

TEST

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NJU8755
PIN DESCRIPTION No. 1 2 3 4 5 9 10 6 7 8 11 12 16 13 14 15 SYMBOL VDD INL TEST MUTE VDDL OUTLP VSSL OUTLN VDDR OUTRN VSSR OUTRP I/O− I I I − O − O − O − O FUNCTION Power supply : VDD=5.0V L-channel signal input Maker test This pin must be connected to GND. Mute control L : Mute ON H : Mute OFF L-channel power supply : VDDL=5.0V L-channel positive output L-channel power GND L-channel negative output R-channel power supply : VDDL=5.0V

R-channel negative output R-channel power GND : VSSL=0V R-channel positive output Standbycontrol 17 STBY I L : Standby ON H : Standby OFF 18 COM I Analog common 19 INR I R-channel signal input 20 VSS − Power GND : VSS=0V *The relations of ”VSS= VSSL= VSSR=0V” and “VDD= VDDL=VDDR” must be maintained.

INPUT PINS STRUCTURE(MUTE, STBY, TEST) VDD

Input Terminal VSS

Inside Circuit

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NJU8755 NJU3555
FUNCTIONAL DESCRIPTION (1) Signal Output The OUTLP/LN and OUTRP/RN generaterespectively L-channel and R-channel PMW output signals, which will be converted to analog signal via external 2nd-order or higher LC filter. A switching regulator with a high response against a voltage fluctuation is the best selection for the VDDL and VDDR, which are the power supply for output drivers. To obtain better T.H.D. performance, the stabilization of the power is key. (2) Standby Bysetting the STBY pin to “L”, the standby mode is enabled. In the standby mode, the entire functions of the NJU8755 enter a low-power state, and the output pins(OUTLP/LN and OUTRP/RN) are in high impedance. (3) Mute By setting the MUTE pin to “L”, the Mute function is enabled, and the output pins(OUTLP/LN and OUTRP/RN) output square wave(Duty: 50%). (4) Low Voltage Detector When the power supplyvoltage drops down to below VDD(MIN), the internal oscillation is halted not to generate unwanted frequency, and the output pins(OUTLP/LN and OUTRP/RN) become in high impedance. (5) Short Protection Circuit The short protector, which protects the NJU8755 from high short-circuit current, turns off the output drivers of L-channel and R-channel independently. After about 5 seconds from the protection, theNJU8755 returns to normal operation. The short protector is enabled in response to following accidents. Short between OUTLP and OUTLN Short between OUTLP and VSSL Short between OUTLN and VSSL Short between OUTRP and OUTRN Short between OUTRP and VSSR Short between OUTRN and VSSR Note 1) The detectable current and the period for the protection depend on the power supply voltage and ambient...