Datasheet BA6438S Datasheet (ROHM)

BA6438S

Motor driver ICs

3-phase motor driver

BA6438S

The BA6438S is a 3-phase, full-wave, pseudo-linear motor driver suited for VCR capstan motors. The IC has a torque
ripple cancellation circuit to reduce wow and flutter, and an output transistor saturation prevention circuit that provides
superb motor control over a wide range of current. The built-in motor power switching regulator allows applications with
low power consumption

Applications

!

3-phase VCR capstan motors

Features

!

1) 3-phase, full-wave, pseudo-linear drive system.

2) Torque ripple cancellation circuit.

3) Reversal brake based on the detection of motor
direction.

4) Output transistor (high-and low-sides) saturation
prevention circuit

5) Motor power switching regulator with oscillation circuit.

6) Output-to-GND short-circuit detection.

7) Available in SDIP 24-pin power package (with radiation
fins).

Absolute maximum ratings

!

Parameter Symbol Limits Unit

Applied voltage
Applied voltage
Power dissipation
Operating temperature
Storage temperature
Allowable output current

1 Reduced by 16mW for each increase in Ta of 1°C over 25°C.

∗

2 Should not exceed the ASO value.

∗

Recommended operating conditions

!

Parameter Symbol Min. Typ. Max. Unit
Operating power supply voltage
Operating power supply voltage

(Ta = 25°C)

V

CC

M

V

Pd
Topr −10 ∼ +75
Tstg −40 ∼ +150
I

Opeak

(Ta = 25°C)

V

V

7V

24 V

1

∗

2000

2

∗

1.7

CC

M

456 V
31223 V

mW

°C
°C

A

Motor driver ICs

Block diagram

!

CC

V

Hall

Hall

Hall

TORQUE

COMMAND

H1+Hall

10

9

−

H1

+

H2

8
7

−

H2

+

H3

6
5

−

H3

4

C

H

P

E

C

17
16

E

CR

RIPPLE

CANCELLATION

12

GND

V

CC

Amp.

CONTROL

SIGNAL

DIRECTION

AGC

TL CS

20 22

11

MOTOR

MOTOR

DIRECTION

DET

SETTING

P SIGNAL COMBINER

TSD

SHORT

CIRCUIT

OUTPUT

SATURATION

P

PCV

18

SIGNAL V

19

V

CC

ED / S

MOTOR DIRECTION SWITCHING

SWITCHING

REGULATOR

DET.

OSC

C

I

21

15

OUTPUT

SATURATION

OSC

M

V

24

A1

23

A2

3

A3

1

ATC

2

13
14

CC

REG
VS

MOTOR V

BA6438S

CC

Motor driver ICs

Pin descriptions

!

BA6438S

Pin No.

Pin name Function

1A3
2 ATC
3A2
4 PCH
5H3
6H3
7H2
8H2

9H1
10 H1
11

−

+

−

+

−

+

ED / S
12 GND
13 REG
14 V

S

15 OSC
16 ECR
17 EC
18 PCV
19 V

CC

20 TL
21 PCI
22 CS
23 A1
24 V

M

Motor output
Driver ground
Motor output
Hall amplifier AGC phase compensation
Hall signal input
Hall signal input
Hall signal input
Hall signal input
Hall signal input
Hall signal input
Forward when LOW; stop when MEDIUM; reverse when HIGH
Signal ground
Switching regulator output (sink output)
High-side saturation detection output
Oscillator capacitor connection
Torque control reference voltage input
Torque control signal input
Phase compensation for preventing driver high-side saturation
Signal power supply
Torque limiter
Phase compensation for preventing driver low-side saturation
Current sensing input
Motor output
Motor power supply

Electrical characteristics

!

Parameter Symbol Min. Typ. Max. Unit Conditions

Torque control input / output gain
Ripple cancel ratio

Output high level voltage
Output low level voltage
Oscillator frequency
Saturation detection output gain
Regulator current capacity

Not designed for radiation resistance.

