AN-9111
APPLICATION NOTE
© 2015 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.1
• 6/26/15
15
Calculation Results:
I
SC(max)
: 1.5
I
C(max)
= 1.5 x 40 A = 60 A
R
SHUNT(typ)
: V
SC(typ)
/ I
SC(max)
= 0.03 V / 60 A =
0.5 mΩ
R
SHUNT(max)
: R
SHUNT(typ)
x 1.01 = 0.5 mΩ x 1.01 =
0.505 mΩ
R
SHUNT(min)
: R
SHUNT(typ)
x 0.99 = 0.5 mΩ x 0.99 =
0.495 mΩ
I
SC(min)
: V
SC(min)
/ R
SHUNT(max)
= 0.0297 V / 0.505 mΩ
= 58.8 A
I
SC(typ)
: V
SC(typ)
/ R
SHUNT(typ)
= 0.03 V / 0.5 mΩ = 60 A
V
O,LL
=
P
OUT
=
=
11.0
28.3
0.8 = 431.4 W
I
DC_AVG
= (P
OUT
/Eff) / V
DC_Link
= 22.7 A
P
SHUNT
= (I
2
DC_AVG
R
SHUNT
Margin) / Derating
Ratio = (22.7
2
0.0005
1.2) / 0.7 = 0.31 W
(Therefore, the proper power rating of shunt resistor
is over 1.0 W)
Figure 13.
Derating Curve Example of Shunt Resistor
(from RARA Elec.)
When over-current events are happened, an external circuit
is needed for over-current detection and short circuit
protection (SCP).
SPM
5V line
R
12
0.5m
3W
R
14
1.2K 1%
R
15
100K 1%
R
11
1.2K 1%
5V line
5V line
MCU
Internal port
MCU
C
15
102
C
16
104
R
17
3.3k 1%
R
18
20K
1%
R
16
10k 1%
R
19
1M
R
20
100
1%
C
17
102
Comparator
Amplifier
N
U
, N
V
, N
W
V
REF
V
SC
5V line
R
21
10k 1%
Figure 14.
Short-Circuit Protection (SCP) Circuit Using
MCU
Figure 14 is typical application circuits for SCP function
using MCU, needs external amplifier circuit and comparator
circuits. In this reference design, SC trip level (V
SC
) is 0.3 V
(I
SC(max)
=60 A) and V
REF
level is 2.5 V.
To prevent malfunction, it is recommended that an RC filter
be inserted at the C
SC
pin. To shut down MOSFETs within
3 µs when over-current situation occurs, a time constant of
1.5 ~ 2 µs is recommended
.
6.2. Fault Output Circuit
V
FO
terminal is an open-drain type; it should be pulled up
via a pull-up resistor. The resistor must satisfy the above
specifications
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
T
J
=150[
o
C]
V
FO
[
V
]
I
FO
[mA]
Figure 15.
Voltage-Current Characteristics of
V
FO
Terminal
6.3. Circuit of Input Signal (IN(xH), IN(xL))
Figure 17 shows the I/O interface circuit between the MCU
and Motion SPM
®
45 LV series. Because the Motion SPM
45 LV input logic is active high and there are built-in pull-
down resistors, external pull-down resistors are not needed.
MCU
SPM
5V-Line
IN
(UH)
, IN
(VH)
, IN
(WH)
IN
(UL)
, IN
(VL)
, IN
(WL)
V
FO
COM
R
PF
=4.7k
Ω
C
PF
=1nF
Figure 16. Recommended CPU I/O Interface Circuit
Table 9.
Maximum Ratings of Input and VF Pins
Symbol
Item
Condition
Rating
Unit
V
IN
Input
Signal
Voltage
Applied between
IN
(xH)
, IN
(xL)
-COM
-0.3 ~
V
CC
+0.3
V
V
F
Fault
Supply
Voltage
Applied between
VF-COM
-0.3 ~
V
CC
+0.3
V
The input and fault output maximum rating voltages are
shown in Table 9. Since the fault output is open-drain
configured, its rating is V
CC
+0.3 V, 15 V supply interface is
possible. However, it is recommended that the fault output
be configured with the 5 V logic supply, which is the same
Amplifier
Comparator
