Dwg. PP-040B

ABSOLUTE MAXIMUM RATINGS

at T

= +25

Load Supply Voltage, V

. . . . . . . . . . 14 V

Output Current, I

OUT

. . . . . . . . . . . .

1.25 A

Logic Supply Voltage, V

. . . . . . . . . 6.0 V

Logic Input Voltage Range,

. . . . . . . . . . . -0.3 V to V

+ 0.3 V

Package Power Dissipation, P

See Graph

Operating Temperature Range,

. . . . . . . . . . . . . . . . . . 0

C to +70

Junction Temperature, T

. . . . . . . +150

Storage Temperature Range,

. . . . . . . . . . . . . . . -55

C to +150

Fault conditions that produce excessive junction
temperature will activate device thermal shutdown
circuitry. These conditions can be tolerated, but
should be avoided.

Output current rating may be restricted to a value
determined by system concerns and factors.
These include: system duty cycle and timing,
ambient temperature, and use of any heatsinking
and/or forced cooling. For reliable operation, the
specified maximum junction temperature should
not be exceeded.

Always order by complete part number, e.g., A8906CLB .

Data Sheet

26301.4

The A8906CLB is a bidirectional three-phase brushless dc motor

controller/driver. The three half-bridge outputs are low on-resistance n-
channel DMOS devices capable of driving up to 1 A. The A8906CLB
provides complete, reliable, self-contained back-EMF sensing motor
startup and running algorithms. A programmable digital frequency-
locked loop speed control circuit together with the linear current control
circuitry provides precise motor speed regulation.

A serial port allows the user to program various features and

modes of operation, such as the speed control parameters, rotational
direction, startup current limit, sleep mode, diagnostic modes, and
others.

The A8906CLB is fabricated in Allegro's BCD (Bipolar CMOS

DMOS) process, an advanced mixed-signal technology that combines
bipolar, analog and digital CMOS, and DMOS power devices. The
A8906CLB is provided in a 24-lead wide-body SOIC batwing package.
It provides for the smallest possible construction in surface-mount
applications.

FEATURES

DMOS Outputs

Low

DS(on)

Startup Commutation Circuitry

Back-EMF Commutation Circuitry

Direction Control

Serial Port Interface

Frequency-Locked Loop Speed Control

Sector Data Tachometer Signal Input

Programmable Start-Up Current

Diagnostics Mode

Sleep Mode

Linear Current Control

Internal Current Sensing

Dynamic Braking Through Serial Port

Power-Down Dynamic Braking

System Diagnostics Data Out

Data Out Ported in Real Time

Internal Thermal Shutdown Circuitry

BIDIRECTIONAL 3-PHASE BRUSHLESS DC MOTOR

CONTROLLER/DRIVER WITH BACK-EMF SENSING

BRAKE

FILTER

DATA IN

LOGIC
SUPPLY

GROUND

CHIP SELECT

CLOCK

RESET

GROUND

OUTA

OUTB

OUTC

C D1

LOAD

SUPPLY

C WD

C D2

DATA OUT

SECTOR
DATA

CENTERTAP

OSCILLATOR

C RES

SERIAL PORT

FLL

MUX

COMMUTATION

DELAY

BOOST

CHARGE

PUMP

8906

PRELIMINARY INFORMATION

(Subject to change without notice)

March 1, 1999

8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

FUNCTIONAL BLOCK DIAGRAM

CURRENT
CONTROL

Dwg. FP-034

CENTERTAP

C WD

OSC

SECTOR

DATA

FILTER

C ST

C RES

BRAKE

OUT A

OUT B

OUTC

COMMUTATION

LOGIC

COMMUTATION

DELAY

C D1

C D2

WATCHDOG

TIMER

SEQUENCE

LOGIC

BLANK

FCOM

OUT A

OUT B

OUTC

LOAD
SUPPLY

CHARGE

PUMP

FREQUENCY-

LOCKED LOOP

SERIAL PORT

MUX

CLOCK

DATA IN

DATA

OUT

CHIP

SELECT

RESET

TSD

LOGIC

SUPPLY

START-UP

OSC.

