Datasheet NJM3776D2 Datasheet (JRC)

DUAL CONTROLLER FOR HIGH-CURRENT STEPPER MOTOR

■ GENERAL DESCRIPTION ■ PACKAGE OUTLINE

The NJM3776 is a switch-mode (chopper), constant-current
controller intended for controlling external transistors in a high
current stepper motor application. The NJM3776 has two channels,
one for each winding of a two-phase stepper motor. The NJM3776
is equipped with a Disable input to simplify half stepping operation.
The NJM3776 contains a clock oscillator, which is common for both
driver channels, a set of comparators and flip-flops implementing
the switching control, and two output sections each containing four
outputs, two source and two sink, intended to drive an external H­bridge. Voltage supply requirements are +5 V for logic and +10 to
+45 V for the outputs.

NJM3776D2

NJM3776

■ FEATURES

• Suitable to drive any external MOS FET or bipolar power transistor

• Cross conduction prevented by time delay

• Digital filter on chip eliminates external filtering components

• Package DIP24

■ BLOCK DIAGRAM

C

V

1

R1

–
+

V

CC

NJM3776

Phase

V

CC

+
–

Dis

1

1

SGND

Pwr GND

1

Q

R
S

Logic

1

1

T

1BL

T

1AL

T

1AU

T

1BU

V

BB1

V

BB2

RC

Figure 1. Block diagram

Phase

T

Logic

+

C

V

Dis

2

2

2

R2

SRQ

–

SGND

Pwr GND

2

2

2BU

T

2AU

T

2AL

T

2BL

■ PIN CONFIGURATION

NJM3776

PWR GND

T1BL

T1BU

T1AL
T1AU
VBB1

SGND

VR

Phase

Dis

1

1

2
3
4
5
6

NJM

7

1

3776D2

8

1

C

9

1

10

1

11

1

RC Vcc

12 13

PWR GND

24

T2BL

23
22

T2BU
T2AL

21

T2AU

20

VBB 2

19

SGND

18

VR

17

C

16

2

Phase

15

Dis

14

2

2

2

2

2

Figure 2. Pin configuration

■ PIN DESCRIPTION

DIP Symbol Description

1 PWR GND 1"Power Ground" from output channel 1. Connected to the ground path (see application examples).
2 T1BL Output, channel 1, B side lower transistor. The pin will sink current when phase is high.
3 T1BU Output, channel 1, B side upper transistor. The pin will source current when phase is low.
4 T1AL Output, channel 1, A side lower transistor. The pin will sink current when phase is low.
5 T1AU Output, channel 1, A side upper transistor. The pin will source current when phase is high.
6 VBB1 Supply voltage for driving channel 1 outputs.
7 SGND

8VR

9C

10 Phase
11 Dis

1

1

1

1

1

12 RC Clock oscillator RC pin. Connect a 12 kohm resistor to V

13 Vcc Logic voltage supply, nominally +5 V.
14 Dis

15 Phase
16 C

17 VR

18 SGND

2

2

2

2

2

19 VBB2 Supply voltage for driving channel 2 outputs.
20 T2AU Output, channel 2, A side upper transistor. The pin will source current when phase is high.
21 T2AL Output, channel 2, A side lower transistor. The pin will sink current when phase is low.
22 T2BU Output, channel 2, B side upper transistor. The pin will source current when phase is low.
23 T2BL Output, channel 2, B side lower transistor. The pin will sink current when phase is high.
24 PWR GND

Sense ground channel 1. Logic ground reference and sense ground for the current control feedback­loop.
Reference voltage, channel 1. Controls the comparator threshold voltage and hence the output
current.
Comparator input channel 1. This input senses the instantaneous voltage across the sensing resistor,
filtered by the internal digital filter or an optional external RC network.
Controls the direction of channel 1 outputs T1AL, T1AU, T1BL and T1BU.
Disable input for channel 1. When HIGH, all four output transistors are turned off, which results in a
rapidly decreasing output current to zero.

and a 4 700 pF capacitor to ground to

CC

obtain the nominal switching frequency of 23.0 kHz and a digital filter blanking time of 1.0 µs.

