LB1920

The LB1920 is designed for paper feed and drum motor drivers in FAX and PPC units.The capacitors C1 and C2 are required for faced voltage power supply stabilization. Since this IC adopts a direct PWM drive scheme and switches large currents in the output, noise can occur easily. Thus the power supply must be adequately stabilized so that this noise does not cause the IC to operate incorrectly. C 1, C2 and C3 must be connected as close as possible to GND1.In particular, C1's characteristics are easily influenced and thus requires caution.

Features of the LB1920 are:(1)the LB1920 is an output current-improved version of the LB 1824; (2)threerphase bipolar brushless motor driver; (3)digital speed control; (4)thermal shutdown circuit; (5)startlstop pin provided; (6)lock detector output; (7)crystal oscillator and divider circuits; (8)FG and error amplifiers; (9)current limner.Normally, a crystal oscillator is used with this IC. if the speed control characteristic requirements are not stringent, a ceramic oscillator could he used. To avoid problems, consult the manufactorer of the oscillator element when,selecting the oscillator element and determining the values of the external resistors and capacitors.

The absolute maximum ratings of the LB1920 can be summarized as:(1)maximum supply voltage1:30V;(2)storage temperature range:-55 to 125;(3)operating temperature range:-20 to 75;(4)maximum supply voltage2:30V;;(5)allowable power dissipation 1:3 W;(6)output current:3.1A.This IC uses the combination of a speed discriminator circuit and a PLL circuit for speed control. The speed discriminator circuit outputs an error signal once every two FG periods using a charge pump scheme. The PLL circuit outputs a phase error signal once every FG period, also using a charge pump scheme. As compared to earlier schemes that only used a speed discriminator, the combination of a PLL circuit with a speed discriminator provides improved speed variation suppression when using a motor with large load variations. Since the following formula determines the FG servo frequency, the motor speed must be set using the number of FG pulses and the crystal oscillator frequency.