NJM37717 - New Japan Radio Co., Ltd.

NJM37717

STEPPER MOTOR DRIVER

■ GENERAL DESCRIPTION ■ PACKAGE OUTLINE

NJM37717 is a stepper motor diver, which consists of a LS-TTL

compatible logic input stage, a current sensor, a monostable

multivibrator and a high power H-bridge output stage with built-in

protection diodes.

NJM37717 is a high voltage version and pin compatible with

NJM3717. The output current is up to 1200mA. Two NJM37717

and a small number of external components from a complete

control and drive unit for stepper moter system.

■ FEATURES

• Half-step and full-step modes

• Switched mode bipolar constant current drive

• Wide range of current control 5 - 1200 mA

• Wide voltage range 10 - 60 V

• Thermal overload protection

• Packages DIP16

■ BLOCK DIAGRAM

Figure 1. Block diagram

NJM37717

■ PIN DESCRIPTION

DIP Symbol Description

1 MBMotor output B, Motor current flows from MA to MB when Phase is high.

2 T Clock oscillator. Timing pin connect a 56 kΩ resistor and a 820 pF in

parallel between T and Ground.

3,14 VMM Motor supply voltage, 10 to 56 V. VMM pins should be wired together on

PCB.

4,5 GND Ground and negative supply. Note these pins are used for heatsinking.

12,13 Make sure that all ground pins are soldered onto a suitable large copper

ground plane for efficient heat sinking.

6 VCC Logic voltage supply normally +5 V.

7 I1Logic input, it controls, together with the I0 input, the current level in the

output stage. The controllable levels are fixed to 100, 60, 20, 0%.

8 Phase Controls the direction of the motor current of MA and MB outputs. Motor

current flows from MA to MB when the phase input is high.

9 I0Logic input, it controls, together with the I1 input, the current level in the

output stage. The controlable levels are fixed to 100, 60, 20, 0%.

10 C Comparator input. This input senses the instantaneous voltage across the

sensing resistor, filtered through a RC Network.

11 VRReference voltage. Controls the threshold voltage of the comparator and

hence the output current. Input resistance: typically 6.8kΩ ± 20%.

15 MAMotor output A, Motor current flows from MA to MB when Phase is high.

16 E Common emitter. Connect the sense resistor between this pin and ground.

Figure 2. Pin configurations

■ PIN CONFIGURATIONS

NJM37717

Figure 3. Definition of terms

■ FUNCTIONAL DESCRIPTION

The NJM37717 is intended to drive a bipolar constant current through one motor winding of a 2-phase stepper

motor.

Current control is achieved through switched-mode regulation, see figure 4 and 5.

Three different current levels and zero current can be selected by the input logic.

The circuit contains the following functional blocks:

• Input logic

• Current sense

• Single-pulse generator

• Output stage

Input logic

Phase input. The phase input determines the direction of the current in the motor winding. High input forces the

current from terminal MA to MB and low input from terminal MB to MA. A Schmitt trigger provides noise immunity and

a delay circuit eliminates the risk of cross conduction in the output stage during a phase shift.

Half- and full-step operation is possible.

Current level selection. The status of I0 and I1 inputs determines the current level in the motor winding. Three fixed

current levels can be selected according to the table below.

Motor current I0I1

High level 100% L L

Medium level 60% H L

Low level 20% L H

Zero current 0% H H

The specific values of the different current levels are determined by the reference voltage VR together with the value

of the sensing resistor RS.

The peak motor current can be calculated as follows:

im = (VR • 0.083) / RS [A], at 100% level

im = (VR • 0.050) / RS [A], at 60% level

im = (VR • 0.016) / RS [A], at 20% level

The motor current can also be continuously varied by modulating the voltage reference input.

NJM37717

Current sensor

The current sensor contains a reference voltage divider and three comparators for measuring each of the select-

able current levels. The motor current is sensed as a voltage drop across the current sensing resistor, RS, and

compared with one of the voltage references from the divider. When the two voltages are equal, the comparator

triggers the single-pulse generator. Only one comparator at a time is activated by the input logic.

Single-pulse generator

The pulse generator is a monostable multivibrator triggered on the positive edge of the comparator output. The

multivibrator output is high during the pulse time, toff , which is determined by the timing components RT and CT.

toff = 0.69 • RT • CT

The single pulse switches off the power feed to the motor winding, causing the winding to decrease during toff.If a

new trigger signal should occur during toff , it is ignored.

Output stage

The output stage contains four transistors and four diodes, connected in an H-bridge. The two sinking transistors

are used to switch the power supplied to the motor winding, thus driving a constant current through the winding.

See figures 4 and 5.

Overload protection

The circuit is equipped with a thermal shut-down function, which will limit the junction temperature. The output

current will be reduced if the maximum permissible junction temperature is exceeded. It should be noted, however,

that it is not short circuit protected.