Disable input for channel 2. When HIGH, all four output transistors are turned off, which results in a
rapidly decreasing output current to zero.
Controls the direction of channel 2 outputs T2AL, T2AU, T2BL and T2BU.
Comparator input channel 2. This input senses the instantaneous voltage across the sensing resistor,
filtered by the internal digital filter or an optional external RC network.
Reference voltage, channel 2. Controls the comparator threshold voltage and hence the output
current.
Sense ground channel 1. Logic ground reference and sense ground for the current control feedback­loop.

"Power Ground" from output channel 2. Connected to the ground path (see application examples).

2

NJM3776

■ FUNCTIONAL DESCRIPTION

Each channel of the NJM3776 consists of the following sections:

• An output section with four output transistors, two sourcing and two sinking, intended to drive the four transistors
in an external H-bridge. Each transistor is capable of driving up to 200 mA continuous current.

• A logic section that controls the output transistors.

• An S-R flip-flop, and a comparator. The clock-oscillator is common to both channels.
Constant current control is achieved by switching the output current to the windings. This is done by sensing the

peak current through the winding via a current-sensing resistor RS, effectively connected in series with the motor
winding. As the current increases, a voltage develops across the sensing resistor, which is fed back to the com­parator. At the predetermined level, defined by the voltage at the reference input VR, the comparator resets the flip­flop, which turns off the sourcing output transistor in the circuit. Consequently the correspond-ing lower external
transistor, in the H-bridge, is turned off. The turn-off of one channel is independent of the other channel. The
current decreases until the clock oscillator triggers the flip-flops of both channels simultaneously, which turns on the
output transistors again, and the cycle is repeated.

To prevent erroneous switching due to switching transients at turn-on, the NJM3776 includes a digital filter. The
clock oscillator provides a blanking pulse which is used for digital filtering of the voltage transient across the
current sensing resistor during turn-on. Due to the high output drive capability, this transient might exceed the max.
allowed voltage on the C inputs and damage the circuit. A resistor is placed in the feedback loop in order to prevent
this transient from damaging the circuit.

The current paths during turn-on, turn-off and phase shift are shown in figure 3.

1

Motor Current

Fast Current Decay
Slow Current Decay

Vmm

1 2

2

3

Rs

3

Time

Figure 3. Output stage with current paths
during turn-on, turn-off and phase shift

NJM3776

V

CH

t

d

t

50 %

t

on

t

off

t

t

V

RC

t

b

V

C

f =

s

t

ontoff

+

1

D =

t

t

on

off

+

t

on

V

OAV OB

-

■ ABSOLUTE MAXIMUM RATINGS

Parameter Pin no.* Symbol Min Max Unit

Voltage

Logic supply 13 V
Output supply 6, 19 V
Logic inputs 10, 11, 14, 15 V
Analog inputs 8, 9, 16, 17 V

CC
BB
I
A

Current

Output current t=1mS 2, 3, 4, 5, 20, 21, 22, 23 I
Logic inputs 10, 11, 14, 15 I
Analog inputs 8, 9, 16, 17 I

O
I
A

Temperature

Junction temperature T
Storage temperature T

j
stg

■ RECOMMENDED OPERATING CONDITIONS

Parameter Symbol Min Typ Max Unit
Logic supply voltage V

Supply voltage V
Output emitter voltage V
Output current continuous (see text) I
Operating ambient temperature T

