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TEA3718S Scheda tecnica(PDF) 11 Page - STMicroelectronics |
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TEA3718S Scheda tecnica(HTML) 11 Page - 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 H L H L H H L L 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 11/16 |
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