NTE1857 View Datasheet(PDF) - NTE Electronics

Part Name

Description

Manufacturer

NTE1857

Integrated Circuit Stepper Motor Driver

NTE Electronics 

Bias/Set (Pin6)

This pin can be used for three functions: a) determining the maximum output sink current; b) setting

the internal logic to a known state; and c) reducing power consumption.

a) The maximum output sink current is determined by the base drive current supplied to the lower

transistors (QL’s) of each output, which in turn, is a functional of IBS. The appropriate value of

IBS is determined by;

IBS = IOD x 0.86

where IBS is in microamps, and IOD is the motor current/coil in milliamps. The value of RB (be-

tween Pin6 and GND) is then determined by:

RB =

VM – 0.7V

IBS

b) When Pin 6 is opened (raised to VM) such that IBS is < 5.0 µA, the internal logic is set to the Phase

A condition, and the four driver outputs are put into a high impedance state. The Phase A output

(Pin11) goes active (low), and input signals at Pins 7,8,9 and 10 are ignored (low), and input

signals at Pins 7, 8, 9, and 10 are ignored during this time. Upon re–establishing IBS, the driver

outputs become active, and will be in the Phase A position (L1 = L3 = VOHD, L2 = L4=VOLD).

The circuit will then respond to the inputs at Pins 7, 8, 9, and 10.

The Set function (opening Pin6) can be used as a power–up reset while supply voltages are set-

tling. A CMOS logic gate (powered by VM) can be used to control this pin.

c) Whenever the motor is not being stepped, power dissipation in the IC and in the motor may be

lowered by reducing IBS, so as to reduce the output (motor) current. Setting IBS to 75µA will re-

duce the motor current, but will not reset the internal logic as described above.

Power Dissipation

The power dissipated by the NTE1857 must be such that the junction temperature (TJ) does not ex-

ceed 150°C. The power dissipated can be expressed as:

P=(VM x IM) + (2 x IOD) [(VM – VOHD) + VOLD]

where

VM = Supply voltage:

IM = Supply current other than IOD:

IOD = Output current to each motor coil;

VOHD = Driver output high voltage;

VOLD = Driver output low voltage.

If TJ is higher than 150°C, a heat sink could be used to reduce RΘJA. In extreme cases forced air

cooling should be considered. It is assumed that a ground plane is provided under the NTE1857 (ei-

ther or both sides of the PC board) to aid in the heat dissipation. Single nominal width traces leading

from the four ground pins should be avoided as this will increase TJ, as well as provide potentially

disruptive ground noise and IR drops when switching the motor current.

Pin Connection Diagram

VD 1

L2 2

L1 3

GND 4

GND 5

BIAS/SET 6

CLK 7

OIC 8

16 VM

15 L3

14 L4

13 GND

12 GND

11 PHASE A

10 CW/CCW

9 FULL/HALF STEP

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