391
Optical disc ICs
4-channel BTL driver for CD players
BA6897S / BA6897FP
The BA6897S and BA6897FP are a 4-channel BTL driver for CD player motors and actuators. It has an internal 5V
regulator and standard operational amplifier, and is suited to a wide range of applications.
F
Applications
CD players, CD-ROM drives
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Features
1) Minimal number of external components.
2) Driver gain is adjustable with just one attached resis-
tor.
3) Internal 5V regulator (attached PNP transistor nec-
essary).
4) Internal standard operational amplifier.
5) Internal thermal shutdown circuit.
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Absolute maximum ratings (Ta = 25
_
C)
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Recommended operating conditions (Ta = 25
_
C)
398
Optical disc ICs
BA6897S/BA6897FP
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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 corre-
sponding to the input voltage. This current is passed
through a resistor and into the internal reference voltage
component, the preamplifier output being a signal cen-
tering on the internal reference voltage. Two systems
(positive phase and negative phase) are created during
V / I conversion, generating BTL output via the driver buff-
er.
(2)
Regulator
This is a typical series regulator that generates a refer-
ence voltage internally. A PNP low saturation transistor
must be connected.
(3)
Amplifier
General 4558 type.
401
Optical disc ICs
BA6897S/BA6897FP
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Operation notes
(1)
The BA6897S and BA6897FP have an internal
thermal shutdown circuit. Output current is muted when
the chip temperature exceeds 175
_
C (typically).
(2)
If the mute pin voltage is opened or lowered below
0.5V, the output current will be muted. The mute pin
should be pulled up above 2.0V during normal use.
(3)
The bias pin is muted when lowered below 1.4V
(typically). Make sure it stays above 1.6V during normal
use.
(4)
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
F
) / 2.
(5)
Be sure to connect the IC to a 0.1
F bypass capaci-
tor to the power supply, at the base of the IC.
(6)
The radiating fin is connected to the packages inter-
nal GND, but should also be connected to an external
ground.
(7)
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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Electrical characteristic curves
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