Application information, Zxbm1021, Motor current limit – Diodes ZXBM1021 User Manual
Page 14
ZXBM1021
Document number: DS36322 Rev. 2 - 2
14 of 25
April 2014
© Diodes Incorporated
ZXBM1021
Application Information
(cont.)
ThRef is capable of driving 10mA, but it is not necessary to draw much current for S
MIN
. et 10 9 in the range 5kΩ-50kΩ (1mA - 100µA).
ThRef may also be used to drive a thermistor circuit, so care must be taken to keep the total current drawn from ThRef to the correct level.
Example: Required S
MIN
of 20% = 2.6V
MI
Th ef
10
9 10
2. 5
10
9 10
Solve for R9
9
2.
10
Choose R10 = 13k
and solve for R9 which gives R9 = 12k
. The current in R10+R9 string = 5/25000 = 200µA
If S
MIN
is not required, the S
MIN
pin should be pulled up externally to Th ef by 1kΩ
Motor Current Limit
The motor current limit on ZXBM1021 compares the voltage on the Sense pin against the threshold voltage on the SetTh pin. The current limit is
triggered when the voltage at the Sense pin exceeds the threshold at SetTh. The device lowers the output PWM drive duty ratio if the voltage on
the Sense pin rises above the threshold voltage on the SetTh pin.
The threshold value at SetTh pin is set using R7 and R8 between SetThRef, SetTh and GND. The Sense voltage is generated by the motor
current flowing through the sense resistor.
It is recommended to use 100mΩ for the sense resistor on the ense pin, and vary the current limit by
changing R7 and R8.
The current limit, I
LIM
, is given by
IM
ote that etTh ef has a maximum output current of 200µA, therefore 7 8 must be larger than 25kΩ.
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
R7
R8
Rsense
Rsense
Motor
coil