Rainbow Electronics BA6239AN - Manual (Page 5)

494
Motor driver ICs BA6238A / BA6238AN / BA6239A / BA6239AN
F
Circuit operation
(1) Input (pins 4, 5, and 6)
These pins receive control logic signals. The relevant cir-
cuits are designed to have hysteresis and antinoise char-
acteristics. The input circuit can control the logic by input
currents of a few microamperes or more. The motor con-
nected between pins 10 and 2 is selected when pin 4 is
HIGH and pin 5 is LOW, while the motor connected be-
tween pins 10 and 3 is selected when pin 5 is HIGH and
pin 4 is LOW. Pin 6 is the forward / reverse control input
pin.
(2)
Output (pins 2, 3, and 10)
Pin 10 is the common pin. Either pin 2 or 3 is left OPEN
during motor driving. The waveform monitored on the
OPEN pin will be the same as that on pin 10.
( 1) BA6238A / BA6238AN
The output stage configuration of the BA6238A /
BA6238AN is shown in Fig. 5. The output stage contains
NPN transistors in a Darlington configuration, which
means the saturation voltage between V
CC1
and the out-
put pin is rather high but the output voltage can be easily
set by using a zener diode or a resistor voltage divider.
The voltage on the V
R
pin can be varied from 0V to V
CC1
.
The output voltage is at the maximum when pin 8 is
OPEN.
V
OH
=V
CC1
–V
sat
(PNP)–2 V
BE
(NPN Darlington)
V
OL
=V
sat
(NPN Darlington)
V
sat
and V
BE
are functions of the output current (see Fig.
17).
( 2) BA6239A / BA6239AN
The output configuration of the BA6239A / BA6239AN is
shown in Fig. 6. Because the output stage contains only
one NPN transistor, the saturation voltage between pin
8 and the output pin is about 0.7V less than that in the
BA6238A. The output voltage is controlled by the pin-8
voltage. The voltage on the V
R
pin can be varied from 8V
to V
CC1
. The output voltage is at the maximum when pin
8 is V
CC1
.
V
OH
=V
R
–V
sat
(PNP)–V
BE
(NPN)
V
OL
=V
sat
(NPN Darlington)
V
sat
and V
BE
are functions of the output current (see Fig.
18).
(3)
Output control (pin 8)
Output voltage can be varied by controlling the pin-8 volt-
age.
( 1) BA6238A / BA6238AN
The pin-8 voltage can vary from 0V to V
CC
. Because a
constant current (0.6mA typically) flows out from pin 8,
the output voltage can be controlled by using a zener
diode or a resistor voltage divider.
( 2) BA6239A / BA6239AN
In addition to controlling the output voltage, pin 8 supplies
base current to the high-side output transistor (NPN).
(4)
Power supply (pins 7 and 9)
Pin 7 supplies power to the input, logic, and thermal shut-
down circuits. Pin 9 supplies power to the output transis-
tors.
(5)
Thermal shutdown circuit
Regardless of the input mode, the thermal shutdown cir-
cuit puts the outputs to LOW level when the chip temper-
ature rises due to such an event as motor locking. When
the thermal shutdown circuit is deactivated, the outputs
revert to the status determined by input mode.
The thermal shutdown circuit is activated when the chip
temperature exceeds 150
_ C (125 _ C minimally), and
deactivated when the chip temperature drops to 100
_
C
(125
_
C maximally). The minimum temperature differ-
ence between the activation and deactivation settings is
10
_
C.
(6) Ground pin and fins
Pin 1 and the fins have the minimum potential within the
IC. The PCB design should ensure that the common im-
pedance is kept as low as possible when a large current
flows.