LA4905.PDF

Ordering number : EN5504

Monolithic Linear IC

LA4905

17-W, 2-Channel BTL AF High-Efficiency

Power Amplifier for Car Stereo Systems

Overview

The LA4905 is a BTL 2-channel power amplifier IC for

use in car audio systems. Increases in the number of

external components are held to a minimum by adopting

both a signal-following type switching scheme in the

amplifier’s output stage power supply, and a newly-

developed nonlinear amplifier that has nonlinear

characteristics in the signal system. The power dissipation

(thermal loss) in the actual operating range has been

reduced to about 1/2 that of earlier class B amplifier ICs.

This contributes significantly to miniaturization of the heat

sink and to reduction of heating within the set.

Package Dimensions

unit: mm

3160-SIP23HZ

[LC4905]

Features

• Power dissipation reduced by 50% (When average

music power is measured, and when compared to earlier

Sanyo products.)

• The number of required signal follower circuits has been

reduced to a single circuit for two channels, allowing the

number of external components to be reduced.

• The output is a pure analog signal: no switching noise is

output to the output lines.

• Operates on an 8 to 18-V single-voltage power supply.

• Full complement of built-in protection circuits (shorting

to the power supply, shorting to ground, overvoltage,

and thermal protection)

• Built-in standby switch

SANYO: SIP23HZ

Specifications

Maximum Ratings at Ta = 25°C

Parameter

Symbol

Conditions

Ratings

Unit

V CC max1

No input, t = 1 minute

Maximum supply voltage

V CC max2

Maximum output current

I O Peak

(Per channel)

4.5

Allowable power dissipation

Pd max

With an arbitrarily large heat sink

37.5

Operating temperature

Topr

–35 to +85

°C

Storage temperature

Tstg

–40 to +150

°C

Notes: 1. Set VCC and RL in the range where Pd max does not exceed 37.5 W.

2. The overvoltage protection circuit operates when VCC is 20 V or higher.

SANYO Electric Co.,Ltd. Semiconductor Bussiness Headquarters

TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, Taito-ku, TOKYO, 110 JAPAN

83096HA (OT) No. 5504-1/10

LA4905

Operating Conditions at Ta = 25°C

Parameter

Symbol

Conditions

Ratings

Unit

Recommended supply voltage

V CC

13.2

Allowable operating supply voltage range

V CC op

8 to 18

Recommended load resistance

R L

Recommended load resistance range

R L op

2 to 4

Notes:Set VCC and RL in the range where Pd max does not exceed 37.5 W.

Operating Characteristics at Ta = 25°C, V CC = 13.2 V, R L = 4

, f = 1 kHz, Rg = 600

, in the recommended circuit

Parameter

Symbol

Conditions

min

typ

max

Unit

Quiescent current

Icco

R L = ° , V IN = 0

110

150

Standby current

Ist

µA

Voltage gain

V O = 0 dBm

Total harmonic distortion

THD

P O = 1W, LPF = 30 kHz

0.07

0.2

P O 1

THD = 10%, R L = 4 ½

Output power 1

P O 2

THD = 10%, R L = 2 ½

Output noise voltage

V NO

Rg = 0, BPF = 20 Hz to 20 kHz

0.15

0.3

mVrms

Ripple rejection ratio

SVRR

Rg = 0, V CCR = 0 dBm, BPF = 20 Hz to 20 kHz

Channel separation

CHsep

Rg = 10 k ½ , V O = 0 dBm, BPF = 20 Hz to 20 kHz

Input resistance

k ½

Output offset voltage

VN offset Rg = 0

–300

+300

Standby on voltage

V STH

AMP = on, applied through a 10 k ½

resistor

V CC

No. 5504-2/10

LA4905

LA4905 High-Efficiency Technology

(1) Signal-following switching scheme

The LA4905 adopts a switching regulator scheme in

the power supply applied to the amplifier output stage.

The LA4905 power dissipation is reduced significantly

by having the output voltage of the switching regulator

follow the input signal. Furthermore, in combination

with the nonlinear amplifier scheme described below,

the LA4905 design reduces the number of switching

regulators to merely one circuit even though it is a

BTL 2-channel amplifier. (See Figure 1.)

