STK672-732B-E

No. A1931-11/23

2. STK672-732B-E overcurrent detection, overheat detection, and motor terminal open detection functions

Each detection function operates using a latch system and turns output off. Because a RESET signal is required to

restore output operations, once the power supply, VDD, is turned off, you must either again apply power on reset

with VDDON or apply a RESETB=High→Low→High signal.

[Motor terminal open detection]

This hybrid IC is equipped with a function for detecting open output terminals to prevent thermal destruction of the

MOSFET due to repeated avalanche operation that occurs when an output terminal connected to the motor is open.

The open condition is determined by checking the presence or absence of the flyback current that flows in the motor

inductance during the off period of the PWM cycle.

Detection is performed by using the fact that the flyback current does not flow when a motor terminal is open.

When the current level drops, the difference with the GND potential decreases, making detection difficult. The motor

current that can be detected by motor terminal open detection is 0.7A or more with the STK672-732B-E.

<Notes on the ENABLE high edge>

When ENABLE changes from low to high and the STK672-7XXB-E performs constant-current PWM operation

that flows a negative current during the 30

μs period after the high edge, open detection may activate and stop the

driver.

The motor current setting voltage Vref must be set so that PWM operation is not performed within a period of 30

μs

after the high edge.

If the motor current setup voltage is set for the rated motor current, PWM operation is not performed during this

30

μs period after the high edge, so this is not a problem.

In addition, there is no problem with operation that lowers the current setting Vref after the motor rated current is

reached as shown in the diagram on the following page.

Whether constant-current PWM operation is performed during the 30

μs period after the high edge can be judged by

substituting the motor L and R values into the formula on the following page.

Vref= (R02÷ (R01+R02)) ×5V (or 3.3V)

IOH1= (Vref÷4.9) ÷Rs

IOH1: Motor current value to be set

IOH2= (VCC÷R) × (1-e

IOH2: Current value 30μs after the ENABLE high edge

⇒ Judgment standard: IOH1>IOH2

R01, R02, 5V (or 3.3V): See the Sample Application Circuit documents.

Rs: Current detection resistance value (

Ω)

VCC: Motor supply voltage (V)

R: Motor winding resistance (

Ω)

L: Motor winding inductance (H)

⇒ There is no problem if the IOH2 obtained by substituting t = 30μs and the motor L and R values is smaller than

the current setting value IOH1.

Used to set the motor current

Used for open detection

(Negative current does not flow

when the terminal is open.)

Current detection

resistor voltage

0V (GND potential)

MOSFET gate signal

Terminal open

PWM period