NJM3770AE2-TE2 datasheet, PDF - EEWORLD Datasheet

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NJM3770AE2-TE2: DescriptionMicro Peripheral IC,; CategoryThe embedded processor and controller Microcontrollers and processors; File Size173KB，10 Pages; ManufacturerNew Japan Radio Co., Ltd..

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NJM3770A

STEPPER MOTOR DRIVER

GENERAL DESCRIPTION

NJM3770A is a stepper motor driver, which consists of a

LS-TTL compatible logic input stage, a current sensor, a

monostable multivibrator and a high power H-bridge output

stage. The NJM3770A is a high power version and pin-

compatible with the NJM3717.Two NJM3770A and a small

number of external components form a complete control

and drive unit stepper motor systems.

PACKAGE OUTLINE

NJM3770AD3

NJM3770AE2

EATURES

• Half-step and full-step operation

• Switched mode bipolar constant current drive

• Wide range of current control 5 -1800 mA

• Wide voltage range 10 - 45 V

• Thermal overload protection

• Packages DIP16 (Batwing) / PLCC28 / EMP20

NJM3770AFM2

BLOCK DIAGRAM

Schmitt

Trigger

Time

Delay

Phase

≥1

–

GND

≥1

Output Stage

Monostable

off

= 0.69 • R

• C

Current Sensor

NJM3770A

Figure 1. Block diagram

NJM3770A

Current level selection.

The status of I

and I

inputs determines the current level in the motor winding. Three fixed current levels can be

selected according to the table below.

Motor current

High level

Low level

Zero current

100%

20%

Medium level 60%

H L

H H

The specific values of the different current levels are determined by the reference voltage V

together with the

value of the sensing resistor R

The peak motor current can be calculated as follows:

= (V

• 0.080) / R

[A], at 100% level

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

Current sensor

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

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

, 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, t

off

, which is determined by the timing components R

and C

off

= 0.69 • R

• C

The single pulse switches off the power feed to the motor winding, causing the winding to decrease during t

off

If a new trigger signal should occur during t

off

, it is ignored.

Output stage

The output stage contains four transistors and two diodes, connected in an H-bridge. Note that the upper recircula-

tion diodes are connected to the circuit externally. 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 3 and 4.

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 V

is applied across the motor winding, the current rise follows the equation:

= (V

/ R) • (1 - e

-(R • t ) / L

)

R = Winding resistance

L = Winding inductance

t = time

(see figure 3, arrow 1)

The motor current appears across the external sensing resistor, R

, as an analog voltage. This voltage is fed

through a low-pass filter, R

, 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 appropri-

ate upper protection diode back through the source transistor (see figure 3, 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 turns on and the motor current starts to increase

again, The cycle is repeated until the current is turned off via the logic inputs.When both I

and I

are high, all four

transistors in the output H-bridge are turned off, which means that inductive current recirculates through two opposite

free-wheeling diodes (see figure 3, arrow 3). this method of turning off the current results in a faster current decay

than if only one transistor was turned off and will therefore improve speed performance in half-stepping mode.

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