參數(shù)資料
型號(hào)： L6238SQA
廠商： 意法半導(dǎo)體
英文描述： 12V SENSORLESS SPINDLE MOTOR CONTROLLER
中文描述： 12V的無(wú)傳感器主軸電機(jī)控制器
文件頁(yè)數(shù)： 25/31頁(yè)
文件大小： 324K
代理商： L6238SQA
The Valley current, I
b
will thereforebe:
i
b
= 1.30 - 0.1A
i
b
= 1.20A
During the Align and Go Phase (where the power
dissipation requirements are highest, Eg is zero.
The initial time requiredto reach the Peak current
is:
Substitutingvalues:
t
init
=±
L
R
ln
1
±
I,R
V
(5.1.7)
t
init
=±
880e
±
6
4.8
ln
1
±
1.3
4.8
12
t
init
= 134.6
μ
s
The ON time can be calculatedfrom:
t
on
=
L
R
s
ln
V
R
s
±
i
b
V
R
s
±
i
t
(5.1.8)
Substitutingvalues:
t
on
=
880E
±
6
4.8
ln
12
4.8
±
1.2
12
4.8
±
1.3
t
on
= 14.67
μ
s
During the OFF time, the motor current continues
to flow through the DMOS transistorsand threfore
the voltage drop remains constant across the
windings.
The time required for the inductor currentto reach
the valleycurrent is given by:
t
off
=
Rln
I
t
I
b
(5.1.9)
Substitutingvalues:
t
off
=
880e
±
6
4.8
ln
1.3
1.2
t
off
= 14.67
μ
s
Note: thatthe parameters forthis example were selected toarrive at
a 50%duty cycle. This will notalways be the case due tofactors such
as fixed motor parameters, etc.
The Constant Off timer period can be determined
from:
t
off
=
R
slew
C
off
ln
V
chrg
V
trip
(5.1.10)
Where:
T
off
=
Constant-OFFTime
R
slew
=
SlewRate Resistor
C
off
=
Off Time Capacitor
V
chrg
=
InitialCapacitor Charge Voltage
V
trip
=
Capacitor Lower Trip Threshold
Substitutingnominal valuesgiven:
T
off
= 0.75
R
slew
C
off
Solving for C
off
C
off
=
T
off
0.75R
slew
In the example, to set the OFF timer for a 50%
duty cycle:
Given:
T
off
=
14.67
μ
s
100K
(typical Value)
R
slew
=
C
off
=
14.67e
±
6
100e
3
C
off
≈
146pF
5.1.4 Minimum ON Time
The bandwidth of the PWMloop was optimized to
reject unwanted switching noise while providing
20
μ
s/DIV
Iout A
200mA
4
D95IN324
It=1.3A
Ib=1.2A
Iavg=1.25A
Figure 5-7
L6238S
25/31
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