BRUSHLESS DC MOTOR COMMUTATOR/CONTROLLER

FEATURES:
·

Direct drive of P-Channel and N-Channel FETs (LS7260)

Direct drive of PNP and NPN transistors (LS7262)

Six outputs drive power switching bridge directly

Open or closed loop motor speed control.

+5V to +28V operation (Vss - V

Externally selectable input to output code for 60°,

120°, 240°, or 300° electrical sensor spacing.

Three or four phase operation

Analog Speed control

Direction control

Output Enable control

Positive Static Braking

Overcurrent Sensing

LS7260, LS7262 (DIP); LS7260-S, LS7262-S (SOIC);

LS7260-TS, LS7262-TS (TSSOP) - See Connection Diag.

DESCRIPTION:

The LS7260/LS7262 are MOS integrated circuits de-
signed to generate the signals necessary to control a
three phase or four phase brushless DC motor. They
are the basic building blocks of a brushless DC motor
controller. The circuits respond to changes at the
SENSE inputs, originating at the motor position sensors,
to provide electronic commutation of the motor wind-
ings. Pulse Width Modulation of outputs for motor speed
control is accomplished through either the ENABLE in-
put or through the Analog input (V TRIP) in conjunction
with the OSCILLATOR input. Overcurrent circuitry is
provided to protect the windings, associated drivers and
power supply. The overcurrent circuitry causes the ex-
ternal output drivers to switch off immediately upon
sensing the overcurrent condition and on again only
when the overcurrent condition disappears and the pos-
itive edge of either the ENABLE input or the sawtooth
OSCILLATOR occurs. This limits the overcurrent sense
cycling to the chopping rate of the ENABLE input or the
sawtooth OSCILLATOR.

A positive braking feature is provided to effect rapid de-
celeration. While the LS7262 is designed for driving
NPN and PNP transistors (See Fig. 2), the LS7260 is
designed to drive both NMOS and PMOS Power FETs
and develops a full 12V drive for both the N-Channel
and P-Channel devices (See Fig. 1) when using a 12V
power supply.

LSI

CS1

OUT 1

OUT 2

OUT 3

OUT 4

COMMON

OUT 5

OUT 6

BRAKE

E N A B L E

CS2

F W D / R E V

(-V)

OSCILLATOR

V TRIP

O V E R C U R R E N T S E N S E

(+V)

CONNECTION DIAGRAM - TOP VIEW

INPUT/OUTPUT DESCRIPTION:
COMMUTATION SELECTS (Pins 1, 20)
These inputs are used to select the proper sequence of outputs
based on the electrical separation of the motor position sensors.
See Table 3. Note that in all cases the external output drivers
are disabled for invalid SENSE input codes. Internal pull down
resistors are provided at Pins 1 and 20 causing a logic zero
when these pins are left open.

FORWARD/REVERSE (Pin 19)
This input is used to select the proper sequence of Outputs for
the desired direction of rotation for the Motor (See Table 3). An
internal pull-up resistor holds the input high when left open.

SENSE INPUTS (Pins 15, 16, 17)
These inputs provide control of the output commutation
sequence as shown in Table 3. S1, S2, S3 originate in the posi-
tion sensors of the motor and must sequence in cycle code or-
der. Hall Switch pull-up resistors are provided at Pins 15, 16 and
17. The positive supply of the Hall devices should be common
to the chip Vss.

BRAKE (Pin 9)
For the LS7262, a high level at this input unconditionally turns
Off Outputs 1, 2 and 3 and turns On Outputs 4, 5 and 6 (See
Fig. 2). For the LS7260, a high level at this input turns On Out-
puts 1, 2 and 3 and Outputs 4, 5 and 6 (See Fig. 1). In both
cases, transistors Q101, Q102 and Q103 cut off and transistors
Q104, Q105 and Q106 turn on, shorting the windings together,
The BRAKE has priority over all other inputs.

January 2003

7260-012703-1

LSI/CSI

LSI Computer Systems, Inc. 1235 Walt Whitman Road, Melville, NY 11747 (631) 271-0400 FAX (631) 271-0405

LS7260
LS7262

A3800

BRAKE (Pin 9) (Cont'd)
An internal pull-down resistor holds the input low when left
open. (Center- tapped motor configuration requires a power
supply disconnect transistor controlled by the BRAKE signal
- See Figure 2A).