Rise and fall time logic inputs t
Oscillator timing resistor R

CC

BB

E

M

A

, t

r,

f

T

4.75 5 5.25 V
10 - 40 V

- - 1.0 V

-200 - +200 mA
0 - +85 °C

--2µs
2 12 20 kohm

07V
045V

-0.3 6 V

-0.3 V

CC

V

-500 +500 mA

-10 - mA

-10 - mA

- +150 °C

-55 +150 °C

C

V

Dis

1

R1

1

897

171415

16
C

V

Dis

2

R2

2

SGND1 Pwr GND

–

R

+

S

SRQ

+
–

18
SGND

Q

2

I

CC

12 kΩ

R

T

I

RC

4 700 pF

V

CC

*

For test purposes only

C

V

I

V

V

A

IH

V

V

R

IL

Phase

1

10 11

NJM3776

V

CC

RC

T

V

RC

V

13

CC

+
–

12

Phase

I

I

I

IIH

IL

I

I

A

R

2

Figure 4. Definition of symbols and test circuit

Logic

Logic

Pwr GND

V
V
V

1

1

T

1BL

2

T

1AL

4
5

T

1AU

T

1BU

3

V

BB1

6

V

I

BB2

BB

19

I

T

2BU

22

OU

T

I

2AU

20

OU

*

I

T

2AL

OL

21

T

I

2BL

OL

23

24

2

*

Rs

CH

C

A

V

V

V

OA

BB

OB

Figure 5. Definition of terms

NJM3776

■ ELECTRICAL CHARACTERISTICS

Electrical characteristics over recommended operating conditions, unless otherwise noted. 0°C ≤ Tj ≤ +125°C .

Parameter Symbol Conditions Min Typ Max Unit

General

Supply current I
Supply current I
Total power dissipation P

Thermal shutdown junction temperature Note 2 - 160 - °C
Turn-off delay t

Logic Input

Logic HIGH input voltage V
Logic LOW input voltage V

Logic HIGH input current I
Logic LOW input current I

Analog Inputs

Input current I
|V

| mismatch V

C1—VC2

Motor Outputs

Lower transistor saturation voltage I
Lower transistor leakage current Dis1 = Dis2 = High,T

Upper transistor saturation voltage I
Upper transistor leakage current Dis1 = Dis2 = High,T

Chopper Oscillator

Chopping frequency f
Digital filter blanking time t

Note 3. - 65 70 mA

CC

Dis1= Dis2= HIGH. - 7 10 mA

CC

D

VBB= 24 V, I

= I

= 200 mA. - 0.2 0.3 W

BB1

BB2

Notes 2, 3.

dVC/dt ≥ 50 mV/µs, - 1.1 2.0 µs

d

I

= 100 mA. Note 2.

BB

IH

IL

VI = 2.4 V - - 20 µA

IH

VI = 0.4 V -0.2 -0.1 - mA

IL

Vr= 5 V - 0.5 0.8 mA

A

TA = 25°C Note 3 - 5 - mV

Cdiff

= 200 mA - 0.2 0.4 V

M

=25°C -50 -µA

= 200 mA - 0.9 1.2 V

M

CT = 4 700 pF, RT = 12 kohm - 23.0 - kHz

s

CT = 4 700 pF. Note 3. - 1.0 - µs

b

A

=25°C -50 -µA

A

2.0 - - V

- - 0.6 V

■ THERMAL CHARACTERISTICS

Parameter Symbol Conditions Min Typ Max Unit

Thermal resistance R

R

thJ-GND
thJ-A

Notes

1. All voltages are with respect to ground. Currents are positive into, negative out of specified terminal.

2. Not covered by final test program.

3. Switching duty cycle D = 30%, fs = 23.0 kHz.

Note 2 - 28 - °C/W
Note 2 - 45 - °C/W

NJM3776

■ APPLICATIONS INFORMATION
Output current

The maximum peak output, sink/source, current is 500 mA. But due to the power handling capacity of the package
this current can only be used for a short period of time (1mS). Recommended max continuous output current is 200
mA/output transistor. This is practical when driving MOS FET power transistors, since a high peak output current
capability will rapidly charge/discharge the gate capacitance, while the continuous current usage is very small.