BOOST

CHARGE

PUMP

BRAKE

18-19

6-7

GROUND

100

125

150

2.5

1.5

1.0

0.5

TEMPERATURE in

2.0

Dwg. GP-019B

R = 6

C/W

R = 55

C/W

ALLOWABLE PACKAGE POWER DISSIPATION in WATTS

8906

BIDIRECTIONAL

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

ELECTRICAL CHARACTERISTICS at T

= +25

C, V

= 5.0 V

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Logic Supply Voltage

Operating

4.5

5.0

5.5

Logic Supply Current

Operating

7.5

Sleep Mode

250

500

Load Supply Voltage

Operating

4.0

Thermal Shutdown

165

Thermal Shutdown Hysteresis

Output Drivers

Output Leakage Current

DSX

= 14 V, V

OUT

= 14 V

1.0

300

= 14 V, V

OUT

= 0 V

-1.0

-300

Total Output ON Resistance

DS(on)

OUT

= 600 mA

1.0

1.4

Output Sustaining Voltage

DS(sus)

= 14 V, I

OUT

= I

OUT

(MAX), L = 3 mH

Clamp Diode Forward Voltage

= 1.0 A

1.25

1.5

Control Logic

Logic Input Voltage

IN(0)

SECTOR DATA, RESET, CLK,

-0.3

1.5

IN(1)

CHIP SELECT, OSC

3.5

5.3

Logic Input Current

IN(0)

= 0 V

-0.5

IN(1)

= 5.0 V

1.0

DATA Output Voltage

OUT(0)

OUT

= 500

1.5

OUT(1)

OUT

= -500

3.5

Current

CST

Charging

-9.0

-10

-11

Discharging

500

Threshold

CSTH

2.25

2.5

2.75

CSTL

0.85

1.0

1.15

Filter Current

FILTER

Charging

-9.0

-10

-11

Discharging

9.0

Leakage, V

FILTER

= 2.5 V

5.0

Filter Threshold

FILTERTH

1.57

1.85

2.13

Current

Charging

-18

-20

-22

Discharging

Current Matching

CD(DISCHRG)

CD(CHRG)

1.8

2.0

2.2

Threshold

CDTH

2.25

2.5

2.75

Continued next page ...

(Source + Sink + R

)

or C

)

8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

SERIAL PORT TIMING CONDITIONS

Limits

Characteristic

Symbol

Test Conditions

Min.

Typ.

Max.

Units

Current

CWD

Charging

-9.0

-10

-11

Threshold Voltage

0.22

0.25

0.28

2.25

2.5

2.75

Max. FLL Oscillator Frequency

OSC

= 5.0 V, T

= 25

MHz

OUT

(MAX)

D3 = 0, D4 = 0

1.0

1.2

1.4

D3 = 0, D4 = 1

0.9

1.0

1.1

D3 = 1, D4 = 0

0.5

0.6

0.7

D3 = 1, D4 = 1

250

BRAKE Threshold

BRK

1.5

1.75

2.0

BRAKE Hysteresis Current

BRKL

BRK

= 750 mV

Transconductance Gain

0.42

0.50

0.58

A/V

Centertap Resistors

5.0

Back-EMF Hysteresis

BEMF

- V

CTAP

5.0

FCOM Transition

-5.0

-20

-37

ELECTRICAL CHARACTERISTICS continued

DATA

CLOCK

Dwg. WP-019

CHIP SELECT

Minimum CHIP SELECT setup time before CLOCK rising edge .......... 100 ns

Minimum CHIP SELECT hold time after CLOCK rising edge ............... 150 ns

Minimum DATA setup time before CLOCK rising edge ........................ 150 ns

Minimum DATA hold time after CLOCK rising edge ............................. 150 ns

Minimum CLOCK low time before CHIP SELECT .................................. 50 ns

Maximum CLOCK frequency .............................................................. 3.3 MHz

8906

BIDIRECTIONAL

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

TERMINAL FUNCTIONS

Term.

Terminal Name

Function

LOAD SUPPLY

; the 5 V or 12 V motor supply.

One of two capacitors used to generate the ideal commutation points from the
back-EMF zero crossing points.

Timing capacitor used by the watchdog circuit to disable the back-EMF compara-
tors during commutation transients, and to detect incorrect motor position.

Startup oscillator timing capacitor.

OUT

Power amplifier A output to motor.

6-7

GROUND

Power and logic ground and thermal heat sink.

OUT

Power amplifier B output to motor.

OUT

Power amplifier C output to motor.

CENTERTAP

Motor centertap connection for back-EMF detection circuitry.

BRAKE

Active low turns ON all three sink drivers shorting the motor windings to ground.
External capacitor and resistor at B

RAKE

provide brake delay.

RES

External reservoir capacitor used to hold charge to drive the source drivers'
gates. Also provides power for brake circuit.

