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TDA1085C View Datasheet(PDF) - Motorola => Freescale

Part Name
Description
Manufacturer
TDA1085C
Motorola
Motorola => Freescale Motorola
TDA1085C Datasheet PDF : 12 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
TDA1085C
Trigger Pulse Generator (Pins 1, 2, 5, 13, 14, 15)
This circuit performs four functions:
The conversion of the control amplifier DC output level to a
proportional firing angle at every main line half cycle.
The calibration of pulse duration.
The repetition of the pulse if the triac fails to latch on if the current
has been interrupted by brush bounce.
The delay of firing pulse until the current crosses zero at wide firing
angles and inductive loads.
RPin 15 programs the Pin 14 discharging current. Saw tooth signal is
then fully determined by R15 and C14 (usually 47 nF). Firing pulse
duration and repetition period are in inverse ratio to the saw tooth
slope.
Pin 13 is the pulse output and an external limiting resistor is
mandatory. Maximum current capability is 200 mA.
Current Limiter – (Pin 3) Safe operation of the motor and triac under
all conditions is ensured by limiting the peak current. The motor
current develops an alternative voltage in the shunt resistor (0.05
in Figure 4). The negative half waves are transferred to Pin 3 which
is positively preset at a voltage determined by resistors R3 and R4.
As motor current increases, the dynamical voltage range of Pin 3
increases and when Pin 3 becomes slightly negative in respect to
Pin 8, a current starts to circulate in it. This current, amplified
typically 180 times, is then used to discharge Pin 7 capacitor and, as
a result, reduces firing angle down to a value where an equilibrium is
reached. The choice of resistors R3, R4 and shunt determines the
magnitude of the discharge current signals on CPin 7.
Notice that the current limiter acts only on peak triac current.
APPLICATION NOTES
(Refer to Figure 4)
Printed Circuit Layout Rules
In the common applications, where TDA 1085C is used, there is on
the same board, presence of high voltage, high currents as well as
low voltage signals where millivolts count. It is of first magnitude
importance to separate them from each other and to respect the
following rules:
Capacitor decoupling pins, which are the inputs of the same
comparator, must be physically close to the IC, close to each other
and grounded in the same point.
Ground connection for tachogenerator must be directly connected
to Pin 8 and should ground only the tacho. In effect, the latter is a
first magnitude noise generator due to its proximity to the motor
which induces high dφ/dt signals.
The ground pattern must be in the “star style” in order to fully
eliminate power currents flowing in the ground network devoted to
capacitors decoupling sensitive Pins: 4, 5, 7, 11, 12, 14, 16.
As an example, Figure 5 presents a PC board pattern which
concerns the group of sensitive Pins and their associated capacitors
into which the a.m. rules have been implemented. Notice the full
separation of “Signal World” from “Power”, one by line AB and their
communication by a unique strip.
These rules will lead to much satisfactory volume production in the
sense that speed adjustment will stay valid in the entire speed
range.
Power Supply
As dropping resistor dissipates noticeable power, it is necessary to
reduce the ICC needs down to a minimum. Triggering pulses, if a
certain number of repetitions are kept in reserve to cope with motor
brush wearing at the end of its life, are the largest ICC user. Classical
worst case configuration has to be considered to select dropping
resistor. In addition, the parallel regulator must be always into its
dynamic range, i.e., IPin 10 over 1.0 mA and VPin 10 over 3.0 V in any
extreme configuration. The double filtering cell is mandatory.
Tachogenerator Circuit
The tacho signal voltage is proportional to the motor speed. Stablility
considerations, in addition, require an RC filter, the pole of which
must be looked at. The combination of both elements yield a constant
amplitude signal on Pin 12 in most of the speed range. It is
recommended to verify this maximum amplitude to be within 1.0 V
peak in order to have the largest signal/noise ratio without resetting
the integrated circuit (which occurs if VPin 12 reaches 5.5 V). It must
be also verified that the Pin 12 signal is approximately balanced
between “high” (over 300 mV) and “low”. An 8–poles tacho is a
minimum for low speed stability and a 16–poles is even better.
The RC pole of the tacho circuit should be chosen within 30 Hz in
order to be as far as possible from the 150 Hz which corresponds to
the AC line 3rd harmonic generated by the motor during starting
procedure. In addition, a high value resistor coming from VCC
introduces a positive offset at Pin 12, removes noise to be interpreted
as a tacho signal. This offset should be designed in order to let Pin 12
reach at least – 200 mV (negative voltage) at the lowest motor speed.
We remember the necessity of an individual tacho ground
connection.
Frequency to Voltage Converter – F V/C
CPin 11 has a recommended value of 820 pF for 8–poles tachos and
maximum motor rpm of 15000, and RPin 11 must be always 470 K.
RPin 4 should be choosen to deliver within 12 V at maximum motor
speed in order to maximize signal/noise ratio. As the FV/C ratio as
well as the CPin 11 value are dispersed, RPin 4 must be adjustable and
should be made of a fixed resistor in serice with a trimmer
representing 25% of the total. Adjustment would become easier.
Once adjusted, for instance at maximum motor speed, the FV/C
presents a residual non linearity; the conversion factor (mV per RPM)
increases by within 7.7% as speed draws to zero. The guaranteed
dispersion of the latter being very narrow, a maximum 1% speed
error is guaranteed if during Pin 5 network design the small set
values are modified, once forever, according this increase.
The following formulas give VPin 4:
+ @ @ @ @ @ ) ) VPin 4
G.0
(VCC–Va)
CPin 11
R4
f
(1
1 120k In volts.
RPin11
' G.0 . (VCC – Va) 140
Va = 2.0 VBE
120 k = Rint, on Pin 11
Speed Set – (Pin 5) Upon designer choice, a set of external
resistors apply a series of various voltages corresponding to the
various motor speeds. When switching external resistors, verify that
no voltage below 80 mV is ever applied to Pin 5. If so, a full circuit
reset will occur.
MOTOROLA ANALOG IC DEVICE DATA
5
 

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