LB11948T_10 Datasheet, PDF (12/13 Pages) Sanyo Semicon Device – PWM Constant Current Control 1-2 Phase Excitation Stepping Motor Driver

LB11948T
(2) Constant current settings
The reference voltages of the VREF1 and VREF2 pins can be set by dividing the resistance voltage from the 1V
regulator output pin (1VREG).
The output current is set using the VREF reference voltage applied to the VREF1 and VREF2 pins and the Re resistor
connected between the E1 and E2 pins and ground. The bias current of the output transistor also flows from the E pins
so that the Iout output current flowing to the motor is reduced by an amount equivalent to the bias current. In addition,
in controlling the constant current, the voltage is sensed by the E pins (pad area on IC chip) so that the amount
equivalent to the wire bonding resistance (rw) from the pad to the package pins is added to the current sensing
resistance (Re).
Therefore, the formula for calculating the current setting is as shown below. (Refer to Fig. 2)
IOUT = VREF / (Re + rw) - Ibias [A]
Re : Sensing resistance of resistor connected between E pins and ground
rw : Amount equivalent to wire bonding resistance from pad to pins rw = 50 - 100mΩ
Ibias : Output transistor bias current
The Ibias current corresponds to the current setting reactive current (IE) in the specifications for the electrical
characteristics.
Current setting reactive current IE ratings : Min : -22mA Typ : -17mA Max : -10.5mA
IO
Ibias
Sense current : Ie = IO+Ibias
Wire (rw)
IC E1 pin Re
VREF IC VREF1 pin
Fig. 2
(3) VREF pins
The VREF pins are the reference voltage input pins for the preset current, so take special care to ensure that they are
not affected by noise. If these pins will be affected by noise, connect a capacitor to VREF1 and VREF2 pins.
(4) Notes on the Ground Pins
Since this IC switches large currents, the following notes on ground lines must be observed.
• The PCB pattern lines in areas that handle large currents must be as wide as possible so as to have low impedances,
and must be kept as far as possible from the small signal systems.
• The ground terminals on the sensing resistors Re connected to the E pins (E1 and E2) must be connected as close as
possible to the IC GND (pin 21), PGND (pin 22), or DGND (pins 5 and 26) pins as possible.
• The capacitors between VCC and ground and between VBB and ground must be as close as possible to the
corresponding VCC and VBB pin in the pattern.
No.7947-12/13