200

Optical disc ICs

BA6295AFP

FCircuit operation

The BA6295AFP comprises a 2-channel driver, internal

bias amplifier, mute pin, and thermal shutdown circuit.

(1)

Driver

The input resistance of the driver is the focus tracking er-

ror signal from the servo preamplifier and the control sig-

nal from the motor. The input signals normally center on

the internal level shift amplifier.

Both positive and negative phases are created during fi-

nal V / I conversion, generating BTL output via the driver

buffer. Because the gain adjustment pins (pins 15, 16, 27

and 28) are external, gain can be adjusted by connecting

a resistor in parallel.

(2)

Internal bias amplifier

increased and crosstalk reduced by connecting a capaci-

tor to pin 23.

(3)

Mute pins

The output current can be muted by switching one of

these pins to the HIGH level. These pins are also used

for thermal shutdown and should always remain at high

impedance during normal operations. This is because

the thermal shutdown feature is disabled when these

pins are at the LOW level.

FOperation notes

(1)

The BA6295AFP has an internal thermal shutdown

circuit. Output current is muted when the chip tempera-

ture exceeds 190

_C (typically).

(2)

Output current can but muted by raising the voltage

between pins 22 and 8 above 1.5V.

(3)

Shorting pins 22 and 8 disables the thermal shut-

down feature.

(4)

Be sure to connect the IC to a 0.1

µF bypass capaci-

tor to the power supply, at the base of the IC.

(5)

The radiating fin is connected to the package’s in-

ternal GND (pin 8), but both it and pin 8 should also be

connected to an external ground.