FILTER

Analog voltage input to control motor current. Also, compensation node for
internal speed control loop.

SECTOR DATA

External tachometer input. Can use sector or index pulses from disk to provide
precise motor speed feedback to internal frequency-locked loop.

LOGIC SUPPLY

; the 5 V logic supply.

OSCILLATOR

Clock input for the speed reference counter. Typical max. frequency is 10 MHz.

DATA OUT

Thermal shutdown indicator, FCOM, TACH, or SYNC signals available in real
time, controlled by 2-bit multiplexer in serial port.

18-19

GROUND

Power and logic ground and thermal heat sink.

RESET

When pulled low forces the chip into sleep mode; clears all serial port bits.

CHIP SELECT

Strobe input (active low) for data word.

CLOCK

Clock input for serial port.

DATA IN

Sequential data input for the serial port.

One of two capacitors used to generate the ideal commutation points from the
back-EMF zero crossing points.

8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

(output crossing through centertap). True back-EMF zero crossings are
used by the adaptive commutation delay circuit to advance the state
sequencer (commutate) at the proper time to synchronously run the
motor. Back-EMF zero crossings are indicated by FCOM, an internal
signal that toggles at every zero crossing. FCOM is available at the
DATA OUT terminal via the programmable data out multiplexer.

Direction Control. Serial port bit D2 controls the direction of

rotation (see sequencer state table). The motor should be at a com-
plete stop before beginning a startup sequence that reverses the
direction of rotation.

Startup Oscillator. If the motor does not move at the initial startup

state, then it is in a null-torque position. In this case, the outputs are
commutated automatically by the startup oscillator after a period set by
the external capacitor at C

where

CST

In the next state, the motor will move, back EMF will be detected,

and the motor will accelerate synchronously. Once normal synchro-
nous back-EMF commutation occurs, the startup oscillator is defeated
by pulses of pulldown current at C

at each commutation, which

prevents C

from reaching its upper threshold and thus completing a

cycle and commutating.

Power Outputs. The power outputs of

the A8906CLB are n-channel DMOS transis-
tors with a total source plus sink r

DS(on)

typically 1

. Internal charge pump boost

circuitry provides voltage above supply for
driving the high-side DMOS gates. Intrinsic
ground clamp and flyback diodes provide
protection when switching inductive loads and
may be used to rectify motor back-EMF in
power-down conditions. An external Schottky
power diode or pass FET is required in series
with the load supply to allow motor back-EMF
rectification in power down conditions.

Back-EMF Sensing Motor Startup and

Running Algorithm. The A8906CLB pro-
vides a complete self-contained back-EMF
sensing startup and running commutation
scheme. The three half-bridge outputs are
controlled by a state machine. There are six
possible combinations. In each state, one
output is high (sourcing current), one low
(sinking current), and one is OFF (high
impedance or `Z'). Motor back EMF is sensed
at the OFF output. The truth table for the
output drivers sequencing is:

Direction

Control

OUT

High

Low

High

Low

High

Low

High

Low

High

Low

At startup, the outputs are enabled in one

of the sequencer states shown. The back
EMF is examined at the OFF output by
comparing the output voltage to the motor
centertap voltage at CENTERTAP. The
motor will then either step forward, step
backward, or remain stationary (if in a null-
torque position). If the motor moves, the
back-EMF detection circuit waits for the
correct polarity back-EMF zero crossing

FUNCTIONAL DESCRIPTION

Dwg. WP-016-1

FCOM

FCOM TOGGLES AT
BACK-EMF ZERO CROSSING

SOURCE ON

SINK ON

BACK-EMF VOLTAGE

OUTA

OUTB

OUTC

CTAP

4(V

CSTH

- V

CSTL

) x C

ST(charge)

+ I

ST(discharge)

D2 Low

D2 High

8906

BIDIRECTIONAL

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

Blanking and Watchdog Timing Functions. The blanking and

watchdog timing functions are derived from one timing capacitor, C

where

BLANK

and

The CWD capacitor begins charging at each commutation, initiating

the BLANK signal. BLANK is an internal signal that inhibits the back-
EMF comparators during the commutation transients, preventing errors
due to inductive recovery and voltage settling transients.

The watchdog timing function allows time to detect correct motor

position by checking the back-EMF polarity after each commutation. If
the correct polarity is not observed between t

BLANK

and t

, then the

watchdog timer commutates the outputs to the next state to synchro-
nize the motor. This function is useful in preventing excessive reverse
rotation, and helps in resynchronizing (or starting) with a moving
spindle.