ENABLE (Pin 10)
A high level at this input permits the output to sequence as
in Table 3, while a low disables all external output drivers.
An internal pull-up resistor holds the input high when left
open. Positive edges at this input will reset the overcurrent
flip-flop.

OVERCURRENT SENSE (Pin 12)
This input provides the user a way of protecting the motor
winding, drivers and power supply from an overload condi-
tion. 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 pickoff 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, OVERCURRENT SENSE will be overridden. The
overcurrent circuitry latches the overcurrent 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 OSC input should be
held at V

. When the ENABLE input is held high, the OSC-

must be used to reset the overcurrent latch.

VTRIP (Pin 13)
This input is used in conjunction with the sawtooth OSC in-
put. When the voltage level applied to VTRIP is more neg-
ative than the waveform at the OSC input, the Outputs will
be enabled as shown in Table 3. When VTRIP is more pos-
itive than the sawtooth OSCILLATOR waveform the external
output drivers are disabled.

The sawtooth waveform at the OSC input typically varies
from 0.4Vss to Vss - 2V. The purpose of the VTRIP input
in conjunction with the OSCILLATOR is to provide variable
speed adjustment for the motor by means of PWM.

OSCILLATOR (Pin 14)
An R and C connected to this input (see Figure 6) provide
the timing components for a sawtooth OSCILLATOR. The
signal generated is used in conjunction with VTRIP to pro-
vide PWM for variable speed applications and to reset the
overcurrent condition.

OUTPUTS 1, 2, 3 (Pins 2, 3, 4)
For the LS7262, these open drain Outputs are enabled as
shown in Table 2 and provide base current to PNP tran-
sistors or gate drive to P-Channel FET drivers when COM-
MON is floating. If COMMON is held at Vss, these Outputs
can provide drive to NPN transistors or N-Channel FET
drivers. For the LS7260, these Outputs provide drive to
P-Channel FET drivers if COMMON is held at V

OUTPUTS 4, 5, 6 (Pins 6, 7, 8)
These open drain Outputs are enabled as in Table 2 and
provide base current to NPN transistors or gate drive to
N-Channel FET drivers.

COMMON (Pin 5)
The COMMON may be connected to Vss when using a
center-tapped motor configuration or when using all NPN
or N-Channel drivers. For the LS7260, the COMMON is
tied to V

Vss (Pin 11)
Supply voltage positive terminal.

(Pin 18)

Supply voltage negative terminal (ground).

MAXIMUM RATINGS:

PARAMETER

SYMBOL

VALUE UNIT

DC Supply Voltage

Vss - V

+35

Any Input Voltage to Vss

-30 to +0.5

Storage Temperature

STG

-65 to +150

°C

Operating Temperature

-40 to +125

°C

DC ELECTRICAL CHARACTERISTICS:
(All Voltages Referenced to V

= 25°C unless otherwise specified)

SYMBOL

MIN

TYP

MAX

UNIT

Supply Voltage

Supply Current (Outputs not loaded)

4.5

7260-012703-2

Input Specifications:
BRAKE, ENABLE, CS1, CS2

150

S1, S2, S3, FWD/REV
Voltage (Logic 1)

1.5

(Logic 0)

- 4.0

OVERCURRENT SENSE (See Note)
Threshold Voltage

/2) - 0.25

SS/

2) + 0.25 V

TABLE 1

OUTPUT CURRENT LIMITING RESISTOR SELECTION TABLE

POWER

OUTPUT CURRENT

SUPPLY
(VOLTS) 20 15 10 7.5 5 2.5 mA

.24

.43 .86

2.2

.20 .33 .62 .91 1.5

3.3

.36 .56 .91 1.3 2.2

4.3 Resistance

.75 1.2 1.6 2.7

5.1 (k

)

1.5 2.0 3.3

6.2

1.8 2.3 3.6

7.5

2.7 4.3

9.1

*causes excessive power dissipation
**exceeds max current possible for this voltage

TABLE 2

For Power Supply 5V - 28V

R1 (k ohms) Output Voltage

10 Vss - 0.5
4.0 Vss - 1.0
1.5 Vss - 2.0

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.