(unless otherwise noted, Ta = 25°C, VCC = 5V, VM = 12V)

G

io

0.25 0.31 0.36 −

V

V
V
f

OSC

G

REGO

I

RCC

OH

OL

us

4.6 6.4 7.2 %

1.1 1.5 1.9 V I

0.95 1.3 1.65 V I
100 135 160 kHz C = 470pF

5.0 6.5 8.0 −−
30 −−mA

C =

2.2→2.1V,

E

=

L, L, H

Input

=

L, L, H→L, M, H

Input

O =

0.8A

O =

0.8A

V

O =

5V

Motor driver ICs

Circuit operation

!

(1) Pseudo-linear output and torque ripple cancellation
The IC generates a trapezoidal (pseudo-linear) output
current, whose waveform phase is 30 degrees ahead of
that of the Hall input voltage (Fig. 1).
.

30°

Hall input

Output current

Fig. 1

The trapezoidal waveform of output current would create
intermittence in the magnetic field generated by the 3­phase motor, and would result in an irregular rotation of
the motor. To prevent this, the output waveform is ob­tained by superimposing a triangular wave on the trape­zoidal wave (Fig. 2). This process is called torque ripple
cancellation.

BA6438S

A brake is applied to the motor as described in the
following.When the motor is running, pin 17 is given a
negative potential with respect to the reference potential. If
the pin 17 potential becomes positive, the IC detects the
rise of pin 17 potential above the reference potential and
activates the motor direction detecting circuit.
The motor direction detecting circuit sends a signal to the
motor direction setting circuit to reverse the motor direc­tion. This causes a braking torque that depends on the
pin 17 potential, so that the motor quickly reduces its
speed. At the same time, the positive pin 17 potential is
shifted to the reference potential, so that the motor stops
smoothly.

(3) Output current sensing and torque limitation
Pin 2 is the ground pin for the output stage. To sense the
output current, a resistor (0.5Ω recommended) is con­nected between pin 2 and the ground. The output current
is sensed by applying the voltage developed across this
resistor to pin 22 as a feedback.
The output current can be limited by adjusting the voltage
applied to pin 20. The current is limited when pin 20
reaches the same potential as pin 22. The output current

MAX

(I

. ) under this condition is given by:

Fig. 2

(2) Torque control and reversal brake
The output current can be controlled by adjusting the
voltage applied to the torque control pins (pins 16 and 17).

These pins are the inputs to a differential amplifier. A ref­erence voltage between 2.3 ~ 3.0V (2.5V recommended)
is applied to pin 16.

Output current

0

Pin 16
reference voltage (2.5 V)

Offset

Dead zone (100 mV typically)

Fig. 3

Pin 17 voltage

20P(

TL−CS

ofs

I

MAX

V

.=

R

2P

)

where R2P is the value of the resistor connected between
pin 2 and the ground, V
and (TL–CS

ofs

) is the offset between the TL and CS pins.

ATC
2pin

20P

is the voltage applied to pin 20,

V

M

24pin

1pin 3pin 23pin

Fig.4 Output circuit

Motor driver ICs

BA6438S

(4) Motor direction control (pin 11)
The motor mode is :
Forward when the pin 11 voltage is less than 0.9V,

Stop when the voltage is between 1.3

~

3.0V,
Reverse when the voltage is above 3.5V.
In the stop mode, high-and low-side output transistors
are turned off, resulting in a high impedance state.

(5) Output transistor saturation prevention circuit
This circuit monitors the output voltage and maintain the
operation of the output transistors below their saturation
levels. Operating the transistors in the linear characteristic
range provides good control over a wide range of current
and good torque characteristics even during overloading.

