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SI-7502 View Datasheet(PDF) - Sanken Electric co.,ltd.

Part Name
Description
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SI-7502 Datasheet PDF : 4 Pages
1 2 3 4
SI-7500A
Application Note
s Determining the output current IO (motor coil current)
The main elements that determine the output current are
Current detection resistor Rs, Supply voltage Vb, and Vari-
able current resistor RX.
Fig. A
(1) Normal mode
To operate a motor at maximum current level, set RX to
infinity (open).
From Fig. A, when the maximum output current ripple is
designated as IOH, its value will be,
IOH =
VRSH
RS
....................................................... [A]
VRSH can be computed as follows:
VRSH = 0.2 Vb + 0.213 (center value) .............. [B]
From equations [A] and [B], the output current IOH can
be computed as follows:
I
IOH = RS (0.2 Vb + 0.213)
The relationship between IOH and RS is shown in Fig. B.
(2) Power down mode
When an external resistor RX is connected, VRSH changes
as shown in the Fig. B even when RS is retained. Obtain
the power down output current IOHPD from Fig. B and
equation [A].
Fig. B
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
IOH
Waveform of output current
VRSH Max. (Vb = 5.0V)
VRSH Min. (Vb = 5.0V)
Vb + 0.1
VRSH(max) = 4.69 + 1.92 + 0.2 (V)
Rx
Vb + 0.09
VRSH(min) = 5.25 + 2.06 + 0.15 (V)
Rx
(Rx : k)
1
2
3
4
External resistor Rx (k)
s Thermal design
Obtain the internal power dissipation that corresponds to the output current to be required from Fig. C, multiply this by three,
and determine the size of the heatsink from the derating curve in Fig. D. The derating curve is based on junction
temperature of 125°C. However, make some allowance so that Tc is 85°C or less and then select the proper heatsink size.
Fig. C SI-7500A Internal power dissipation per phase PD
vs. Output current IO
Fig. D SI-7500A Derating curve
6
Motor : PH566-B
Vb = 5V
Holding mode
5
(Typical
value)
4
3
VCC = 30V
24V
2
20V
1
0
0
0.2
0.4
0.6
0.8
1.0
1.2
Output current lo (A)
20
150 × 100
100 × 100
15
50 × 100
10
Without
heatsink
5
Heatsink : Aluminum
Thickness : 2 mm
0
0
20
40
60
80
Ambient temperature Ta (°C)
45
 

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