Current control

The regulated output current level to the motor winding is determined by the voltage at the reference input and the
value of the sensing resistor, RS. The peak current through the sensing resistor (and the motor winding) can be
expressed as:
I

= 0.1·VR / RS[A]

M,peak

With a recommended value of 0.1 ohm for the sense resistor RS, a 5 V reference voltage will produce an output
current of approximately 5 A. RS should be selected for maximum motor current. Chopping frequency, winding
inductance and supply voltage also affect the current, but to much less extent.

For accurate current regulation, the sensing resistor should be a 0.5 - 1.5 W precision resistor, i. e. less than 1%

tolerance and low temperature coefficient.

Recirculating diodes

Care must be taken to assure that the recirculating current from the motor winding has a free path at all times, when
designing the external H-bridge otherwise may the voltage reach dangerous levels at the outputs. See figure 3.
Make sure that there are recirculating diodes included in the transistors, or if not design in external diodes. Also
make sure that these diodes are sufficient for the application i.e. regarding recovery time, voltage drop etc.

Rt

12 kΩ

Ct

4700 pF

V

RC

+5 V

PHASE CH 2

DISABLE CH 2

REFERENCE VOLTAGE CH 2

CC

NJM3776

13

12

Vmm

Dis

Phase

1

10 11

V

CC

+

–

Phase

2

C

V

1

R1

1

897

–
+

+
–

171415

16
C

V

Dis

2

R2

2

SGND

SGND

Pwr GND

1

Q

R
S

SRQ

18

2

Logic

Logic

1

1

24
Pwr GND

R1

270Ω

T1BL

2

T1AL

4

T1AU

5
3

T1BU

6

V

BB1

V

19

BB2

T2BU

22

20

T2AU

21

T2AL
T2BL

23

2

1000pF

R2

390Ω

R5
390Ω

R8
1kΩ

Q1
IRF9Z34 IRF9Z34

Q3 Q4
IRFZ34

R6
270Ω

R4
390Ω

R7
390Ω

Rs

0.11Ω

R3
270Ω

R8
270Ω

Q2

+

IRFZ34

Figure 6. Typical 5A stepper motor driver application with NJM3776. One channel shown.

NJM3776

Current sense filtering

At turn-on a current transient occurs, due to the recovery of the recirculation diodes and the capacitance of the
motor winding. To prevent this transient from reseting the flip-flops through the current sensing comparators, the
clock oscillator generates a blanking pulse at turn-on. The blanking pulse disables the comparators for a short time.
Thereby preventing any voltage transient across the sensing resistor from reseting the flip-flop during the time
blanking.

Select the blanking pulse time to be longer than the duration of the switching transients by selecting a proper C
value. The time is calculated as:
tb = 210 • CT[s]
As the CT value may vary from approximately 2 200 pF to 33 000 pF, a blanking time ranging from 0.5 µs to 7 µs is
possible. Nominal value is 4 700 pF, which gives a blanking time of 1.0 µs.

As the filtering action introduces a small delay, the peak value across the sensing resistor, and hence the peak
motor current, will reach a slightly higher level than what is defined by the reference voltage. The filtering delay
also limits the minimum possible output current. As the output will be on for a short time each cycle, equal to the
digital filtering blanking time plus additional internal delays, a small amount of current will flow through the winding.
Typically this current is 1-10 % of the maximum output current set by RS.

When optimizing low current performance, the filtering may be done by adding an external low pass filter in series
with the comparator C input, see figure 6. In this case the digital blanking time should be as short as possible. The
recommended filter component values are 1 kohm and 1000 pF. The transient may be reduced by adding external
recircula-ting diodes. These diodes should be of the fast switching type. By doing this the filter delay will be mini­mized. Lowering the switching frequency also helps reduce the minimum output current.

