Application information, Zxbm1021 – Diodes ZXBM1021 User Manual
Page 13
ZXBM1021
Document number: DS36322 Rev. 2 - 2
13 of 25
April 2014
© Diodes Incorporated
ZXBM1021
Application Information
(cont.)
S
MIN
Minimum Speed Setting
Minimum speed setting prevents the motor from running below a set speed regardless of whether the control applied is for a slower speed (either
DC or PWM input). The minimum motor speed is chosen based on a speed below which the motor may or fail to start.
The S
MIN
pin voltage sets a maximum voltage clamp for the SPD pin.
For a DC voltage input into SPD pin, the voltage range 3V to 1V represents 0% to 100% of full speed. In order to set a minimum speed of 20%,
S
MIN
should be set 20% into this range below 3V, i.e 2.6V.
Minimum speed is set by the voltage on the S
MIN
pin, using a potential divider from the ThRef voltage output as shown below.
The S
MIN
voltage is given by
MI
Th ef
10
9 10
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
M
o
to
r
spe
e
d
(%
)
DC speed control voltage at SPD pin (V)
SPD and SMIN Voltages vs Motor Speed
S
MIN
= 2.6V
S
MIN
= 3V
H
+
ThRef
PWMSPD
P
h
2
H
i
H
-
SPD
F
G
Ph1Lo
Ph2Lo
Ph1Hi
SetThRef
Sense
S
e
tT
h
G
N
D
HBIAS
ZXBM1021
1
2
3
4
5
6
7
8
9
10
15
14
13
12
11
20
19
18
17
16
V
+
O
P
C
L
C
K
S
M
IN
C
SPD
V
C
C
R9
12k
Ω
R10
13k
Ω