NJU8755
-1-
Ver.2008-11-19
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
operational amplifier input circuit, PWM modulators, an
output-short protector and a low voltage detector. The
NJU8755 incorporates BTL amplifiers, which eliminate
AC coupling capacitors, capable of driving up to
1.2W/channel with simple external LC low-pass filters.
Class-D operation achieves high power-efficiency,
which achieves longer battery life for battery powered
applications, thus the NJU8755 is suited for portable
audio, note-PC, etc.
FEATURES
2-Channel Analog Signal Input
2-Channel BTL Outputs :1.2W/channel at 5V into 8Ω
Standby(Hi-Z), Mute Control
Built-in Short Protector
Built-in Low Voltage Detector
Operating Voltage 2.7 to 5.25V
CMOS Technology
Package Outline SSOP20
BLOCK DIAGRAM
VDD
INL
TEST
MUTE
VDDL
VSS
INR
COM
STBY
VDDR
1
2
3
4
5
20
19
18
17
16
6
7
15
14
OUTLP
VSSL
OUTRP
VSSR
OUTLN 8
9
10
VDDL
VDDL
OUTRN
13
12
11
VDDR
VDDR
Short
Protector
VDD
Control Logic Low Voltage
Detecto
r
Soft Start
VSS
MUTE STBY TEST
Pulse
Width
Modulator
+
-
+
-
COM
VDDL
OUTLP
VSSL
VDDL
OUTLN
VSSL
+
-
+
-
Pulse
Width
Modulator
INL
INR
VDDR
OUTRP
VSSR
VDDR
OUTRN
VSSR
PIN CONFIGURATION
PACKAGE OUTLINE
NJU8755V
NJU8755
- 2 - Ver.2008-11-19
PIN DESCRIPTION
No. SYMBOL I/O FUNCTION
1 VDD − Power Supply : VDD=5.0V
2 INL I L-channel signal input
3 TEST I
Maker test
This pin must be connected to GND.
4 MUTE I
Mute control
Low : Mute ON High : Mute OFF
5
9
10
VDDL − L-channel Power Supply : VDDL=5.0V
6 OUTLP O L-channel positive output
7 VSSL − L-channel Power GND
8 OUTLN O L-channel negative output
11
12
16
VDDR − R-channel Power Supply : VDDR=5.0V
13 OUTRN O R-channel negative output
14 VSSR − R-channel Power GND : VSSR=0V
15 OUTRP O R-channel positive output
17 STBY I
Standby control
Low : Standby ON High : Standby OFF
18 COM − 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.
*Pin No.4(MUTE) and 17(STBY) must be connected to VDD, when these pins are not used.
NJU3555NJU8755
-3-
Ver.2008-11-19
FUNCTIONAL DESCRIPTION
(1) Signal Output
The OUTLP/LN and OUTRP/RN generate respectively L-channel and R-channel 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 VDDL and VDDR, which are the power supply for
output drivers. To obtain better THD performance, the stabilization of the power is required.
(2) Standby
By setting 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 high impedance.
(3) Mute
By setting the MUTE pin to “L”, the Mute function is enabled. In the Mute mode, the output pins(OUTLP/LN and
OUTRP/RN) output square wave(Duty: 50%).
(4) 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(OUTLP/LN and OUTRP/RN) become in high impedance.
(5) Short Circuit Protection
The short protector, which protects the NJU8755 against high short-circuit current, turns off the output drivers
of L-channel and R-channel independently. After about 5 seconds from the protection, the NJU8755 returns to
normal operation. The short protector functions at 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 temperature.
Note 2) The short protector is not effective for a long term short-circuit but for an instantaneous accident.
Continuous high-current may cause permanent damage to NJU8755.
NJU8755
- 4 - Ver.2008-11-19
ABSOLUTE MAXIMUM RATINGS
(Ta=25°C)
PARAMETER SYMBOL RATING UNIT
Supply Voltage
VDD
VDDL
VDDR
-0.3 ~ +5.5
-0.3 ~ +5.5
-0.3 ~ +5.5
V
V
V
Input Voltage Vin -0.3 ~ VDD+0.3 V
Operating Temperature Topr -40 ~ +85 °C
Storage Temperature Tstg -40 ~ +125 °C
Power Dissipation PD 300 (SSOP20) mW
Note 1) All voltage are relative to “VSS= VSSL= VSSR=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-VSS, VDDL-VSSL , and VDDR-VSSR should be connected for stable operation.
Note 4) Power Dissipation
The class-D amplifiers are more power efficiency, and dissipate power less than general
analog-amplifiers. In theory, the NJU8755 actualize quite high output-power such as 1.2W/channel at 5V
operation with 8ohms load, and total power is supposed to be 2.4W. For this reason, it looks as if the
NJU8755 exceeds the absolute maximum rating of the power dissipation. However, in practice, the
effective output-power of usual music sound is only about 1/10 of its maximum output power, thus it may
never exceed the absolute maximum rating.
The maximum power dissipation in the system is calculated, as shown below.
