BA6832FS

Motor driver ICs Voice coil motor driver BA6832FS The BA6832FS is a voice coil motor driver used for moving the heads of hard disc and mass-storage floppy disc drives. FApplications HDD disc and mass-storage FDD FFeatures 1) Output current is controlled by the Vctl-Vref voltage. 2) Retraction control pin. FAbsolute maximum ratings (Ta = 25_C) 3) Chip enabling pin. 4) Internal thermal shutdown circuit. FRecommended operating conditions 509 Motor driver ICs FBlock diagram BA6832FS 510 Motor driver ICs FPin descriptions BA6832FS FInput / output circuits 511 Motor driver ICs FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 12V) BA6832FS 512 Motor driver ICs FCircuit operation (1) Output current control The method of output current control depends on whether the RTL pin is HIGH or LOW. (1) When the RTL pin is LOW The voltage VRS that develops across the resistor RS between pins 10 and 11 (with reference to pin 10) is controlled by the voltage between Vctl (pin 18) and Vref (pin 19) : VRS=(Vctl*Vref) 1 (Typ.) The output current IO is given by : IO=(Vctl*Vref) / Rs (Typ.) where the positive direction is from pin 13 to pin 10. Therefore, the voltage-current conversion gain for the control input is determined by the RS value. The gain band width in this case is 80kHz (typical). (2) When the RTL pin is HIGH The VRS voltage (with reference to pin 10) is controlled by the Vrtr (pin 17) voltage (with reference to the ground) : VRS=*0.1 Vrtr / Rs (3) RTR threshold The RTR pin threshold voltage is 1.2X1.3V. The pin has a hysteresis width of about 40mV. (2) Standby mode The standby mode is activated when the CE pin is LOW; the circuit current is reduced to 0.15mA (typical), and the output pins are put to the high impedance state. The operation mode is activated when the CE pin is HIGH, and the output current becomes controllable. The pin’s threshold voltage is 1.2X1.3V. (3) Internal reference voltage The internal reference voltage Vreg is given by : Vreg=(VCC*VF) / 2 where Vreg=5.65 when VCC=12V. The output pins (pins 10 and 13) operate with reference to Vreg. BA6832FS 513 Motor driver ICs FApplication example BA6832FS 514 Motor driver ICs FOperation notes (1) Thermal shutdown circuit The IC has a built-in thermal shutdown circuit. The circuit turns off all the driver outputs when the chip junction temperature rises to about 175_C (typical). There is a temperature difference of 20_C (typical) between the temperatures at which the circuit is activated and deactivated. (2) Vctl, Vref, and input pins If voltage is applied to Vctl (pin 18) and Vref (pin 19) when the VCC voltage is outside the operating voltage, the driver outputs are turned on and a current may flow through the connected motor. The voltage of each input pin should be less than VCC and more than the ground voltage. FElectrical characteristic curves BA6832FS (3) Temperature dependence of quiescent circuit current (ICC) When the IC temperature rises with Vctl=Vref a nd CE=LOW in the quiescent mode, ICC may increase due to the temperature dependence of the standby current that flows through the high- and low-side transistors. (4) Package power dissipation The IC power dissipation changes greatly with the supply voltage and the output current. Give full consideration to the power dissipation rating when setting the supply voltage and the output current. 515 Motor driver ICs FExternal dimensions (Units: mm) BA6832FS 516