DocID14109 Rev 3

7/26

AN2650

Typical application schematic

25

Due to the structure of the BCD process, the slug of the device is connected internally to

PGND and must also be connected externally to PGND.

1.1

The stepper motor driver L9942 is usually designed in an environment similar to that shown

in Figure 1.

During motor operation, electrical energy is stored in the motor coils. If the motor shuts

down, this energy is fed back to the supply voltage Vs. Thus, there is a voltage increase at

Vs, which may cause an electrical overstress of the L9942. To avoid damage to the L9942,

The energy balance can be calculated from:

From this equation, it is possible to conclude:

•

The voltage Vs2 must not exceed the maximum rating of the L9942

•

If an over voltage shut down must be avoided, the voltage Vs2 must not exceed the

minimum over voltage threshold.

Note:

As a general recommendation, STMicroelectronics recommend a minimum buffer capacitor

of 47 µF. The ripple at Vs during normal motor operation should be between 5% and 10%.

1

2

--- C

2

⋅⋅

1

2

--- L

2

1

2

--- C

2

⋅⋅

≈

⋅⋅

+

V

s1

2

L

motor

C

buffer

------------------- I

motor

2

⋅

+

V

s2

2

=

V

s2

V

s1

2

L

motor

C

buff er

------------------- I

motor

2

⋅

+

=