SI-7230M
Application Note
s
Determining the output current I
O
(motor coil current)
The output current, I
O
is fixed by the following elements:
R
S
: Current detection resistor
V
CC2
: Supply voltage
R
X
: Variable current resistor
To operate a motor at maximum current level, set R
X
to
infinity (open).
To compute I
O
when different values are used for R
S
and
V
CC2
, use the approximation formula below. The maximum
ripple value I
OH
of the output current waveform can be
computed as follows:
1
(0.233•V
CC2
–0.026) [A]
I
OH(max)
=
R
S
1
(0.214•V
CC2
–0.021) [A]
I
OH(min
) =
R
S
The graph of the equations above is shown below.
s
Power down mode
SI-7230M can be operated in power down mode. The circuit
is shown below. When transistor Tr is switched on, the
reference voltage drops and the output current can be de-
creased.
9
11
13
SI-7230M
T
r
R
X
s
Surge absorption capacitor
C
A
and C
B
and capacitance
The upper diagram shown on the next page is the flow of the
counter EMF produced by the motor coils when it charges
C
A
and C
B
and the lower diagram shows the direction of the
energy discharged by C
A
and C
B
. When phase A shown in
the figure is off, the counter EMF (energy built-up by the coil
inductance) produced by the motor coils passes through the
path shown by the dotted lines and charges C
A
and C
B
.
When phase A is on, the energy stored by the capacitors are
discharged in the direction shown by the dotted lines in the
lower left diagram on the next page. The capacitors are
discharged until the voltage across their pins equal the
supply voltage V
CC
. The peak voltage V
SP
across the ca-
pacitors is given by the equation:
V
SP
=
L
•I
O
+ V
CC
C
I
OH
Waveform of the output current
SI-7230M Output current I
OH
vs. Current detection resistor Rs
3
Output current I
OH
(A)
2
1
(0.233V
CC2
– 0.026)
R
S
1 (0.214V
CC2
– 0.021)
I
OH
(min) =
R
S
I
OH
(max) =
1
where, L : Motor coil inductance between pins 4 and
5 or pins 18 and 17
C : Capacitance of C
A
and C
B
I
O
: Output current
0
0
1
2
3
4
Current detection resistor Rs (Ω)
SI-7230M Output current I
OH
vs. Variable current resistor Rx
3
R
S
= 0.3Ω
An example waveform of V
SP
is shown in the middle figure
on the next page.
A V
SP
that can be obtained when high voltage is applied can
also be produced by using the counter EMF when the coil
current rises.
Notes in selecting C
A
and C
B
.
(1) V
SP
must not exceed the breakdown voltage of the
hybrid IC (70V).
(2) C
A
and C
B
are charged/discharged in the same rate as
the phase is switched. Hence, a capacitor with excel-
lent anti-ripple characteristics should be selected.
Output current I
OH
(A)
2
R
S
= 0.6Ω
1
I
OH
(max) =
1
R
S
I
OH
(min) = 1
R
S
0
0
1.131
4.9 V
CC2
– 0.026
4.843 +
R
X
1.107
51 V
CC2
– 0.021
5.165 +
R
X
1
2
3
4
Variable current resistor Rx (kΩ)
52
SI-7200M, SI-7230M, SI-7115B, SI-7300A,
SI-7330A, SI-7500A and SI-7502
Handling Precautions
(Note: The SI-7502 is applicable for item (2) only.)
For details, refer to the relevant product specifications.
(1) Tightening torque:
The torque to be applied in tightening screws when mounting the IC on a
heatsink should be below 49N•m.
(2) Solvent:
Do not use the following solvents:
Substances that
Chlorine-based solvents
: Trichloroethylene,
dissolve the package
Trichloroethane, etc.
Aromatic hydrogen compounds : Benzene, Toluene,
Xylene, etc.
Ketone and Acetone group solvents
Substances that
weaken the package
(3) Silicone grease:
The silicone grease to be used between the aluminum base plate of the hybrid
IC and the heatsink should be any of the following:
• G-746
• YG6260
• SC102
SHINETSU CHEMICAL INDUSTRIES CO., LTD.
TOSHIBA SILICONE CO., LTD.
DOW CORNING TORAY SILICONE CO., LTD.
Gasoline, Benzine and Kerosene
Please pay sufficient attention in selecting silicone grease since oil in some
grease may penetrate the product, which will result in an extremely short
product life.
Others
• Resistance against radiation
Resistance against radiation was not considered in the development of these ICs
because it is assumed that they will be used in ordinary environment.
54
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