0

1.5V
HIGH level voltage

HIGH level output voltage

800mA

Fig.5 High level output voltage vs.

output current (reference curves)

LOW level voltage

1.3V

LOW level output voltage

0

Fig.6 Low level output voltage vs. output

current (reference curves)

800mA

Output current

Output

saturation

voltage

Output saturation voltage

ATC-pin voltage

Output current

(6) Switching regulator
The BA6438S has a switching regulator output pin. The
IC outputs a PWM signal by comparing the output of the
internal oscillator with the HIGH level output voltage
monitored.

24

V

M

+

Driver

voltage monitor

Oscillator

15
OSC

HIGH level

14

V

S

13

REG

Fig. 7

As shown in Fig. 7, the switch regulator circuit reduces the
power consumed by the IC by reducing the collector-to­emitter (C-E) voltage of the driver transistors.
Nearly all the power dissipated by the IC is dissipated be­tween the collectors and emitters of the output transistors.
More power is consumed as the C-E voltage increases and
as the output current increases.
The output transistor C-E voltage is equal to the difference
between the supply voltage and the voltage applied to the
motor. Because the voltage across the motor decreases with
decreasing drive current, the C-E voltage must increase if the
supply voltage is fixed.
Therefore, to improve the efficiency of the driver and to
prevent the power rating of the IC being exceeded, the supply
voltage must be varied in response to changes in the output
current. The supply voltage is decreased at low current and
increased at high current so that no excessive voltage is
applied between the transistor collectors and emitters .

(7) Output-to-ground short-circuit detection
The motor output pins of the IC may be short-circuited to the
ground by some fault conditions. A short-circuited output can
destroy the output transistors because of excessive current,
excessive voltage, or both. Even when a short-circuit
condition does not completely destroy the device, it can still
cause extreme overheating. To prevent this, the BA6438S
contains a short-circuit detection circuit that turns off the motor
drive current if the output-to-ground potential becomes
abnormally low.

Motor driver ICs

Application example

!

Hall

Hall

Hall

0.033

V

CC

µF

Torque control

signal

H1

10

9

H1
H2

8
7

6
5

H3

4

PCH

EC

17
16

ECR

12

+

Hall amp

−

+

−

H2

+

H3

−

Ripple

cancellation

GND

VCC

Motor direction

control signal

Motor
direction
detection

AGC

TL CS P

20 22 18 21

Motor direction

P signal combiner

saturation
prevention

PCV

0.033
µF

V

Switching

Oscil-

lator

15

CC

regulator

OSC

470PF

ED / S

setting

Motor direction switching

TSD

Short-circuit

detection

Output

C

I

0.1µF

1911

Output

saturation

detector

Signal power

supply

V

M

24

A1

23

A2

3

A3

1

ATC

2

REG

13
14

BA6438S

Motor power supply

0.5Ω

VS

0.1µF

Operation notes

!

The BA6438S has two thermal shutdown circuits (TSD1
and TSD2) to protect the IC. The typical shutdown tem­peratures are 175°C for TSD1 and 215°C for TSD 2.
When the TSD1 is activated at an elevated chip tempera­ture, the output pins (pins 1, 3, and 23) are set to the open
state. TSD1 is functional against excessive power dis­sipation, output short-circuiting, and other irregularities in
the output current, but does not work against overheating
caused by high internal currents due to externally caused
IC damage or pin-to-pin short-circuiting.
When TSD2 is activated at a higher chip temperature, the
high-and low-side output transistors are turned on, and
the internal resistance between the motor power supply
pin (pin 24) and the output ground pin (pin 2) drops to less

Fig. 8

than 3Ω. The motor power supply current (I

M

en by

R

M+R2P

VM[V]

+3

[

Ω]

I

M

=

where

M

I

is the motor supply current,

M

V

is the motor supply voltage,

M

R

is the motor power supply output resistance,

2P

R

is the pin-2 resistance.
In your application, make sure to connect between the
motor power supply and pin 24 a circuit breaker that
operates at currents less than I

M

.

) is then giv-

Motor driver ICs

Electrical characteristic curves

!