Operation

When a voltage VMM is applied across the motor winding, the current rise follows the equation:

im = (VMM / R) • (1 - e-(R • t ) / L )

R = Winding resistance

L = Winding inductance

t = time

(see figure 5, arrow 1)

The motor current appears across the external sensing resistor, RS, as an analog voltage. This voltage is fed

through a low-pass filter, RCCC, to the voltage comparator input (pin 10). At the moment the sensed voltage rises

above the comparator threshold voltage, the monostable is triggered and its output turns off the conducting sink

transistor.

The polarity across the motor winding reverses and the current is forced to circulate through the appropriate

upper protection diode back through the source transistor (see figure 5, arrow 2).

After the monostable has timed out, the current has decayed and the analog voltage across the sensing resistor is

below the comparator threshold level.

The sinking transistor then closes and the motor current starts to increase again, The cycle is repeated until the

current is turned off via the logic inputs.

By reversing the logic level of the phase input (pin 8), both active transistors are turned off and the opposite pair

turned on after a slight delay. When this happens, the current must first decay to zero before it can reverse. This

current decay is steeper because the motor current is now forced to circulate back through the power supply and

the appropriate sinking transistor protection diode. This causes higher reverse voltage build-up across the winding

which results in a faster current decay (see figure 5, arrow 3).

For best speed performance of the stepper motor at half-step mode operation, the phase logic level should be

changed at the same time the current-inhibiting signal is applied (see figure 6).

NJM37717

Figure 6. Principal operating sequence

Figure 5. Output stage with current

paths for fast and slow current decay

Figure 4. Motor current (IM ),

Vertical : 200 mA/div, Horizontal: 1

ms/div, expanded part 100 µs/div

NJM37717

Figure7. Definition of symbols

■ ABSOLUTE MAXIMUM RATINGS (Ta=25°C)

Parameter Pin [DIP] Symbol Min Max Unit

Voltage

Logic supply 6 VCC 0 7 V

Motor supply 3, 14 VMM 0 60 V

Logic inputs 7, 8, 9 VI-0.3 6 V

Comparator input 10 VC-0.3 VCC V

Reference input 11 VR-0.3 15 V

Current

Motor output current 1, 15 IM-1200 +1200 mA

Logic inputs 7, 8, 9 II-10 - mA

Analog inputs 10, 11 IA-10 - mA

Temperature

Operating junction temperature Tj-40 +150 °C

Storage temperature Tstg -55 +150 °C

■ RECOMMENDED OPERATING CONDITIONS (Ta=25°C)

Parameter Symbol Min Typ Max Unit

Logic supply voltage VCC 4.75 5 5.25 V

Motor supply voltage VMM 10 - 56 V

Motor output current IM-1000 - +1000 mA

Operating junction temperature Tj-20 - +125 °C

Rise time logic inputs tr- - 2 µs

Fall time logic inputs tf- - 2 µs

NJM37717

■ ELECTRICAL CHARACTERISTICS

Electrical characteristics over recommended operating conditions, unless otherwise specified .Ta=25°C,CT = 820 pF, RT = 56kΩ

Parameter Symbol Conditions Min Typ Max Unit

General

Supply current ICC - - 25 mA

Total power dissipation PDfs = 28 kHz, IM = 500mA, VMM = 36 V - 1.4 1.7 W

Note 2, 4.

fs = 28 kHz, IM = 800mA, VMM = 36 V - 2.8 3.3 W

Note 3, 4.