It is recommended to add the resistor R8 in the feedback loop in order to prevent the switching transient from
damaging the C inputs. See figure 6.

To create an absolute zero current, the Dis input should be HIGH.

T

Switching frequency

The frequency of the clock oscillator is set by the timing components RT and CT at the RC-pin. Since CT sets the digital
filter blanking time, the clock oscillator frequency is adjusted by RT. The value of RT is limited to 2 - 20 kohm. The
frequency is approximately calculated as:
fs = 1 / ( 0.77 • RT • CT)
Nominal component values of 12 kohm and 4 700 pF results in a clock frequency of 23.0 kHz. A lower frequency
will result in higher current ripple, but may improve low level linearity. A higher clock frequency reduces current
ripple, but increases the switching losses in the IC and possibly the iron losses in the motor.

Phase

1

Dis

1

Phase

2

Dis

2

V

R1
140%
100%

V

R2
140%
100%

I

140%
100%

–100%
–140%

I

140%
100%

–100%
–140%

MA1

MA2

Full step mode Half step mode Modified half step mode

Phase

0

1

TxBU = 1
Tx
Tx
Tx

TxBU = x
Tx
Tx
Tx

Disable

01

BL
AU
AL

BL
AU
AL

= x
= x
= 0

= 0
= x

= 1

All four off

All four off

Figure 7. Stepping modes

Figure 8. Truth table

NJM3776

Phase inputs

A logic HIGH on a Phase input causes the TxBL pin to sink current, low voltage, and the TxAU pin to source current,
high voltage. A logic LOW causes the TxAL to sink current, low voltage, and the TxBU to source current, high
voltage. A time delay prevents cross conduction in the H-bridge when changing the Phase input.
See truth table fig. 8.

Dis (Disable) inputs

A logic HIGH on the Dis inputs will turn off all four transistors of the outputs, which results in a rapidly decreasing output
current to zero. See truth table fig 8.

VR (Reference) inputs

The Vref inputs of the NJM3776 have a voltage divider with a ratio of 1 to 10 to reduce the external reference
voltage to an adequate level. The divider consists of closely matched resistors . Nominal input reference voltage is 5
V.

Interference

Due to the switching operation of NJM3776, noise and transients are generated and coupled into adjacent circuitry.
To reduce potential interference there are a few basic rules to follow:

• Use separate ground leads for power ground (the ground connection of RS), the ground leads of NJM3776, and the
ground of external analog and digital circuitry. The grounds should be connected together close to the main filtering
capacitor at the power supply.

• Decouple the supply voltages close to the NJM3776 circuit. Use a ceramic capacitor in parallel with an electrolytic
type for both VCC and VBB. Route the power supply lines close together.

• Do not place sensitive circuits close to the driver. Avoid physical current loops, and place the driver close to both
the motor and the power supply connector. The motor leads could preferably be twisted or shielded.

Motor selection

The NJM3776 is designed for two-phase bipolar stepper motors, i.e. motors that have only one winding per phase.

The chopping principle of the NJM3776 is based on a constant frequency and a varying duty cycle. This scheme
imposes certain restrictions on motor selection. Unstable chopping can occur if the chopping duty cycle exceeds
approximately 50%. See figure 5 for definitions. To avoid this, it is necessary to select a motor with a low winding
resistance and inductance, i.e. windings with fewer turns.

It is not possible to use a motor that is rated for the same voltage as the actual supply voltage. Only rated current
needs to be considered. Typical motors to be used together with the NJM3776 in a high current application, have a
voltage rating of 0.5 to 6 V, while the supply voltage usually ranges from 12 to 40 V.

