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NJU8753
PRELIMINARY
Analog Signal Input Class D Amplifier with DC-DC Converter for Piezo Speaker
GENERAL DESCRIPTION
The NJU8753 is an analog signal input class D power amplifier with DC-DC converter for Piezo speaker. Input part operates on 2.85V(typ) and a built-in DC-DC converter generates variable output voltage(up to 12V) with input voltage(2.6 to 4.2V). Therefore, it drives Piezo speaker with louder sound and high efficiency. The NJU8753 incorporates BTL amplifier, which eliminate AC coupling capacitors, capable of driving monaural Piezo speaker with simple external LC low-pass filters. Class D operation achieves lower power operation for Piezo speaker, thus the NJU8753 is suited for batterypowered applications.
PACKAGE OUTLINE
NJU8753KN1
FEATURES
Piezo Speaker Driving Output voltage: 8Vrms(Typ.) @VDDO=10.0V 1-channel Analog Signal Input, 1-channel BTL output Standby(Hi-Z), Built-in DC-DC Converter Built-in Low Voltage Detector Built-in Short Protector Operating Voltage :2.6~3.6V(VDD, VREG) :2.6~4.2V(VBAT) CMOS Technology Package Outline :QFN28
PIN CONFIGURATION
28 1
TEST1 TEST3 VREG FB VSS VSS1 VSS1
VDD VSS IIN COM EN1 TEST2 VDDO
VDDO OUTP VSS NC VSS OUTN VDDO
QFN28
Ver.2003-09-26
VOUT VR EN2 NC VDDO
LX LX
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NJU8753
BLOCK DIAGRAM
VDD VSS VREG VOUT LX VR FB EN2
TEST1 TEST2 TEST3
Switching Regulator
VSS1
VDDO IN + COM +
Pulse Width Modulator
OUTP VSS VDDO OUTN VSS
Short Protector
Soft Start
Control
Logic
Low Voltage Detector
EN1
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Ver.2003-09-26
NJU8753 NJU3555
PIN DESCRIPTION
Function Maker test 1 1 TEST1 I This pin must be connected to GND. Maker test 3 2 TEST3 I This pin must be connected to GND. 3 VREG - Switching regulator Power Supply : VREG=2.85V 4 FB I Switching regulator Feedback resistor 5 VSS - Power GND : VSS=0V 6,7 VSS1 - Switching regulator Power GND : VSS1=0V 8,9 LX I Switching regulator voltage input 10 VOUT - Switching regulator Power Supply : Vout=10.0V 11 VR O Switching regulator Output voltage Switching regulator Standby Control 12 EN2 I High : Step-up ON Low : Standby ON This pin must be connected to VREG when step-up ON. 13 NC - Non connection 14, 15 VDDO - Output Power supply 16 OUTN O Negative Output 17 VSS - Power GND : VSS=0V 18 NC - Non connection 19 VSS - Power GND : VSS=0V 20 OUTP O Positive output 21, 22 VDDO - Output Power supply Maker Test 2 23 TEST2 I This pin must be connected to GND. Power Amplifier Standby Control 24 EN1 I High : Standby OFF Low : Standby ON This pin must be connected to VDD when Standby OFF. 25 COM - Analog common 26 IN I Audio Signal Input 27 VSS I Power GND : VSS=0V 28 VDD - Power Supply : VDD=2.85V *Pin No.5(VSS), 6(VSS1), 7(VSS1), 17(VSS), 19(VSS), 27(VSS) should be connected at the nearest point to the IC. *Pin No.14(VDDO) , 15(VDDO), 21(VDDO), 22(VDDO) should be connected at the nearest point to the IC. *Pin No.3(VREG) and 28(VDD) must be connected to VDD, when these pins are not used. No. SYMBOL I/O
Ver.2003-09-26
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NJU8753
FUNCTIONAL DESCRIPTION
(1) Signal Output The OUTP and OUTN generate PWM 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 VDDO, which are the power supply for output drivers. To obtain better THD performance, the stabilization of the power is required. (2) EN1 By setting the EN1 pin to "L", the standby mode is enabled. In the standby mode, the entire functions of the NJU8753 enter a low-power state, and the output pins (OUTP and OUTN) are high impedance. (3) Low Voltage Detector When the power supply voltage drops down to below VDD(MIN), the internal oscillation is halted for prevention to generate unwanted frequency, and the output pins (OUTP, OUTN) become in high impedance. (4) Step-up switching regulator The switching regulator is used as power supply(VDDO) for power amplifier of class-D. The PFM controlled switching regulator works with external components, which are coil, capacitor, Schottky-diode and resistor for Step-up voltage. By setting the EN2 pin to "H", the step-up operation is enabled, and in case of "L", standby mode is enabled. Step-up voltage is set by internal reference voltage(VREG / 2) and external resistors. The step-up voltage can be calculated by the following methods: The step-up voltage is determined by internal reference voltage(VREF), R1 and R2. (See Figure.2) ex. VDD=2.85V, Internal reference voltage(VREF) = VREG / 2=1.425[V], R1=2M, R2=330k " Step-up voltage[V] = VREFx((R1+R2)/R2) = 1.425x((2M + 330k)/330k) = 10.06[V] " Note 1) Apply VREG first, next VBAT. Otherwise, the voltage stress may cause a permanent damage to the IC. (5) Short Circuit Protection The short protector, which protects the NJU8753 against high short-circuit current, turns off the output driver. After about 5 seconds from the protection, the NJU8753 returns to normal operation. The short protector functions at the following accidents. -Short between OUTP and OUTN -Short between OUTP and VSS -Short between OUTN and VSS Note 1) The detectable current and the period for the protection depend on the power supply voltage and ambient temperature. Note 2) The short protector is not effective for a long term short-circuit current but for an instantaneous accident. Continuous high-current may cause permanent damage to the NJU8753.
