20 W 2-channel BTL AF Power Amplifier
for Car Stereos
Overview
The LA4708 is a BTL two-channel power IC for car audio
developed in pursuit of excellent sound quality. Low-region
frequency characteristics have been improved through the use
of a new NF capacitorless circuit, and crosstalk which causes
``muddy'' sound has been reduced by improving both circuit
and pattern layout. As a result, the LA4708 provides powerful
bass and clear treble. In addition, the LA4708 features on-chip
protectors and standby switch. The LA4708 is also
pin-compatible with the LA4705NA (car stereo-use 17 W
two-channel power IC), and can be substituted for the
LA4705NA for higher power. (When the board is shared, pins
1 and 9 must be left open.)
Features
.
High power: supports total output of 30 W + 30 W
(V
CC
= 13.2 V, THD = 30%, R
L
= 4
)
.
Supports R
L
= 2
(P
O
= 30 W when V
CC
= 13.2 V,
THD = 10%)
.
Designed for excellent sound quality
(f
L
< 10 Hz, f
H
= 130 kHz)
.
NF capacitorless
.
Any on time settable by external capacitor
.
Less pop noise
.
Standby switch circuit on chip (microprocessor supported)
.
Various protectors on chip
(output-to-ground short/output-to-V
CC
short/
load short/overvoltage/thermal shutdown circuit)
Package Dimensions
unit: mm
3109-SIP18H
[LA4708]
SANYO : SIP18H
Specifications
Maximum Ratings
at Ta = 25°C
Parameter
Symbol
Conditions
Ratings
Unit
Maximum supply voltage
V
CC
max 1
No signal, t = 60 s
24
V
V
CC
max 2
16
V
Surge supply voltage
V
CC
surge
t
%
0.2 s, single giant pulse
50
V
Maximum output current
I
O
peak
Per channel
4.5
A
Allowable power dissipation
Pd max
Arbitrarily large heat sink
37.5
W
Operating temperature
Topr
35 to +85
°C
Storage temperature
Tstg
40 to +150
°C
* Set V
CC
, R
L
in a range that does not exceed Pd max = 37.5 W
Ordering number: EN5245A
Monolithic Linear IC
LA4708
SANYO Electric Co.,Ltd. Semiconductor Bussiness Headquarters
TOKYO OFFICE Tokyo Bldg., 1-10, 1 Chome, Ueno, Taito-ku, TOKYO, 110 JAPAN
93096HA(II)/13096HA(II) No.5245-1/9
Operating Conditions
at Ta = 25°C
Parameter
Symbol
Conditions
Ratings
Unit
Recommended supply voltage
V
CC
13.2
V
Operating voltage range
V
CC
op
Range where Pd max is not exceeded
9 to 16
V
Recommended load resistance
R
L
4
Recommended load resistance range
R
L
op
2 to 4
Operating Characteristics
at Ta = 25°C, V
CC
= 13.2 V, R
L
= 4
, f = 1 kHz, Rg = 600
Parameter
Symbol
Conditions
min
typ
max
Unit
Quiescent current
I
CCO
70
150
250
mA
Standby current
Ist
10
60
µA
Voltage gain
VG
38
40
42
dB
Total harmonic distortion
THD
P
O
= 2 W
0.07
0.4
%
Output power
P
O
1
THD = 10%
16
20
W
P
O
2
THD = 10%, V
CC
= 14.4 V
24
W
P
O
3
THD = 10%, R
L
= 2
30
W
Output offset voltage
V
N
offset
Rg = 0
300
+300
mV
Output noise voltage
V
NO
Rg = 0, B.P.F. = 20 Hz to 20 kHz
0.1
0.5 mVrms
Ripple rejection ratio
SVRR
Rg = 0, f
R
= 100 Hz, V
R
= 0 dBm
40
50
dB
Channel separation
CHsep
Rg = 10 k
, V
O
= 0 dBm
50
60
dB
Input resistance
r
i
21
30
39
k
Standby pin applied voltage
Vst
Amp on, applied through 10 k
2.5
V
CC
V
Allowable
power
dissipation,
Pd
max
--
W
Arbitrarily large heat sink
Ambient temperature, Ta -- °C
Heat
sink
thermal
resistance,
f
--
°C/W
Al heat sink, t = 1.5 mm
Tightening torque 39 N
c
cm
With silicone grease applied
Heat sink area, S
f
-- cm
2
LA4708
No.5245 -2/9
Equivalent Circuit Block Diagram
Each Pin Voltage
V
CC
= 13.2 V, 5 V applied through STBY = 10 k
, R
L
= 4
, Rg = 0
Pin No.
