LV8732V

No.A1483-11/26

(4) Setting constant-current control reference current

This IC is designed to automatically exercise PWM constant-current chopping control for the motor current by setting

the output current. Based on the voltage input to the VREF pin and the resistance connected between RF and GND,

the output current that is subject to the constant-current control is set using the calculation formula below :

IOUT = (VREF/5)/RF resistance

* The above setting is the output current at 100% of each excitation mode.

The voltage input to the VREF pin can be switched to four-step settings depending on the statuses of the two inputs,

ATT1 and ATT2. This is effective for reducing power consumption when motor holding current is supplied.

Attenuation function for VREF input voltage

ATT1

ATT2

Current setting reference voltage attenuation ratio

Low

Low

100%

High

Low

80%

Low

High

50%

High

High

20%

The formula used to calculate the output current when using the function for attenuating the VREF input voltage is

given below.

IOUT = (VREF/5) × (attenuation ratio)/RF resistance

Example : At VREF of 1.5V, a reference voltage setting of 100% [(ATT1, ATT2) = (L, L)] and an RF resistance of

0.3

Ω, the output current is set as shown below.

IOUT = 1.5V/5 × 100%/0.3Ω = 1.0A

If, in this state, (ATT1, ATT2) is set to (H, H), IOUT will be as follows :

IOUT = 1.0A × 20% = 200mA

In this way, the output current is attenuated when the motor holding current is supplied so that power can

be conserved.

(5) Blanking period

If, when exercising PWM constant-current chopping control over the motor current, the mode is switched from decay

to charge, the recovery current of the parasitic diode may flow to the current sensing resistance, causing noise to be

carried on the current sensing resistance pin, and this may result in erroneous detection. To prevent this erroneous

detection, a blanking period is provided to prevent the noise occurring during mode switching from being received.

During this period, the mode is not switched from charge to decay even if noise is carried on the current sensing

resistance pin.

In the stepping motor driver mode (DM = Low or Open) of this IC, the blanking time is fixed at approximately 1

μs.

In the DC motor driver mode (DM = High), the blanking time can be switched to one of two levels using the

RST/BLK pin. (Refer to "Blanking time switching function.")