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Ver.2003-09-26
NJU8753 NJU3555
ABSOLUTE MAXIMUM RATINGS
PARAMETER Supply Voltage LX Input Voltage FB Input Voltage Input Voltage Operating Temperature Storage Temperature Power Dissipation (Ta=25C) SYMBOL RATING UNIT VDD -0.3 ~ +4.0 V VREG -0.3 ~ +4.0 V VDDO -0.3 ~ +15.0 V VLX -0.3 ~ +15.0 V VFB -0.3 ~ +4.0 V Vin -0.3 ~ VDD+0.3 V Topr -40 ~ +85 C Tstg -40 ~ +125 C PD 640* mW * : Mounted on a glass epoxy PCB(50mm x 50mm x 1.6mm).
Note 1) All voltage are relative to "VSS= 0V" reference. Note 2) The LSI must be used inside of the "Absolute maximum ratings". Otherwise, a stress may cause permanent damage to the LSI. Note 3) De-coupling capacitors for VDD(Pin 28)-VSS(Pin 27), VREG(Pin 3)-VSS(Pin 5) and LX(Pin 8,9)-VSS(Pin 17,18,19) should be connected for stable operation.
ELECTRICAL CHARACTERISTIC
(Ta=25C, VDD=VREG=2.85V, VBAT=3.7V, VDDO=10V, VSS=0V, VSS1=0V, TEST1=TEST2=TEST3=0V, EN1=EN2=2.85V, Input Signal=1kHz, Input Signal Level=150mVrms, Frequency Band=20Hz~20kHz, Load Impedance=2.0F 2nd-order 11.5kHz LC Filter(Q=0.72)) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNIT Note VDD 2.6 2.85 3.6 V VDD Supply Voltage VREG 2.6 2.85 3.6 V VREG Supply Voltage VBAT 2.6 3.7 4.2 V VBAT Input Voltage VDDO Supply Voltage VDDO 8.0 10.0 12.0 V Input Impedance ZIN IN pin 20 K Voltage Gain AV 31 dB Input Signal Level THD Output THD 0.05 0.08 % 4 =200mVrms Vo Output THD=10% Maximum Output 8.0 Vrms S/N SN A weight 80 dB 4 Operating Current(Standby) IST EN1=EN2=0V 1 A Operating Current No-load operating ISS 10 15 mA (No signal input) No Signal Input EN1, EN2 pins VIH 0.7VDD VDD V Input Voltage EN1, EN2 pins 0 0.3VDD V VIL EN1, EN2 pins Input Leakage Current ILK 1.0 A Switching regulator fOSC 220 300 380 kHz Oscillating Frequency Switching regulator Step-up Voltage =10.0V 50 mA IOUT VOUT= 10.0V X 95% Maximum Load Current Switching regulator Step-up Voltage =10.0V 100 mV VOUT IOUT =10mA~50mA Load Stability
Ver.2003-09-26
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NJU8753
Note 4) Test system of the output THD and S/N The output THD and S/N are tested in the system shown in Figure 1, where a 2nd-order LC LPF and another filter incorporated in an audio analyzer are used.
Input Signal
NJU8753
2nd-order LC LPF
Filter 20kHz (AES17)
THD Measuring Apparatus
NJU8753 Test Board Figure 1. Output THD and S/N Test System
Audio Analyzer
2nd-order LC LPF Filters
: Refer to "Typical Application Circuit" : 22Hz HPF + 20kHz LPF(AES17) (with the A-Weight filter for S/N and Dynamic-range tests)
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Ver.2003-09-26
NJU8753 NJU3555
TYPICAL APPLICATION CIRCUIT
10F 0.1F 4.7 47H 0.1F 4.7 47uH
VDD
VDD(28) VSS(27)
OUTP(20)
0.1F
Piezo Speaker
2F
OUTN(16) VDD
10F 0.1F
VREG(3) VSS(5)
22H(DCR=0.5)
NJU8753
LX(8,9)
Schottky diode (IF=1A,VF=0.45V)
VBAT
IN
2.4k
2.2F 10F
22000pF
IN(26) COM(25)
VDDO(21,22) VDDO(14,15) VOUT(10)
EN1(24) EN2(12) TEST1(1) TEST2(23) TEST3(2)
VR(11) FB(4) VSS1(6,7) VSS(17,19)
R1
2M
22F 0.1F
R2
330k 10F 0.1F
Figure 2. Application Circuit example
De-coupling capacitors must be connected between each power supply pin and GND. The capacity value should be adjusted on the application circuit and the operation temperature. It may malfunction if capacity value is small. Note 6) The power supply for VDDO require fast driving response performance such as a switching regulator for better THD. THD performance becomes worse by ripple if the capacity of De-coupling capacitors is small. Note 7) The above circuit shows only application example and does not guarantee the any electrical characteristics. Therefore, please test the circuit carefully to fit your application. The cutoff frequency of the LC filter influences the quality of sound. The Q factor of the LC filter must be less than "1". Otherwise, the operating current increase when the frequency of input signal is closed to the cutoff frequency. Note 8) The transition time for EN1 and EN2 signals must be less than 100s. Otherwise, a malfunction may be occurred. Note 9) (1)-(28) indicates pin number.
Note 5)
[CAUTION] The specifications on this databook are only given for information , without any guarantee as regards either mistakes or omissions. The application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights.
Ver.2003-09-26
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