Pdmax(W) = (Tjmax(°C) - Ta(°C)) /θja
Pdmax: Maximum Power Dissipation, Tjmax: Junction Temperature = 125°C
Ta: Ambient Temperature, θja: Thermal Resistance of package(SSOP20) = 333°C/W
Power dissipation of the NJU8755 itself is calculated, as shown below.
Pd(W) = PO(W) X RO(Ω) / RL(Ω) + PdIC(W)
Pd: Power Dissipation, PO: Output Power, RO: Internal Resistance(output driver)
RL: Load Resistance, PdIC: Power of internal circuit
NJU3555NJU8755
-5-
Ver.2008-11-19
ELECTRICAL CHARACTERISTICS
(Ta=25°C, VDD= VDDL= VDDR=5.0V, VSS=VSSL=VSSR=0V, Input Signal=1kHz,
Input Signal Level=200mVrms, Frequency Band=20Hz~20kHz,
Load Impedance=8Ω, 2nd-order 34kHz LC Filter(Q=0.85))
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNIT Note
VDD,VDDP,VDDN Supply Voltage VDD 2.7 5.0 5.25 V
Input Impedance ZIN INL, INR pins - 20 - kΩ
Voltage Gain AV - 23 - dB
Output Power Efficiency Eeff Output THD=10% 80 - - %
Output THD THD Po=0.6W - 0.05 0.08 % 5
Output Power Po Output THD=10% - 1.2 - W/ch
S/N SN A weight - 80 - dB 5
Dynamic Range Drange A weight - 83 - dB 5
Channel Separation Echn EIAJ(1kHz) 60 - - dB
Output Level Difference
Between L- and R- channels CHD - - 3 dB
Maximum Mute Attenuation MAT 90 - - dB
Operating Current (Standby) IST - - 1 µA
Operating Current
(No signal input) IDD No Filter
No Load - 7.5 10 mA
VIH MUTE, STBY pins 0.7VDD - VDD V
Input Voltage VIL MUTE, STBY pins 0 - 0.3VDD V
Input Leakage Current ILK MUTE, STBY pins - - ±1.0 µA
Note 5) Test system of the output THD, S/N and Dynamic Range
The output THD, S/N and dynamic range are tested in the system shown in Figure1, where a 2nd-order
LC LPF and another filter incorporated in an audio analyzer are used.
2nd-order LPF : fc=34kHz / Refer to “Typical Application Circuit”.
Filters : 22Hz HPF + 20kHz LPF(AES17)
(with the A-Weight filter for S/N and Dynamic-range tests)
Input Signal
THD
Measuring
Apparatus
Filter
20kHz
(AES17)
2nd-orde
r
LC LPF
NJU8755 Test Board Audio Analyzer
Figure 1. Output THD, S/N and Dynamic Range Test System
NJU8755
NJU8755
- 6 - Ver.2008-11-19
TYPICAL APPLICATION CIRCUIT
<LCR Filter Configuration>
<LR Filter Configuration>
Figure 2.1. Application Circuit example
NJU8755
VDD(1)
VSS(20)
OUTLP(6)
OUTLN(8)
22
µ
H
1
µ
F
8Ω Speaker
22
µ
H 1
µ
F
VDDL
(
5,9,10
)
VSSL(7)
0.1
µ
F 10µFVDD
0.1µF
10µF
VDD
INL(2)
INL
COM(18)
MUTE(4)
STBY(17)
TEST(3)
2.2µF
10µF
VDDR
(
11,12,16
)
VSSR(14)
0.1
µ
F10µFVDD
OUTRP(15)
OUTRN(13)
22
µ
H
1
µ
F
8Ω Speaker
22
µ
H 1
µ
F
INR(19)
INR 2.2µF
A918CY-220M
A918CY-220M
•
A918CY-220M is manufactured by TOKO, INC.
For detail information, please refer its technical papers.
A918CY-220M
A918CY-220M
Figure 2.2. Application Circuit example
NJU8755
VDD(1)
VSS(20)
OUTLP(6)
OUTLN(8)
33
µ
H
8Ω Speaker
VDDL
(
5,9,10
)
VSSL(7)
0.1
µ
F 10µFVDD
0.1µF
10µF
VDD
INL(2)
INL
COM(18)
MUTE(4)
STBY(17)
TEST(3)
2.2µF
10µF
VDDR
(
11,12,16
)
VSSR(14)
0.1
µ
F10µFVDD
OUTRP(15)
OUTRN(13)
33
µ
H
8Ω Speaker
INR(19)
INR 2.2µF
NJU3555NJU8755
-7-
Ver.2008-11-19
Using the LCR filter the power consumption is somewhat lower than using the LR filter power consumption when
no signal input. The THD+N is somewhat influenced by the LR filter more than the LCR filter. Please test the
circuit carefully to fit your application.
Note 6) 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 7) The power supply for VDDL and VDDR 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 capacitor is small.
Note 8) 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 9) The transition time for MUTE and STBY signals must be less than 100µs. Otherwise, a malfunction may
be occurred.
Note 10) (1) – (20) indicates pin number.
[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.
