101

SI-7600/SI-7600D

3-Phase Stepper Motor Driver ICs (Star Connection/Delta Connection)

SI-7600/SI-7600D

Ton

Toff

ITrip

1.5V

0.5V

Fast

Decay

Slow Decay

15

5

10

0

25

050

75

Ambient temperature Ta (

°C)

(W)

100

125

150

Without

heatsink

6. Method of Calculating Power Loss of Output

MOS FET

The SI-7600 uses a MOS-FET array for output. The power loss

of this MOS FET array can be calculated as summarized below.

This is an approximate value that does not reflect parameter

variations or other factors during use in the actual application.

Therefore, heat from the MOS FET array should actually be

measured.

q Parameters for calculating power loss

To calculate the power loss of the MOS FET array, the following

parameters are needed:

(1) Control current Io (max)

(2) Excitation method

For (4) and (5), use the maximum values of the MOS FET speci-

fications.

(3) should be confirmed on the actual application.

q Power loss of Pch MOS FETs

The power loss of Pch MOS FETs is caused by the ON resis-

tance and by the chopping-OFF regenerative current flowing

through the body diodes in Fast Decay mode.

(In Slow Decay mode, the chopping-OFF regenerative current

does not flow the body diodes.)

The losses are

With these parameters, the loss Pp per MOS FET is calculated

depending on the actual excitation method as follows:

T)

×(1/12)

q Power loss of Nch MOS FETs

The power loss of Nch MOS FETs is caused by the ON resis-

tance or by the chopping-OFF regenerative current flowing

through the body diodes.

(This loss is not related to the current control method, Slow,

Mixed, or Fast Decay.)

The losses are

depending on the actual excitation method as follows:

qDetermining power loss and heatsink when SLA5017 is

used

If the SLA5017 is used in an output section, the power losses of

a Pch MOS FET and an Nch MOS FET should be multiplied by

three and added to determine the total loss P of SLA5017.

In other words, P=3

The allowable losses of SLA5017 are

Without heatsink: 5W

Infinite heatsink: 35W

Select a heatsink by considering the calculated losses, allow-

able losses, and following ratings:

When selecting a heatsink for SLA5017, be sure to check the

product temperature when in use in an actual applicaiton.

The calculated loss is an approximate value and therefore con-

tains a degree of error.

Select a heatsink so that the surface Al fin temperature of

SLA5017 will not exceed 100

°C under the worst conditions.

Relationship between RC terminal voltage and output current