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PDF NJU8761 Data sheet ( Hoja de datos )
| Número de pieza | NJU8761 | |
| Descripción | Analog | |
| Fabricantes | JRC | |
| Logotipo |  |
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NJU8761
www.DataSheet4U.com
PRELIMINARY
Analog Signal Input Monaural Class-D Power Amplifier
for Piezo Speaker
GENERAL DESCRIPTION
The NJU8761 is an analog signal input monaural
class-D amplifier for Piezo speaker.
The NJU8761 incorporates BTL amplifiers, which
eliminate AC coupling capacitor. The input block
operates on 2.6V(Min.) as power supply and the
output block operates up to 12V, therefore it can output
close to 17.5VP-P amplified signal and drive Piezo
speaker with louder sound and high efficiency.
Class-D operation achieves lower power operation
for Piezo speaker, thus the NJU8761 is suited for
battery-powered applications such as cellular phone
and PDA.
PACKAGE OUTLINE
NJU8761KM1
FEATURES
Piezo Speaker Driving
Output voltage 6.2 Vrms (Typ.) @VDDO=10 V, THD+N=10%
Analog input, Monaural BTL output
Standby(Hi-Z), Mute control
Built-in Low Voltage Detector for VDD & VDDO
Operating Voltage Input Block: 2.6~3.6V(VDD)
Output Block: 8.0~12.0V(VDDO)
CMOS Technology
Package Outline QFN20-M1
PIN CONFIGURATION
20
1
BOOST
NFIN
IN
VSS
COM
5
6
16
15
NC
TEST
TEST
TEST
STBYB
11
10
Ver.2006-06-19
-1-
1 page  
www.DataSheet4U.com
NJU38575651
(6) Power Amplifier
(6-1) Input signal
The amount of current passing through a capacitive load increases proportionately with frequency of audio signal.
Input filters should be put in the input line to reduce load current at high frequency-band.
The input filters are composed of 1st-order RC LPF(Low Pass Filter) and 1st-order RC HPF(High Pass Filter).
fCH1(Cut-off frequency of HPF) and fCL1(Cut-off frequency of LPF) are determined by input resistance(RIN), resistor
for LPF(RLPF), capacitor for LPF(CLPF) and AC coupling capacitor(CC).
When RIN=10kΩ, RLPF=3kΩ and CLPF=0.01µF, CC=2.2µF, fCH1 and fCL1 are roughly calculated
as following expressions.
f CH1
=
2π (RIN
1
+ RLPF )CC
=
2 × 3.14×
(10 ×103
1
+ 3×103
)×
2.2 ×10-6
≅ 5.6[Hz]
f CL1
=
2π
(RIN
1
// RLPF
)CLPF
=
2 × 3.14× (10 ×103
1
// 3×103 ) × 0.01×10-6
≅ 6.9[kHz]
(6-2) Output signal
The output signals are PWM signals, which will be converted to analog signal via external 2nd-order or higher LC
filter. To reduce the current consumption with signal-input close to cutoff-frequency of LPF(fc). Damping resistor
should be connected between OUTP pin and coil, and between OUTN pin and coil.
Note 6) Q(The gain of LPF at fc) should be within 1 with settings of L, C and RDAMP.
When L=22µF, CL=1.1µF, RDAMP=4.3Ω and equivalent series resistance(RDCR)=0.21Ω, cut-off frequency of LPF(fc)
and Q are roughly calculated as following expressions.
fc = 1 = 1 ≅ 23[kHz]
2π 2LCL 2 × 3.14× 2 × 22 ×10-6 ×1.1×10-6
( )Q = 1
RDAMP + RDCR
L
2C L
= (4.3 +10.21)×
22 ×10-6
2 ×1.1×10-6
≅ 0.70
(6-3) Voltage gain
The voltage gain is estimated by multiplying the voltage gain of input amplifier by the gain of PWM circuit and the
gain of BTL output stages. The gain of PWM circuit is 2.8 times and the gain of BTL output stage is twofold. The
voltage gain of input amplifier is determined by the ratio of negative feedback resistor (RFB connected with NFIN
pin) versus external input resistor (RIN connected with IN pin).
Note 7) The negative feedback resistor (RFB) must be set 10kΩ or further. In addition, due to the limitation of
phase-margin, the gain of input amplifier must be one time or further.
When input resistor is 10kΩ and negative feedback resistor is 39kΩ, total voltage gain is roughly calculated as
following.
Voltage gain = 39kΩ / 10kΩ x 2.8 x 2 = 21.8 times ≅ 26dB
Note 8) The maximum output amplitude is approx ”VDDx0.7 [VPP]”. When the gain of input amplifier is one time,
maximum input amplitude is ”VDDx0.7 / 1 [VPP]”. If input signal exceeds maximum input amplitude, output
waveform must be distorted.
(6-4) Oscillation frequency
The oscillation frequency is determined by ROSC (connected with ROSC pin), COSC (connected with COSC pin) and
power supply (VDD).
Note 9) 250kHz ± 20kHz is recommended for oscillation frequency. The following conditions would be suitable at
this frequency. (VDD is 2.85V, ROSC is 180kΩ and COSC is 390pF)
f OSC
=
3.3×VDD + 8.5
COSC × ROSC
=
3.3× 2.85 + 8.5
390 ×10-12 ×180 ×103
≅
255[kHz]
Ver.2006-04-04
-5-
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet NJU8761.PDF ] | |
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