Adaptive Commutation Delay. The

adaptive commutation delay circuit uses the
back-EMF zero-crossing indicator signal
(FCOM) to determine an optimal commuta-
tion time for efficient synchronous operation.
This circuit commutates the outputs, delayed
from the last zero crossing, using two
external timing capacitors, C

and C

to measure the time between crossings.

where t

= t

FCOM

charges up with a fixed current from

its 2.5 V reference while FCOM is high.
When FCOM goes low at the next zero
crossing, C

is discharged at approximately

twice the charging current. When CD

reaches the CD threshold, a commutation
occurs. C

operates similarly except on the

opposite phase of FCOM . Thus the com-
mutations occur approximately halfway
between zero crossings. The actual delay is
slightly less than halfway to compensate for
electrical delays in the motor, which im-
proves efficiency.

Dwg. WP-016-2

FCOM

t FCOM

t CD1

VCWD

CD1

VCD2

t CD2

WATCHDOG-TRIGGERED

COMMUTATION

BLANK

Dwg. WP-022

BLANK

CWD

NORMAL COMMUTATION

BLANK

Dwg. WP-021

BLANK

CWD

CD(charge)

CD(discharge)

x C

CWD

x C

CWD

8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

Dwg. EP-045

SECTOR

FCOM

TACH

D5D18

D19

D20 &
D21

OSC

REF

4-BIT

FIXED

COUNTER

14-BIT

PROGRAMMABLE

COUNTER

SERIAL PORT

COUNT

(3 x MOTOR POLES)

MUX

REF

TACH

ERROR

FAST

ONCE-AROUND

PULSE

REF

TACH

ERROR

SLOW

Speed Control. The A8906CLB includes a frequency-locked loop

speed control system. This system monitors motor speed via internal
or external digital tachometer signals, generates a precision speed
reference, determines the digital speed error, and corrects the motor
current via an internal charge pump and external filtering components
on the FILTER terminal.

A once per revolution TACH signal can be generated by counting

cycles of FCOM (the number of motor poles must be selected via the
serial port). TACH is then a jitter-free signal that toggles once per
motor revolution. The rising edge of TACH triggers REF, a precision
speed reference derived by a programmable counter. The duration of
REF is set by programming the counter to count the desired number of
OSC cycles

YANK

SPEED-CONTROL

INITIALIZATION

POWER UP

ERROR FAST

FROM FLL

S Q

FILTER

ERROR SLOW

FROM FLL

CHARGE

PUMP

ERROR FAST
FROM FLL

Dwg. EP-046

OUT

SEQUENTIAL

LOGIC

RES

BOOST

CHARGE

PUMP

MUX

LINEAR
CURRENT CONTROL

FROM
SERIAL PORT
REGISTER
D3 AND D4

MAX CURRENT LIMIT

V max

1.85 V

Current Control. The A8906CLB provides linear current control

via the FILTER terminal, an analog voltage input. Maximum current
limit is also provided, and is controlled in four steps via the serial port.
Output current is sensed via an internal sense resistor (R

). The

voltage across the sense resistor is compared to one-tenth the voltage
at the FILTER terminal less the filter threshold voltage, or to the maxi-
mum current limit reference, whichever is lower. This transcon-
ductance function is I

OUT

= (V

FILTER

-V

FILTERTH

) / 10R

, where R

nominally 0.2

and V

FILTERTH

is approximately 1.85 V.

desired

total count

where the total count (number of oscillator
cycles) is equal to the sum of the selected
(programmed low) count numbers corre-
sponding to bits D5 through D18.

The speed error is detected as the

difference in falling edges of TACH and
REF. The speed error signals control the
error-correcting charge pump on the FILTER
terminal, which drive the external loop com-
pensation components to correct the motor
current.

Sector Mode. An external tachometer

signal, such as sector or index pulses, may
be used to create the TACH signal, rather
than the internally derived once around. To
use this mode, the signal is input to the
SECTOR terminal, and the sector mode must
be enabled via the serial port. When Switch-
ing from the once-around mode to sector
mode, it is important to monitor the SYNC
signal on DATA OUT, and switch modes only
when SYNC is low. This ensures making the
transition without disturbing the speed control
loop. The speed reference counter should be
reprogrammed at the same time.