(2) Nonlinear amplifier

The LA4905 adopts a nonlinear amplifier that has the

nonlinear characteristics shown in Figure 2 in the

amplifier signal system. This scheme does not use the

center point voltage of 1/2 VCC used in normal

amplifiers, but instead uses a voltage about 2 V lower.

This allows the design to dispense with the lower side

switching regulator.

This nonlinear amplifier has a structure based on a

differential amplifier that has symmetric negative

feedback circuits. Although the BTL output stage

positive and negative phase output waveform is a half-

wave waveform that is expanded and compressed as

shown in Figure 3, the combined output waveform at

the negative load terminal is identical to that output by

earlier products.

No. 5504-3/10

LA4905

Equivalent Circuit Block Diagram

Pin Voltages V CC = 13.2 V, 5 V applied to STBY through a 10-k

resistor, using a digital voltmeter

Pin No.

IN2

Pre-GND

IN1

BEEP

PWR-GND 1

–OUT1

+OUT1

Pin voltage (V)

1.36

2.03

13.0

Pin No.

V CC

V CC (SW)

SW OUT 1

SW OUT 2

SW E

SW B

SW-GND

Pin voltage (V)

3.92

13.2

3.70

3.73

4.0

Pin No.

+OUT 2

–OUT 2

PWR-GND 2

D. C

STAND-BY

N. C

ON-TIME

Pin voltage (V)

2.03

12.1

3.21

2.81

No. 5504-4/10

LA4905

Sample Printed Circuit Board Pattern

1. External Component Functions

C1, C2 • Input capacitors; recommended value: 2.2 µF. Note that the low-frequency band can be adjusted by changing

the values of C1 and C2, since fL depends on their value, although the value must not exceed 3.3 µF (when

C4 is 22 µF) due to pop noise considerations.

C3 • Beep amplifier input capacitor. Use the same value as that used for C1 and C2. Connect the beep amplifier to

PRE-GND through C3 if the beep function is not used.

C4 • Amplifier power-on delay time setting capacitor; recommended value: 22 µF. At the recommended value, the

amplifier will turn on in about 0.7 second after power is applied. The delay time is proportional to the

capacitance and can be set to an arbitrary value. However, a value of 22 µF or larger should be used due to

pop noise considerations.

C5, C6, • Oscillation prevention capacitors. Use capacitors with excellent temperature characteristics such as polyester

film or Mylar capacitors. These capacitors function in conjunction with R1, R2, R3, and R4. We recommend

using capacitors of 0.1 µF or larger, since the stability varies somewhat depending on the printed circuit

board layout.

• Decoupling capacitor (ripple filter)

C10

• Power-supply capacitor

C11

• Switching regulator oscillation prevention capacitor; recommended value: 1500 pF.

C12

• Switching regulator output smoothing capacitor. The LA4905 adopts a self-excitation switching regulator

scheme. Since this capacitor influences the stability of the self-excitation and the regulator efficiency, there is

an optimal value. We recommend the use of a 2.2-µF, 25-V OS capacitor with good temperature

characteristics. Note that a 2.2-

, 1/2-W resistor should be used for R5 for the same reason.

(When the voltage applied to the standby switch is between 3 and 13.2 V.) Note that this resistor cannot be

removed. See the section "Standby Function" elsewhere in this document.

TR1

• External switching transistor. We recommend using a 2SD1668 of rank S. A 2SD1667 of rank S may be used if

the application is designed to handle 4-

loads (R L ). A heat sink must be provided along with that for the IC.

• Flywheel diode that takes up the coil energy. We recommend using an SB40-05J, which is a Schottky barrier

diode with a low V F .

An SB10-05A2 may be used if the application is designed to handle 4-

loads (R L ). A joint heat sink is not

required.

• We recommend the use of the HP-022Z 180-µH coil manufactured by Tokin, Ltd. The 200-µH HP-011Z may

be used if the application is designed to handle 4-

loads (R L ).

No. 5504-5/10

C7, C8

• Standby switch current limiting resistor; recommended value: 10 k

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