382
Optical disc ICs
4-channel BTL driver for CD players
BA6896FP
The BA6896FP is a 4-channel BTL driver designed for CD player motor and actuator drives. The internal 5V regulator
and standard operational amplifier make this IC suitable for a wide spectrum of applications.
F
Applications
CD players, CD-ROM drives
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Features
1) HSOP 28-pin package, for application miniaturiza-
tion.
2) A minimum of attached components.
3) Driver gain is adjustable with a single attached resis-
tor.
4) Internal 5V regulator. (requires attached PNP tran-
sistor)
5) Internal standard operational amplifier.
6) Internal thermal shutdown function.
7) The output current between pins 1 and 2 is mutable
with the external mute pin.
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Absolute maximum ratings (Ta = 25
_
C)
387
Optical disc ICs
BA6896FP
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Circuit operation
(1)
Driver
Inputs to the IC are the focus tracking error signal from
the servo preamplifier and the control signal from the mo-
tor. The input signals, which normally center on 2.5V, are
V / I converted by the preamplifier, generating a current
corresponding to the input voltage. This current is
passed through a resistor and into the internal reference
voltage component, the preamplifier output being a sig-
nal centering on the internal reference voltage. Two sys-
tems (positive phase and negative phase) are created
during V / I conversion, generating BTL output via the
driver buffer.
(2)
Regulator
This is a typical series regulator that generates a refer-
ence voltage internally. A PNP low saturation transistor
must be connected.
(3)
Operational amplifier
A standard 4558 type.
389
Optical disc ICs
BA6896FP
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Operation notes
(1)
The BA6896FP has an internal thermal shutdown
circuit. Output current is muted when the chip tempera-
ture exceeds 175
_
C (typically).
(2)
The output current can be muted be raising the
mute pin (pin 7) voltage above 2.2V. Pin 7 should be open
or pulled up above 0.4V during normal operation.
(3)
Muting also occurs when the bias pin (23 pin) drops
below 1.4V (typically). Pin 23 should stay above 1.6V
during normal operation.
(4)
The internal circuits turn off when the supply volt-
age drops below 4.5V (typically) and start up again when
the supply voltage rises above 4.7V (typically).
(5)
Muting occurs during thermal shutdown, mute-on
operations or a drop in the bias pin voltage or supply volt-
age. In each case, only the drivers are muted. During
muting, the output pins remain at the internal bias volt-
age, roughly (V
CC
*
V
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) / 2.
(6)
Attach a bypass capacitor (roughly 0.1
F) to the
power supply, at the base of the IC.
(7)
The radiating fin is connected to the package's in-
ternal GND, but should also be connected to an external
ground.
(8)
The capacitor between regulator output (pin 6) and
GND also serves to prevent oscillation of the IC, so select
one with good temperature characteristics.
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Thermal derating curve
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Electrical characteristic curves
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