3-Phase Stepper Motor Driver ICs (Star Connection/Delta Connection)
SI-7600/SI-7600D
Relationship between RC terminal voltage and output current
Ton
ITrip
I
OUT
1.5V
V
PFD
V
RC
0.5V
Fast
Decay
Slow Decay
Toff
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
ON resistance loss N1: N1=I
M2
×R
DS(ON)
Body diode loss N2: N2=I
M
×V
SD
With these parameters, the loss P
N
per MOS FET is calculated
depending on the actual excitation method as follows:
a) 2-phase excitation (T=T
ON
+T
OFF
)
P
N
=(N1+N2×T
OFF
/T)× (1/3)
b) 2-3 phase excitation (T=T
ON
+T
OFF
)
P
N
=(N1+N2×T
OFF
/T)×(1/4)+(0.5N1+N2×T
OFF
/T)×(1/12)
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×P
P
+3×P
N
The allowable losses of SLA5017 are
Without heatsink: 5W
θ
j-a=25°C/W
Infinite heatsink: 35W
θ
j-c=3.57°C/W
Select a heatsink by considering the calculated losses, allow-
able losses, and following ratings:
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
(3) Chopping ON-OFF time at current control: T
ON
, T
OFF
, t
OFFf
(T
ON
: ON time, T
OFF
: OFF time, t
OFFf
: Fast Decay time at OFF)
(4) ON resistance of MOS FET: R
DS (ON)
(5) Forward voltage of MOS FET body diode: V
SD
For (4) and (5), use the maximum values of the MOS FET speci-
fications.
(3) should be confirmed on the actual application.
(W)
15
10
Power dissipation P
1
0
×
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
ON resistance loss P1: P1=I
M2
×R
DS (ON)
Body diode loss P2: P2=I
M
×V
SD
With these parameters, the loss Pp per MOS FET is calculated
depending on the actual excitation method as follows:
a) 2-phase excitation (T=T
ON
+T
OFF
)
P
P
= (P1×T
ON
/T+P2×t
OFFf
/T)× (1/3)
b) 2-3 phase excitation (T=T
ON
+T
OFF
)
P
P
= (P1×T
ON
/T+P2×t
OFFf
/T)×(1/4)+(0.5×P1×T
ON
/T+P2×t
OFFf
/
T)×(1/12)
10
00
×
2
m
m
Al
he
at
5
Wit
hou
t he
ats
ink
sin
k
0
0
25
50
75
100 125
Ambient temperature Ta (°C)
150
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.
SI-7600/SI-7600D
101
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