AP1025 Datasheet, PDF (13/21 Pages) Asahi Kasei Microsystems – 45V Single Stepper Motor Driver IC

[AP1025BEN]
10.4 PWM Current Control
The current value of 100% PWM constant current setting ratio at each excitation mode of AP1025 (Iload
(100%) [A]) is determined by H-Bridge sense resistor(RIS) and PWM constant current setting voltage(VIS) as
follows.
Iload (100%)[A] = (VIS / 2.5) / RIS
--- (1)
PWM constant current setting voltage VIS
VIS damping ratio
1/2.5
H-Bridge sense resistor
RIS
Calculation example1：VIS=1V, RIS=0.5ohm
Iload (100%)[A] = (1 / 2.5) / 0.5ohm = 0.8A
--- (2)
The minimum value of the control current in the PWM constant current control in each excitation mode (Iload
(min) [A]) is determined by the following equation.
Iload(min)[A]=VM/(Rm+R_ON+RIS) × t_B × f_CP
--- (3)
Motor power supply voltage
OSC frequency
Blanking time
Motor on resistance
H-Bridge on resistance
H-Bridge sense resistor
VM
f_CP (f_CPL/ f_CPH)
t_B
R_m
R_ON
RIS
Calculation example2：VM=24V, f_CP=25kHz, t_B=2.23us, R_m=9.4ohm, R_ON=1ohm, RIS=1ohm
Iload(min)[A]=24V/(9.4ohm+1ohm+1ohm) × 2.23us × 25kHz = 0.117A
--- (4)
The current value of 100% PWM constant current setting ratio should be set so that the minimum control
current (Iload (min) [A]) becomes larger than the minimum value of the PWM constant current setting ratio in
4W1-2 phase excitation. In case of calculation example 2, the current value of the 100% PWM constant
current setting ratio (Iload (100%) [A]) is as follows.
Iload(100%)[A]=0.117/9.8%=1.19A
---(5)
If the current value of 100% PWM constant current setting value ratio (Iload (100%) [A]) is smaller than
equation (5), minimum control current value (Iload (min) [A]) may be larger than 9.8%.
015000434-E-00
- 13 -
2015/01