TB2903HQ
2004-07-25
3
Caution and Application Method
(Description is made only on the single channel.)
1. Voltage
Gain
Adjustment
This IC has no NF (negative feedback) Pins. Therefore, the voltage gain can not be adjusted, but it makes
the device a space and total costs saver.
The voltage gain of amp.1
: G
V1
= 0dB
The voltage gain of amp.2A, B
: G
V2
= 20dB
The voltage gain of BTL connection : G
V (BTL)
= 6dB
Therefore, the total voltage gain is decided by expression below.
G
V
= G
V1
+ G
V2
+ G
V (BTL)
= 0 + 20 + 6 = 26dB
2. Standby SW Function
(pin 4)
By means of controlling pin 4 (standby pin) to
High and Low, the power supply can be set to ON
and OFF. The threshold voltage of pin 4 is set at
about 3V
BE
(typ.), and the power supply current is
about 2
A (typ.) in the standby state.
Control Voltage of Pin 4: V
SB
Standby Power V
SB
(V)
ON OFF 0~1.5
OFF ON
3.5~6
V
When changing the time constant of pin 4, check the
pop noise.
Advantage of Standby SW
(1)
Since V
CC
can directly be controlled to ON or OFF by the microcomputer, the switching relay can be
omitted.
(2)
Since the control current is microscopic, the switching relay of small current capacity is satisfactory
for switching.
Amp. 1
Input
Amp. 2A
Amp. 2B
Figure 1 Block Diagram
Figure 2 With pin 4 set to High,
Power is turned ON
ON
4
OFF
10 k
to BIAS
CUTTING CIRCUIT
2 V
BE
V
CC
Power
TB2903HQ
2004-07-25
4
3. Muting
Function
(pin 22)
Audio muting function is enabled when pin 22 is Low. When the time constant of the muting function is
determined by R
1
and C
4,
it should take into account the pop noise. The pop noise which is generated when
the power or muting function is turned ON/OFF will vary according to the time constant. (Refer to Figure 4
and Figure 5.)
The pin 22 is designed to operate off 5 V.
Moreover, this terminal (pin 22) serves as the source switch of current of an internal mute circuit. And it is
designed so that the discharge current of this terminal (pin 22) may serve as 200
A. The outside pull-up
resistor R
1
is determind on the basic of this value.
ex) When control voltage is changed in to 6 V from 5 V.
6 V/5 V
47 k = 56 k
To obtain enough mute attenuation, a series resistor, R
1
at pin 22 should be 47 k
or more.
V
CC
Small current capacity switch
Battery
Stand-By
V
CC
From microcomputer
Battery
Stand-By
Standby Switch Method
Figure 3
Conventional Method
V
CC
Large current capacity switch
Battery
V
CC
From
microcomputer
Battery
Relay
Figure 5 Mute Attenuation
-
V
MUTE
(V)
Pin 22 control voltage: VMUTE (V)
ATT V
MUTE
Mute
a
t
tenua
tion
ATT (dB
)
Figure 4 Muting Function
0
-
120
-
100
-
80
-
60
-
40
-
20
0
20
0.5
1
1.5 2 2.5 3
V
CC
=
13.2 V
f
=
1kHz
R
L
=
4
V
OUT
=
20dBm
22
1 k
R
1
5 V
Mute ON/OFF
control
C
4
TB2903HQ
2004-07-25
5
4. Off-set detection function
In case of Appearing output offset voltage by Generating a Large Leakage Current on the input
Capacitor etc.
Figure 6 Application and Detection Mechanism
V
ref
Elec. vol
25
5 V
L.P.F.
To CPU
+
-
V
Offset voltage (at leak or short)
DC Voltage (
-
) Amp (at short) (R
S2
)
DC Voltage (
+
) Amp (at leak) (R
S1
)
V
CC/2
(normal DC voltage)
Leak or short
V
bias
V
ref/2
A
B
R
S2
R
S1
(
+
) Amp output
Threshold level (R
S1
)
V
CC/2
GND
GND
t
t
GND
Voltage of
point (A)
Voltage of
point (B)
Threshold level (R
S2
)
t
R
S2
Figure 7 Wave Form
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