ls7262 LSI Computer Systems, Inc., ls7262 Datasheet - Page 2

• Manufacturer Part Number: ls7262
• Description: Brushless Dc Motor Commutator/controller
• Manufacturer: LSI Computer Systems, Inc.

resistor holds the input high when left open. Positive edges at this
input will reset the over-current flip-flop.
OVER-CURRENT SENSE (Pin 12)
This input provides the user a way of protecting the motor
winding, drivers and power supply from an over-load condition.
The user provides a fractional-ohm resistor between the negative
supply and the common emitters of the NPN drivers or common
sources of N-Channel FET drivers. This point is connected to one
end of a potentiometer (e.g. 100k ohms), the other end of which is
connected to the positive supply. The wiper pick-off is adjusted so
that all outputs are disabled for currents greater than the limit. The
action of the input is to disable all external output drivers. When
BRAKE exists, OVER-CURRENT SENSE will be over-ridden. The
over-current circuitry latches the over-current condition. The latch
may be reset by the positive edge of either the saw-tooth
OSCILLATOR or the ENABLE input. When using the ENABLE
input as a chopped input, the OSCILLATOR input should be held
at V
must be used to reset the over-current latch.
VTRIP (Pin 13)
This input is used in conjunction with the saw-tooth OSCILLATOR
input. When the voltage level applied to VTRIP is more negative
than the waveform at the OSCILLATOR input, the outputs will be
enabled as shown in Table 3. When VTRIP is more positive than
the saw-tooth OSCILLATOR waveform the external output drivers
are disabled. The saw-tooth waveform at the OSCILLATOR input
typically varies from (0.4*V
VTRIP input in conjunction with the OSCILLATOR is to provide
variable speed adjustment for the motor by means of PWM for
VSS greater than 7V. Below VSS = 7V, the IC may only be used
as a commutator. (See Note).
Note: Below VSS = 7V, the OSCILLATOR saw-tooth amplitude is
too small to allow proper operation of the PWM circuitry.
OSCILLATOR (Pin 14)
R and C connected to this input (See Figure 6) provide the timing
components for a saw-tooth OSCILLATOR. The signal generated
is used in conjunction with VTRIP to provide PWM for variable
speed applications and to reset the over-current condition.
OUTPUTS 1,2,3 (Pins 2,3,4)
These open drain outputs are enabled as shown in Table 2 and
provide base current to PNP transistors when COMMON is
floating or gate drive to P-channel FET drivers when COMMON is
tied to VSS.
OUTPUTS 4,5,6 (Pins 6,7,8)
These open drain outputs are enabled in Table 2 and provide
base current to NPN transistors when COMMON is floating or
gate drive to N-Channel FET drivers when COMMON is tied to
VSS.
COMMON (Pin 5)
The COMMON is connected to VSS when using P-Channel and
N-Channel drivers (Figure 1). Pin 5 is left floating when using
PNP and NPN transistors (Figure 2).
7262-051711-2
SS
. When the ENABLE input is held high, the OSCILLATOR
SS)
to (V
SS
- 2V). The purpose of the
VSS, VDD (Pins 11, 18)
Supply voltage positive and negative terminals.
TYPICAL CIRCUIT OPERATION:
The oscillator is used for motor speed control as explained under
VTRIP. Both upper and lower motor drive transistors are pulse
width modulated (see Fig.1 or 2) during speed control. The
outputs turn on in pairs (See Table 3). For example, in Figure 2,
(see dotted line, Fig.2) Q8 and Q4 are on, thus enabling a path
from the positive supply through Q101, Q8, Q4, R5 and the
emitter-base junction of Q105 and the fractional-ohm resistor to
ground. The current in the above described path is determined by
the power supply voltage, the voltage across the base-emitter
junctions of Q101 and Q105 (1.4V for single transistor or 2.8V for
Darlington pairs), the impedance of Q8 and Q4 and the value of
R5. Table 1 provides the recommended value for R5. R4 and R6
are the same value.
In Figure 1, the common (Pin 5) is tied to VSS, the outputs still
turn on in pairs. By adding external buffers (U1) for outputs O1,
O2 and O3 the same sequence of motor winding conduction
occurs as is the case for Figure 2. For example when Q8 and Q4
turn on, transistor Q101 and Q105 turn on which is the same as in
Figure 2. The other external output pairs turn on similarly and the
commutation sequence is identical to that of Figure 2 (as shown
in Table 3).