TEA3718DP datasheet(11/16 Pages) STMICROELECTRONICS

11 / 16 page

The circuit is intended to drive a bipolar constant cur-

rent through one motor winding. The constant current

is generated through switch mode regulation.

There is a choice of three different current levels with

the two logic inputs lN0 and lN1. The current can

also be switched off completely.

INPUT LOGIC

If any of the logic inputs is left open, the circuit will

treat it as a high level input.

FUNCTIONAL DESCRIPTION

IN0

I N1

Current Level

No Current

Low Current

Medium Current

Maximum Current

PHASE - This input determines the direction of cur-

rent flow in the winding, depending on the motor

connections. The signal is fed through a Schmidt-

trigger for noise immunity, and through a time delay

in order to guarantee that no short-circuit occurs in

the output stage during phase-shift. High level on

the PHASE input causes the motor current flow from

Out A through the winding to Out B.

lH0 and lH1 - The current level in the motor winding

is selected with these inputs. The values of the dif-

ferent current levels are determined by the refer-

ence voltage VR togetherwith the value of the sens-

ing resistor RS.

CURRENT SENSOR

This part contains a current sensing resistor (RS), a

low pass filter (RC,CC) and three comparators. Only

one comparator is active at a time. It is activated by

the input logic according to the current level chosen

with signals IN0 and IN1. The motor current flows

through the sensing resistor RS. When the current

has increased so that the voltage across RS be-

comes higher than the reference voltage on the

other comparator input, the comparator outputgoes

high, which triggers the pulse generator and its out-

put goes high during a fixed pulse time (toff), thus

switching off the power feed to the motor winding,

and causing the motor current to decrease during

toff.

SINGLE-PULSE GENERATOR

The pulse generator is a monostable triggered on

the positive going edge of the comparator output.

The monostableoutputis high during the pulsetime,

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 current to de-

crease during toff.

If a new trigger signal should occur during toff,it is

ignored.

OUTPUT STAGE

The output stage contains four Darlington transis-

tors 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 con-

stant current through the winding.

It should be noted however, that it is not permitted

to short circuit the outputs.

VSS,VS,VR

The circuit will stand any order of turn-on or turn-off

the supply voltages VSS and VS. Normal dV/dt val-

ues are then assumed.

Preferably, VR should be tracking VSS during power-

on and power-off if VS is established.

ANALOG CONTROL

The current levels can be varied continuously if VR

is varied with a circuit varying the voltage on the

comparator terminal.

POWER LOSSES VS OUTPUT CURRENT

TEA3718-TEA3718S

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