7260-012703-3

Oscillator:
Frequency Range

osc

1/RC

100

kHz

External Resistor Range

osc

1000

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.

TABLE 3. OUTPUT COMMUTATION SEQUENCE FOR THREE PHASE OPERATION

SEQUENCE SELECT

CS1 CS2

CS1 CS2 CS1 CS2

FWD/REV = 1

FWD/REV = 0

0 0 0 1 1 0 1 1

ELECTRICAL SEPARATION (- 60°-)

(- 120°-)

(- 240°-) (- 300°-)

OUTPUTS DRIVERS

SENSE INPUTS

S1 S2 S3

S1 S2 S3 S1 S2 S3

ENABLED A B C ENABLED A B C

0 0 0

0 0 1

0 1 0 0 1 1

O1, O5

+ - Off

O2, O4

- + Off

1 0 0

1 0 1

1 1 0

1 1 1

O3, O5

Off - +

O2, O6

Off + -

1 1 0

1 0 0

1 1 0

O3, O4

- Off +

O1, O6

+ Off -

1 1 1

1 1 0

1 0 1

1 0 0

O2, O4 - + Off

O1, O5

+ - Off

0 1 1

0 1 0

0 0 1 0 0 0

O2, O6

Off + -

O3, O5

Off - +

0 0 1

0 1 1

0 0 1

O1, O6

+ Off -

O3, O4

- Off +

0 1 0

0 0 0

0 1 0 ALL DISABLED

ALL DISABLED

1 0 1

1 1 1

1 0 1

ALL DISABLED

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

and the OSC input to V

(See description under VTRIP)

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

, the gate of P-

channel Driver Q101 is brought to ground by R1 and the
Gate of N-Channel driver Q105 is brought to V

by Q4.

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.

See Figures 1 and 2.
For the LS7260,
Outputs O1,O2,O3 are
the logical inversions of
the corresponding Out-
puts of the LS7262.

TABLE 4. OUTPUT COMMUTATION SEQUENCE FOR FOUR PHASE OPERATION

CS1 = CS2 = 0 OUTPUTS ENABLED

S2,S3

FWD/REV = 1

FWD/REV = 0

7260-012703-5

BRAKE

M O T O R
S U P P L Y

Vss

COMMON

BRAKE

INPUT

L S 7 2 6 2

FORWARD

R E V E R S E

I N 9 1 4

2 . 2 K

Inputs from SG1731
o r U C 1 6 3 7

F/R

E N A B L E

I N 9 1 4

L S 7 2 6 0
or
L S 7 2 6 2

FIGURE 3. PRECISION CONTROL BRUSHLESS DC MOTOR DRIVE

FIGURE 2A.

SINGLE-ENDED

DRIVER CIRCUIT

This configuration requires only
one base current limiting resistor
connected from the COMMON
pin to Vss.

For controlled acceleration and deceleration of motors in
the forward or reverse directions, a motor control pulse
width modulator circuit such as the SG1731 or UC1637
can be interfaced with the LS7260 or LS7262.

The logical OR gate made up of the resistor-diode net-
work permits the LS7260 or LS7262 to be enabled when
either the forward or reverse input is high. By applying

the forward input directly to Pin 19, the motor can only
operate in the forward direction when the forward input is
high and only in the reverse direction when the reverse
input is high. Motor direction is determined by relative
pulse widths of the forward and reverse inputs while ac-
celeration or deceleration is determined by variations of
these widths.

For four phase commutation (See Fig. 4), the COMMUTA-
TION SELECT inputs must both be tied low. The S1 input
is driven from one motor position sensor while the S2 and
S3 inputs are connected together and driven by the
second position sensor. The COMMON input must be

connected to Vss. The sensors have an electrical separa-
tion of 90°. Figure 4A indicates the use of Bipolar Tran-
sistors. Figure 4B indicates the use of FETs. In both
cases, the LS7262 is used.

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