Speed Loop Initialization (YANK). To

improve the acquire time of the speed control
loop, there is an automatic feature controlled
by an internal YANK signal. The motor is
started at the maximized programmed current
by bypassing the FILTER terminal. The
FILTER terminal is clamped to an internal
reference (the filter threshold voltage),
initializing it near the closed loop operating
point. YANK is enabled at startup and stays
high until the desired speed is reached. Once
the first error-fast occurs, indicating the motor
crossed through the desired speed, YANK
goes low. This releases the clamp on the
FILTER terminal and current control is
returned to FILTER. This feature optimizes
speed acquire and minimizes settling. The
Current Control Block Diagram illustrates the
YANK signal and its effects.

60 x f

OSC

desired motor speed (rpm)

8906

BIDIRECTIONAL

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

Serial Port. The serial port functions to write various operational

and diagnostic modes to the A8906CLB. The serial port DATA IN is
enabled/disabled by the CHIP SELECT terminal. When CHIP SE-
LECT is high the serial port is disabled and the chip is not affected by
changes in data at the DATA IN or CLOCK terminals.

To write data to the serial port, the CLOCK terminal should be low

prior to the CHIP SELECT terminal going low. Once CHIP SELECT
goes low, information on the DATA IN terminal is read into the shift
register on the positive-going transition of the CLOCK. There are 24
bits in the serial input port.

Data written into the serial port is latched and becomes active

upon the low-to-high transition of the CHIP SELECT terminal at the
end of the write cycle. D0 will be the last bit written to the serial port.

SERIAL PORT BIT DEFINITIONS

D0- Sleep/Run Mode; LOW = Sleep, HIGH = Run

This bit allows the device to be powered down when not in use.

D1- Step Mode; LOW = Normal Operation, HIGH = Step Only

When in the step-only mode the back-EMF commutation circuitry
is disabled and the power outputs are commutated by the start-
up oscillator. This mode is intended for device and system
testing.

D2- Direction; LOW = Forward, HIGH = Reverse.

D3 and D4 - These two bits set the output current limit:

Current Limit

1.2 A

1 A

600 mA

250 mA

D5 thru D18-This 14-bit word (active low) programs the

REF

time to set

desired motor speed.

Bit Number Count Number

128

256

D10

512

D11

1 024

D12

2 048

D13

4 096

D14

8 192

D15

16 384

D16

32 768

D17

65 536

D18

131 072

D19-Speed-control mode switch;

LOW = internal once-around speed signal,
HIGH = external sector data.

D20 and D21-These bits program the number

of motor poles for the once-around

FCOM

counter:

D20

D21

Motor Poles

D22 and D23-Controls the multiplexer for

DATA OUT:

D22

D23

DATA OUT

TACH (once around or sector)

Thermal Shutdown

SYNC

FCOM

Reset. The RESET terminal when pulled

low clears all serial port bits, including the D0
latch, which puts the A8906CLB in the sleep
mode.

8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

Dwg. EP-036C

SECTOR
DATA

CHIP SELECT

+5 V

VRET

C D2

CD1

RESET

CLOCK

DATA IN

RES

CF2

R F1

CF1

BYPASS

0.22

BYPASS

SERIAL PORT

FLL

MUX

COMMUTATION

DELAY

BOOST

CHARGE

PUMP

OSC (REF)

DATA OUT

FAULT

TYPICAL APPLICATION

BRAKE

FAULT

VBRK

V V

FAULT D

BRAKE

ACTIVATED

Dwg. OP-004

BRK

Braking. A dynamic braking feature of the A8906CLB shorts the
three motor windings to ground. This is accomplished by turning the
three source drivers OFF and the three sink drivers ON. Activation of
the brake can be implemented through the BRAKE input. The supply
voltage for the brake circuitry is the C

RES

voltage, allowing the brake

function to remain active after power failure. Power-down braking with
delay can be implemented by using an external RC and other compo-
nents to control the brake terminal, as shown. Brake delay can be set
using the equation below. Once the brake is activated, due to the

inherent capacitive input, the three sink
drivers will remain active until the device is
reset.

BRK

= R

1 l

Centertap. The A8906CLB internally

simulates the centertap voltage of the motor.
To obtain reliable start-up performance from
motor to motor, the motor centertap should be
connected to this terminal.

External Component Selection. Appli-

cations information regarding the selection of
external component values is available from
the factory for external component selection,
frequency-locked loop speed control, and
commutation delay capacitor selection.

BRK

FAULT -

Part Number 8906