
TB2902HQ 
2004-08-18 
3
Caution and Application Information 
(description is made referring 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 (except by 
software). However, this feature makes possible space and cost saving. 
The amplifier gain, G
V
=
 26dB, is calculated using the expression below: 
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 
In the case when G
V
=
 12dB selected via I
2
C, G
V1
 changed from 0dB to 
14dB so that the output 
dynamic range is reduced as the output of Amp.1 is attenuated. 
2. Muting Time Constant and Pop Noise Suppression when V
CC
 Rapidly Falls 
(pin 16)
The capacitor C4 at pin 16 is for muting time 
constant to suppress the pop noise. The larger 
value capacitor is used, the lower pop noise 
becomes but the longer the muting time from the 
mute ON command sent to muting an output 
sound actually. The charge period, which makes 
the delay of muting after "Mute On" command is 
written, is MIN=30msec, MAX=180msec in case 
of C4 (Pin 16) = 1 uF, Vcc=9 to 18V and Tj = -40 
to 150 degrees condition. 
As the V
CC
 is rapidly falling, the IC internal low 
voltage muting operates to eliminate the large 
pop noise basically. 
If the effect of the internal low voltage muting 
is not enough in such a case, make this pin 16 set 
at low: 5 V and less by external circuit for more 
effective to suppress the pop noise. 
In this case, this pin 16 has to be released from setting at low before going back to play mode. 
Additionally, the initial state after turning the amplifier “ON” or after turning stand by “off” by  I
2
C Bus 
is muted, so that it is necessary to send a  “mute off” command to change from this condition to play mode. 
Caution on the use of the muting function 
The audio muting function is enabled when pin 16 is not set Low. While the time constant of the muting 
function is determined by the value of C4, the designer should take into account the possible generation of 
pop noise during switching operations. The pop noise which is generated when the power or muting 
function is turned ON/OFF will vary according to the time constant set by capacitor C4 value.  
In the case when C4 value is large and the time constant is long, pop noise will be suppressed during the 
time interval when the voltage on pin 16 is falling.  
However, the pop noise may become apparent as a “peaky” sound if the mute ON or OFF command is 
sent from 
μ
Controller while the voltage at pin 16 is rising.  
Amp. 1
Input
Amp. 2A
Amp. 2B
Figure 1  Block Diagram 
To mute circuit
From low voltage 
muting circuit 
16
C
1
μ
F
Figure 2  Pin 16 Muting Circuit