0.7

0.6

0.5

0.4

0.3

0.2

ATC VOLTAGE : ATC (V)

0.1

V

CC

=

5V, V

M

=

12V, R

ATC

=

0.5Ω

+

+

+

, H

3

) = (LMH)

, H

2

(H

1

0

0 1.0 2.0 3.0 4.0 5.0

TORQUE CONTROL : E

C

Fig.9 Output current vs. torque
control voltage

(Ι)

BA6438S

160

140

120

100

+

+

, H3

80

(H1+, H2

=

60

40

ATC VOLTAGE : ATC (mV)

20

0

(V)

−800 −600 −400 −200

)

(LLH)

TORQUE CONTROL : E

(H1+, H2+, H3

=

(LMH)

0

VCC=5V

M

=12V

V
R

ATC

+

(mV)

C

=0.5Ω

)

200 400

Fig.10 Output current vs. torque

control voltage (ΙΙ)

30

25

20

15

10

ATC VOLTAGE : ATC (mV)

−120 −80 −40

VCC=5V,VM=12V,RATC=0.5Ω

+

1

(H

5

0

TORQUE CONTROL : EC

+

+

) =

(LMH)

, H

3

, H

2

E

CR

(2.5V)

Fig.11 Output current vs. torque

control voltage (ΙΙΙ)

+40 +80

(mV)

1.8

1.6

(V)

1.4

OH

1.2

1.0

0.8

0.6

0.4

0.2

OUTPUT HIGH VOLTAGE : V

00200 400 600 800 1000

OUTPUT CURRENT : I

HIGH level output voltage

(1, 3, 23pin)

(mA)

OH

Fig.12 Output high level voltage

vs. output current

VCC=5V

1M

500k

300k
200k

100k

OSCILLATION FREQUENCY(Hz)

50k

50 100 200 300 500 1000

OSC PIN CAPACITANCE(PF)

Fig.15 Capacitance of the capacitor

connected to the OSC pin vs.
oscillation frequency

1.8

1.6

(V)

LOW level output voltage

OL

1.4

(1, 3, 23pin)

1.2

1.0

0.8

0.6

0.4

0.2

OUTPUT LOW VOLTAGE : V

0

0

400 800 1200

OUTPUT CURRENT : I

Fig.13 Output low level voltage

vs. output current

5

4

3

2

OUTPUT VOLTAGE (V)

S

1

V

0

0

Ec=2.3V

0.5 2.0 2.5 3.0

1.0 1.5
V

M

-

V

OH

Fig.16 High-side saturation detection

output voltage (pin 14) vs.
output voltage

ATC(2pin)
Pin voltage
(R

OL

2V

1.5V

(V)

ATC

1.0V

= 0.5Ω)

(mA)

0.5V

70

VCC=5V, VM=12V, R

C

=OV, ECR=2.5V

E

60

50

40

30

S OFFSET (mV)

C

20

TL -

10

0

0

TORQUE LIMIT VOLTAGE : TL(V)

ATC

=0.5Ω

0.2 0.4 0.6

Fig.14 TL-CS offset vs. torque

limit voltage

6

5

4

3

2

OUTPUT VOLTAGE (V)

1

10 20 30 40 50 60

0

SINK CURRENT(13pin) (mA)

Fig.17 Switching regulator sink

current vs. output voltage

VCC=5V

Motor driver ICs

3.0

2.5

2

1.5

1

0.5

POWER DISSIPATION : Pd (W)

0

0 40 80 120 160

AMBIENT TEMPERATURE : Ta(°C)

Fig.18 Thermal derating curve

External dimensions

!

24

(Units : mm)

23.8±0.3

18.8

BA6438S

R1.8

13

12.0±0.3

1

0.51Min.

1.778 0.55±0.1

3.2±0.2 5.3±0.3

12

SDIP-M24

13.8

0.4±0.1

0°∼15°