Turn-off delay tddVC/dt ≥ 50 mV/µs.VMM = 60 V,RL=200Ω- 0.9 1.5 µs

Thermal shutdown junction temperature - 165 - °C

Logic Inputs

Logic HIGH input voltage VIH 2.0 - - V

Logic LOW input voltage VIL - - 0.8 V

Logic HIGH input current IIH VI = 2.4 V - - 20 µA

Logic LOW input current IIL VI = 0.4 V -0.4 - - mA

Reference Input

Input resistance RRTa = +25°C - 6.8 - kΩ

Comparator Inputs

Threshold voltage VCH VR = 5.0 V, I0 = I1 = LOW 400 415 430 mV

Threshold voltage VCM VR = 5.0 V, I0 = HIGH, I1 = LOW 240 250 265 mV

Threshold voltage VCL VR = 5.0 V, I0 = LOW, I1 = HIGH 70 80 90 mV

Input current IC-20 - - µA

Motor Outputs

Lower transistor saturation voltage IM = 500 mA - 0.9 1.2 V

IM = 800 mA - 1.1 1.4 V

Lower diode forward voltage drop IM = 500 mA - 1.2 1.5 V

IM = 800 mA - 1.3 1.7 V

Upper transistor saturation voltage IM = 500 mA - 1.0 1.25 V

IM = 800 mA - 1.2 1.5 V

Upper diode forward voltage drop IM = 500 mA - 1.0 1.25 V

IM = 800 mA - 1.2 1.45 V

Output leakage current I0 = I1 = HIGH, Ta = +25°C - - 100 µA

Monostable

Cut off time toff VMM = 10 V, ton ≥ 5 µs 27 31 35 µs

■ THERMAL CHARACTERISTICS

Parameter Symbol Conditions Min Typ Max Unit

Thermal resistance Rthj-GND DIP package. - 11 - °C/W

RthJ-A DIP package. Note 2. - 40 - °C/W

Notes

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

2. All ground pins soldered onto a 20 cm2 PCB copper area with free air convection. TA +25°C.

3. DIP package with external heatsink (Staver V7) and minimal copper area. Typical RthJ-A = 27.5°C/W. TA = +25°C.

4. Not covered by final test program.

NJM37717

■ Applications Information

Motor selection

Some stepper motors are not designed for continuous operation at maximum current. As the circuit drives a con-

stant current through the motor, its temperature can increase, both at low- and high-speed operation.

Some stepper motors have such high core losses that they are not suited for switched-mode operation.

Interference

As the circuit operates with switched-mode current regulation, interference-generation problems can arise in some

applications. A good measure is then to decouple the circuit with a 0.1 µF ceramic capacitor, located near the

package across the power line VMM and ground.

Also make sure that the VR input is sufficiently decoupled. An electrolytic capacitor should be used in the +5 V rail,

close to the circuit.

The ground leads between RS, CC and circuit GND should be kept as short as possible. This applies also to the

leads connecting RS and RC to pin 16 and pin 10 respectively.

In order to minimize electromagnetic interference, it is recommended to route MA and MB leads in parallel on the

printed circuit board directly to the terminal connector. The motor wires should be twisted in pairs, each phase

separately, when installing the motor system.

Unused inputs

Unused inputs should be connected to proper voltage levels in order to obtain the highest possible noise immunity.

Ramping

A stepper motor is a synchronous motor and does not change its speed due to load variations. This means that the

torque of the motor must be large enough to match the combined inertia of the motor and load for all operation

modes. At speed changes, the requires torque increases by the square, and the required power by the cube of the

speed change. Ramping, i.e., controlled acceleration or deceleration must then be considered to avoid motor pull-

out.

VCC , VMM

The supply voltages, VCC and VMM , can be turned on or off in any order. Normal dV/dt values are assumed.

Before a driver circuit board is removed from its system, all supply voltages must be turned off to avoid destruc-

tive transients from being generated by the motor.

Figure 8. Typical stepper motor driver application with NJM37717

NJM37717

Analog control

As the current levels can be continuously controlled by modulating the VR input, limited microstepping can be

achieved.

Switching frequency

The motor inductance, together with the pulse time, toff , determines the switching frequency of the current regulator.

The choice of motor may then require other values on the RT , CT components than those recommended in figure7,

to obtain a switching frequency above the audible range. Switching frequencies above 40 kHz are not recom-

mended because the current regulation can be affected.

Sensor resistor

The RS resistor should be of a non-inductive type, power resistor. A 1.0 ohm resistor, tolerance ≤ 1%, is a good

choice for 415 mA max motor current at VR = 5V.

The peak motor current, im , can be calculated by using the formulas:

im = (VR • 0.083) / RS [A], at 100% level

im = (VR • 0.050) / RS [A], at 60% level

im = (VR • 0.016) / RS [A], at 20% level

Heatsinking

The junction temperature of the chip highly effects the lifetime of the circuit. In high-current applications, the

heatsinking must be carefully considered.

The Rthj-a of the NJM37717 can be reduced by soldering the ground pins to a suitable copper ground plane on

the printed circuit board (see figure 10) or by applying an external heatsink type V7 or V8, see figure 9.

The diagram in figure 16 shows the maximum permissible power dissipation versus the ambient temperature in

°C, for heatsinks of the type V7, V8 or a 20 cm2 copper area respectively. Any external heatsink or printed circuit

board copper must be connected to electrical ground.

For motor currents higher than 500 mA, heatsinking is recommended to assure optimal reliability.

The diagrams in figures 9 and 10 can be used to determine the required heatsink of the circuit. In some systems,

forced-air cooling may be available to reduce the temperature rise of the circuit.

Figure 9. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK

Figure 10. Copper foil used as a heatsink

NJM37717

Figure 14. Typical upper diode voltage

drop vs. recirculating current

Figure 13. Typical lower diode voltage

drop vs. recirculating current

Figure 11. Typical source saturation vs.

output current Figure 12. Typical sink saturation vs.

output current

■ TYPICAL CHARACTERISTICS

Figure 15. Typical power dissipation vs.

motor current Figure 16. Allowable power dissipation

vs. ambient temperature

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.