Product specifications

DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 37 of 80
Sharp Electronics (UK) Limited - May 2003
Revision 3
Class D Output Stages
Sharp have used class D output stages for a number of years in discrete component form, but now these are
incorporated into specially designed integrated circuit.
These devices are ideal for use with television audio and vertical output stages where high efficiency (low energy
use) is required. A TDA7480 is used for audio and vertical outputs and the TDA7481 to drive the sub-woofer in
the Dolby Pro-Logic versions of the chassis. The following table defines the operation of each pin of the
TDA7480.
Pin Name Function Nominal Voltage Pin
1 -VCC Negative Supply Voltage
-13.1V
1
2 -VCC Negative Supply Voltage
-13.1V
2
3 -VCC Negative Supply Voltage
-13.1V
3
4 OUT PWM Output
0V
4
5 BOOTDIODE Bootstrap Diode Anode
-2.1V
5
6 BOOT Bootstrap Capacitor
9.9V
6
7 NC Not Connected
0V
7
8 FEEDCAP Feedback Integrating Capacitor
0V
8
9 FREQUENCY Frequency Setting Resistor
-11.8V
9
10 SGN-GND Signal Ground
0V
10
11 IN Input
0V
11
12 ST-BY-MUTE Standby/Mute Control Pin
5.0V
12
13 NC Not Connected
0V
13
14 +VCC SIGN Positive Signal Supply Voltage
14.1V
14
15 VREG 10V Internal Regulator
-2.1V
15
16 +VCC POW Positive Power Supply Voltage
14.1V
16
17 -VCC Negative Supply Voltage (De-coupled by 100nF)
-13.1V
17
18 -VCC Negative Supply Voltage
-13.1V
18
19 -VCC Negative Supply Voltage
-13.1V
19
20 -VCC Negative Supply Voltage
-13.1V
20
Note that pins 1, 2, 3, 17, 18, 19 and 20 are all connected together by a large area of print on the bottom of the
PWB. This area is used as a heatsink for the device. It is very important that all these legs are connected when
replacing the device, as premature failure may occur if they are not. It is also worth noting that when correctly
fitted the IC itself does not get hot during operation.
Pins 8 and 9 – Frequency
The external components on these pins will determine the base frequency of the PWM section of this device.
Remember for the audio circuit the frequency will vary from the base frequency by at least the bandwidth of
the audio signal (20kHz). This ensures that no beat signal is produced which could interfere with the main audio
signal itself.
Pin 12 – Standby/Mute Control Pin
The voltage at pin 12 will determine the working condition of this device. A voltage of less than 0.8v will tell the
device to switch to standby (no output), a voltage between 1.8V to 2.5V will result in the output being attenuated
between 60 to 80 dB. For normal operation the voltage at pin 12 should be greater than 2.7V.