Low inductance, especially in combination with a high supply voltage, enables high stepping rates. However, to
give the same torque capability at low speed, the reduced number of turns in the winding in the low resistive, low
inductive motor must be compensated by a higher current. A compromise has to be made. Select a motor with the

lowest possible winding resistance and inductance, that still gives the required torque, and use as high supply
voltage as possible, without exceeding the maximum recommended 40 V. Check that the chopping duty cycle does
not exceed 50% at maximum current.
To achieve the best utilization of the motor driver combination it is important to find the correct operation conditions in
terms of motor voltage, winding current and stepping mode to fit the motor type and the motor winding.
To find the correct operation conditions for a certain application the following procedure can be used.

1. If low noise and low resonance’s or high resolution is required, use half step or even better modified half step,
quarter step, etc. In order to implement modified half step or modes with better resolution an external sequence

generator must be used. See the testboard manual for TB 313i testboard for more information.
If the required stepping rate is high or if low cost is more important than low noise use full step mode.

2. Set the motor supply voltage and the winding currents to their maximum values (limited by the motor or the driver).
Run the motor in the application at the lowest frequency with maximum load.

3. Decrease the current, by decreasing the Vref voltage, until the motor phases out, then raise the current with the
selected torque margin, 25 to 50% as a guideline. This sets a first approximation of the suitable current level.

4. Run the motor at the highest frequency with maximum load. Decrease the motor voltage until the motor phases
out. Increase the motor voltage with 15 to 30% as a guideline to find a first estimation of the required motor voltage.
To get an even better estimation continue to adjust the current in the low frequency range and the voltage in the high
frequency range. This is a very simplified method for finding the correct operating conditions for the motor but it will
be helpful in most cases. If the motor fails to run in the high frequency range at maximum voltage a motor with lower
winding resistance should be selected. If the problems occur in the low frequency range a larger motor or a gearbox
will have to be used.

NJM3776

Thermal shutdown

The circuit is equipped with a thermal shutdown function that turns the outputs off at a chip (junction) temperature
above 160°C. Normal operation is resumed when the temperature has decreased.

Programming

Figure 7 shows the different input and output sequences for full-step, half-step and modified half-step operations.

Full-step mode

Both windings are energized at all the time with the same current, IM1 = IM2. To make the motor take one step, the
current direction (and the magnetic field direction) in one phase is reversed. The next step is then taken when the
other phase current reverses. The current changes go through a sequence of four different states which equal four
full steps until the initial state is reached again.

Half-step mode.

In the half-step mode, the current in one winding is brought to zero before a complete current reversal is made. The
motor will then have taken two half steps equalling one full step in rotary movement. The cycle is repeated, but on

the other phase. A total of eight states are sequenced until the initial state is reached again.

Half-step mode can overcome potential resonance problems. Resonances appear as a sudden loss of torque at
one or more distinct stepping rates and must be avoided so as not to loose control of the motor´s shaft position.

One disadvantage with the half-step mode is the reduced torque in the half step positions, in which current flows
through one winding only. The torque in this position is approximately 70 % of the full step position torque.

Modified half-step mode

.The torque variations in half step mode will be elimi-nated if the current is increased about 1.4 times in the half­step position. A constant torque will further reduce resonances and mechanical noise, resulting in better perfor­mance, life expectancy and reliability of the mechanical system.

Modifying the current levels must be done by bringing the reference voltage up (or down) from its nominal value
correspondingly. This can be done by using DACs or simple resistor divider networks.

See SMD and application handbook for more information on implementing modified half step.

■ TYPICAL CHARACTERISTICS

V

CE Sat

(V)

0.6

0.4

0.2

0

0 0.20 0.40

(A)

I

M

Figure 9. Typical lower transistor
saturation voltage vs. output current

V

CE Sat

1.2

1.0

0.8

0.6

0.4

0.2

0

Figure 10. Typical upper transistor
saturation voltage vs. output current

(V)

0 0.20 0.40

I

M

(A)

The specifications on this databook are only
given for information , without any guarantee
as regards either mistakes or omissions. The
application circuits in this databook are
described only to show representative
usages of the product and not intended for
the guarantee or permission of any right
including the industrial rights.