ls7260 LSI Computer Systems, Inc., ls7260 Datasheet - Page 3

• Manufacturer Part Number: ls7260
• Description: Brushless Dc Motor Commutator/controller
• Manufacturer: LSI Computer Systems, Inc.

7260-012703-3
*
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.
For the LS7262, the outputs turn on in pairs (See Table 3). For
example (see dotted line, Fig. 2): Q8 and Q4 are on, thus ena-
bling a path from the positive supply through the emitter-base
junction of Q101, Q8, Q4, R5, the base emitter 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 drops across the base-emitter junctions of
Q101 and Q105 (1.4V for single transistor or 2.8V for Darling-
ton 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.
(VOLTS)
See Figures 1 and 2.
For the LS7260,
Outputs O1,O2,O3 are
the logical inversions of
the corresponding Out-
puts of the LS7262.
Oscillator:
Frequency Range
External Resistor Range
NOTE: Theoretical switching point of the OVERCURRENT SENSE input is one half of the power supply determined by an internal bias
network in manufacturing. Tolerances cause the switching point to vary plus or minus 0.25V. After manufacture, the switching point
remains fixed within 10mV over time and temperature. The input switching sensivity is a maximum of 50mV. There is no hysteresis on
the OVERCURRENT SENSE input.
SUPPLY
SEQUENCE SELECT
ELECTRICAL SEPARATION
SENSE INPUTS
The OVERCURRENT input (BRAKE low) enables external output drivers in normal sequence when more negative than Vss/2 and disables
all external output drivers when more positive than Vss/2. The OVERCURRENT is sensed continuously, and sets a flip flop which is reset
by the rising edge of the ENABLE input or the sawtooth OSCILLATOR. (See description under OVERCURRENT SENSE.)
The VTRIP Input (BRAKE low) enables the outputs in normal sequence when more negative than the OSC input and disables all outputs
when more positive than the OSC input. The VTRIP input may be disabled by connecting it to V
(See description under VTRIP)
POWER
12
15
18
21
24
28
OUTPUT CURRENT LIMITING RESISTOR SELECTION TABLE
6
9
**exceeds max current possible for this voltage
*causes excessive power dissipation
.20 .33 .62 .91 1.5
.36 .56 .91 1.3 2.2
20
**
**
*
*
*
*
.75 1.2 1.6 2.7
15
**
**
*
*
*
OUTPUT CURRENT
TABLE 3. OUTPUT COMMUTATION SEQUENCE FOR THREE PHASE OPERATION
CS1 CS2
S1 S2 S3
1.5 2.0 3.3
1.8 2.3 3.6
10
0 0 0
1 0 0
1 1 0
1 1 1
0 1 1
0 0 1
0 1 0
1 0 1
**
**
0
*
TABLE 1
(- 60°-)
.43 .86
2.7 4.3
7.5
**
0
**
5
CS1 CS2
S1 S2 S3
0 0 1
1 0 1
1 0 0
1 1 0
0 1 0
0 1 1
0 0 0
1 1 1
(- 120°-)
0
2.5
.24
2.2
3.3
4.3 Resistance
5.1
6.2
7.5
9.1
1
mA
R
F
(k )
osc
osc
CS1 CS2 CS1 CS2
S1 S2 S3
0 1 0
1 1 0
1 0 0
1 0 1
0 0 1
0 1 1
0 0 0
1 1 1
(- 240°-)
1
0
(- 300°-)
S1 S2 S3 ENABLED A
0 1 1
1
1 1 1
1 1 0
1 0 0
0 0 0
0 0 1
0 1 0
1 0 1
22
0
For the LS7260, (See Fig. 1) the external drivers also
turn on in pairs. Internal operation is somewhat different
than the LS7262. For example, external transistors Q101
and Q105 will turn on when internal transistor Q8 turns
off and Q4 turns on enabling full power supply drive on
Q101 and Q105. Since Pin 5 is tied to V
channel Driver Q101 is brought to ground by R1 and the
Gate of N-Channel driver Q105 is brought to V
Other external output pairs turn on similarly and the com-
mutation sequence is identical to that of the LS7262
(Table 3). Table 2 indicates the minimum value of
R1 (= R2 = R3 = R4 = R5 = R6) needed as a function of
output drive voltage for Fig. 1.
1
OUTPUTS
O1, O5
O3, O5
O3, O4
O2, O4
O2, O6
O1, O6
R1 (k ohms)
ALL DISABLED
ALL DISABLED
FWD/REV = 1
10
1/RC
4.0
1.5
-
*
For Power Supply 5V - 28V
+
Off
Off
-
-
+
DRIVERS
DD
B
-
Off
Off
-
+
+
and the OSC input to V
TABLE 2
Off
C
+
+
Off O1, O5
*
-
-
1000
100
OUTPUTS
ENABLED
O2, O4
O2, O6
O1, O6
O3, O5
O3, O4
Output Voltage
Vss - 0.5
Vss - 1.0
Vss - 2.0
FWD/REV = 0
ALL DISABLED
ALL DISABLED
SS
kHz
k
, the gate of P-
*
SS
A
-
Off
+
+
Off
-
.
DRIVERS
SS
by Q4.
Off
Off
B
+
+
-
-
Off
Off
*
C
-
-
+
+