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PDF BA6870 Data sheet ( Hoja de datos )
| Número de pieza | BA6870 | |
| Descripción | 3-phase motor driver | |
| Fabricantes | ROHM Semiconductor | |
| Logotipo |  |
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Motor driver ICs
3-phase motor driver
BA6870S
The BA6870S is a 3-phase, full-wave, pseudo-linear motor driver suited for VCR capstan motors. The IC has a torque
ripple cancellation circuit to reduce wow and flutter, and an output transistor saturation prevention circuit that provides
superb motor control over a wide range of current. The built-in motor power series regulator allows applications with low
power consumption.
FApplications
3-phase VCR capstan motors
FFeatures
1) 3-phase, full-wave, pseudo-linear driver system.
2) High performance torque ripple cancellation circuit.
3) Reversal braking by detecting the motor direction.
4) Saturation prevention circuit for high- and low-side
output transistors.
5) Motor power supply series regulators.
6) Built-in circuit for output-to-GND short-circuit detec-
tion.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
666
1 page  
Motor driver ICs
BA6870S
(6) Series regulator
The BA6870S has a series regulator output pin. The IC
outputs a sink current according to the HIGH level output
voltage detected.
As shown in Fig. 7 the regulator circuit reduces the power
consumed by the IC by reducing the collector-to-emitter
(C-E) voltage of the driver transistors.
Nearly all the power dissipated by the IC is dissipated be-
tween the collectors and emitters of the output transis-
tors. More power is consumed as the C-E voltage in-
creases and as the output current increases.
The output transistor C-E voltage is equal to the differ-
ence between the supply voltage and the voltage applied
to the motor. Because the voltage across the motor de-
creases with decreasing drive current, the C-E voltage
must increase if the supply voltage is fixed.
Therefore, to improve the efficiency of the driver and to
prevent the power rating of the IC being exceeded, the
supply voltage must be varied in response to changes in
the output current. The supply voltage is decreased at
low current and increased at high current so that no ex-
cessive voltage is applied between the output transistor
collectors and emitters.
(7) Output-to-ground short-circuit detection
The motor output pins of the IC may be short-circuited to
the ground by some fault conditions. A short-circuited
output can destroy the output transistors because of ex-
cessive current, excessive voltage, or both. Even when
a short-circuit condition does not completely destroy the
device, it can still cause extreme overheating. To prevent
this, the BA6870S contains a short-circuit detection cir-
cuit that turns off the motor drive current if the output-to-
ground potential becomes abnormally low.
FOperation notes
The BA6870S has two thermal shutdown circuits (TSD1
and TSD2) to protect the IC. The typical shutdown tem-
peratures are 175_C for TSD1 and 215_C for TSD 2.
When the TSD1 is activated at an elevated chip tempera-
ture, the output pins (pins 1, 3, and 23) are set to the open
state. TSD1 is functional against excessive power dis-
sipation, output short-circuiting, and other irregularities in
the output current, but does not work against overheating
caused by high internal currents due to externally caused
IC damage or pin-to-pin short-circuiting.
When TSD2 is activated at a higher chip temperature, the
high- and low-side output transistors are turned on, and
the internal resistance between the motor power supply
pin (pin 24) and the output ground pin (pin 2) drops to less
than 3Ω. The motor power supply current (IM) is then giv-
en by
VM (V)
IM = RM+R2P+3 (Ω)
Where
IM is the motor supply current
VM is the motor supply voltage,
RM is the motor power supply output resistance,
R2P is the pin-2 resistance.
In your application, make sure to connect between the
motor power supply and pin 24 a circuit breaker that op-
erates at currents less than IM.
670
5 Page | ||
| Páginas | Total 7 Páginas | |
| PDF Descargar | [ Datasheet BA6870.PDF ] | |
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