Philips 900 Series - Page 16

SIRCUIT DESCRIPTION
AUXILIARY
CHANNELS OARS
[ao ie
a
WRITE (1) ERASE 7 +h)
(DATA CHANNEL
PLAYBACK)
26
CONTROL | ss ConTRones§
A
a eel TERAUX
(AUXILIARY | (AUXILIARY
CHANNEL CHANNEL
a =
WRITE (I, + I,) 1
ERASE (I, +1, +1.) 1
3.1.2.2 current amplifier
The write current at the outputs is regulated
by the current amplifier. The value of the
current I, is set by resistor R, 3887,
connected between pin 2 (RD) and V,,. The
current through this R, (3387) also fiows at
the outputs. The current amplifier regulates
the voltage across R,, which is measured
between RSENSE and GNDD (pins 3 and 4),
to a value of 150mV. This force-sense
technique eliminates the influence of parasitic
series impedances.
The output of the current amplifier is internally
Switched to the output pins QA to QJ. During
AUX write (outputs QA and OB active) an
additional current |, is added to the write
current. This current can be controlled by
resistor R, (8886) connected between RX (pin
1) and GNDD. R, is chosen to be 6.7 x R, for
achieving 1.2dB current increase.
During the erase mode of the auxiliary
channel (TERAUX = HIGH, see above table)
it is possible to let an additional output
current |, flow through QA and QB (pins 23
and 22). This extra current (Erase source)
can be adjusted with an external resistor R,
(3885) connected between pin 6 and GNDD.
Pin 5 (V,,.) is externally connected to ground
(GNDD).
3.1.2.3 Voltage reference
A reference voltage is available at pin 9
(REF). This voltage is derived from a
bandgap reference source and can be used
to modify the voltage sensed by the current
amplifier, e.g. for external temperature
compensation.
"X = don't care; 0 = LOW: ] = HIGH.
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0
0 iS oa |
3.1.2.4 outputs
Each channel is selected in sequence.
Depending on the dataword, the current is
directed forward or reversed through the
heads. The outputs that are not selected are
kept floating to prevent any incorrect current
flow. In the HIGH state (one of the switches
At to J1 is closed) the output is internally
connected to a fixed voltage V,,. in the LOW
state (one of the switches AO to JO is closed)
the output is connected to the current
amplifier.
3.1.2.5 clamp circuit
During the periods that the head elements
are not selected, the clamp circuit
accommodates the write current. This current
is directed through the resistors 3881, 3882,
3884 in shunt circuit from pin 24 to the
supply. The clamping results in a constant
current being drawn from the supply and
therefore reduces emission of interferences.
3.1.2.6 standby mode.
The circuit is in the standby mode when
TDAPLB = 1 and TAUPLB = 1, or when a
HIGH level is applied to pin 10. After a HIGH-
to-LOW transition at pin 10, the IC will remain
in the standby mode until TDAPLB = 0 or
TAUPLB = 0. When the IC is in the standby
mode, the current amplifier is switched off to
minimize the power consumption, switches A
to J are open-circuit and the voltage
reference and the erase source are switched
off.
3.1.2.7 Protection
The IC is immediately switched to standby
mode when a short-circuit to ground at an
output pin is detected (V, < 0.5V). When the
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27 CIRCUIT DESCRIPTION
short-circuit condition is removed, the IC will
resume operation. The state of the decoder is
not affected by a "SHORT".
Fig. 17 Write IC TDA1319T
3.1.2.8 Adjustment
The adjustment of the write current has been
described in paragraph 2.4.
3.1.2.9 Block diagram and pin
configuration TDA1319T
TDA1319T
TS yo st Ra ee a a hE Er ee
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