1
2
3
4
5
6
Name
IN1
DC
Pre-GND
STBY
ON TIME
Pin voltage (V)
0.29
1.58
6.55
0
3.2
2.28
Pin No.
7
8
9
10
11
12
Name
IN2
POP
N.C
V
CC
2
OUT 2
Pin voltage (V)
1.58
2.08
0.29
0
13.2
6.5
Pin No.
13
14
15
16
17
18
Name
PWRGND 2
+OUT 2
+OUT 1
PWRGND 1
OUT 1
V
CC
1
Pin voltage (V)
0
6.5
6.5
0
6.5
13.2
Pins 1,9 : Don't use
Pin 10 : No connection
-
-
-
-
LA4708
No.5245 -3/9
Sample Print Pattern
Description of External Components
C1, C4
Input capacitors
2.2 µF is recommended. f
L
can be varied by C1, C4 capacitances to adjust the
bass range.
C2
Decoupling capacitor
(ripple filter)
C3
Amplifier on time setting
capacitor
Approximately 0.8 second for 33 µF. Since the on time is proportional to this
capacitance, it can be set as desired by varying this capacitance.
(Refer to the characteristics curve.)
C5
Power supply capacitor
C6, C7, C8, C9
Oscillation blocking capacitors
Use polyester film capacitors (Mylar capacitors) with good temperature
characteristics. (R2, R3, R4, and R5 used jointly.) Since stability may be
affected slightly by the pattern layout, etc., 0.1 µF or more is recommended.
R1
Standby switch current limiting
resistor
10 k
is recommended (when the applied voltage for the standby switch is
2.5 V to 13.2 V). This resistor cannot be removed.
Copper foil area 90
×
105 mm
2
LA4708
No.5245 -4/9
Features of IC Inside and Usage Notes
Standby function
.
Pin 5 is the standby switch pin. The amplifier is turned on by applying approximately 2.5 V or more to this pin through an
external resistor (R1).
.
If voltage in excess of 13.2 V is to be applied to the standby switch, calculate the value of R1 using the following formula so
that the current flowing into pin 5 is 500 µA or less:
Mute function
.
Pin 6 is the connector for the capacitor that determines the on time in order to prevent pop noise. By grounding this pin, the
amplifier can implement mute operation. In this case, the recovery time depends on C3.
How to reduce pop noise
.
Although the LA4708 reduces pop noise, an electrolytic capacitor of between 0.47 and 2.2 µF can be connected between pin 8
and the pre-GND to further reduce pop noise that occurs when power supply is turned on/off (standby switch on/off). The larger
the capacitance, the lower the frequency of pop noise, and it is barely audible, but sound residue of the sound signal is liable to
linger when power is turned off. Pin 8 is the bias pin for the output amplifier and normally is left open.
Protectors
.
In an output-to-ground and output-to-V
CC
short protector system configuration, if a DC resistor is connected between amplifier
output pin and GND, the protector may operate, causing the amplifier not to start operating. Therefore, as a general rule, no DC
resistor should be connected between amplifier output pin and GND.
.
In order to prevent damage or degradation which may be caused by abnormally heated IC, the LA4708 has a thermal shutdown
protector. Accordingly, if the IC junction temperature (Tj) climbs to around 170 to 180°C due to inadequate heat dissipation, the
thermal shutdown protector will operate to control the output gradually into attenuation.
.
Also be fully careful of handling other protectors built in the LA4708.
Miscellaneous
.
Since pins 1 and 9, which are unused, are connected internally, they must be left open.
.
Pin 10 is an NC pin (no internal connection).
R1 =
Applied voltage - 1.4 V
10 k
500 µA
Standby
applied voltage
500 µA or less
About 1.4 V
(2VBE
)
Pin 5 Equivalent
circuit internal IC
LA4708
No.5245 -5/9
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