Fairchild FSB44104A, Руководство пользователя

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AN-9111 APPLICATION NOTE
© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
Rev. 1.1
• 6/26/15
14
6. Key Parameter Design Guidance
For stable operation, there are recommended parameters for
passive components and bias conditions, considering
operating characteristics of Motion SPM
®
45 LV series.
6.1. Selection of Shunt resistor
Figure 12 shows an example circuit of the SC protection
using 1-shunt resistor. The line current on the N side DC-
link is detected and the protective operation signal is passed
through the RC filter. If the current exceeds the SC
reference level, all the gates of the N-side three-phase
MOSFETs are switched to the OFF state and the F
O
fault
signal is transmitted to MCU. Since SC protection is non-
repetitive, MOSFET operation should be immediately
halted when the F
O
fault signal is given.
V
S
C
SC
3Ø
Motor
HVIC
. Level Shift
. Gate Drive
. UVLO
LVIC
. Gate Drive
. UVLO
. SCP
R
SHUNT
V
FO
COM
R
F
C
SC
VDC
Short Circuit
Current (I
SC
)
V
CSC
V
CC
Figure 12. Short circuit current protection circuit with
one shunt resistor
The value of shunt resistor is calculated by the following
equation.

Maximum SC current trip level : I
SC(max)
=1.5 * I
C
(rated
current)

SC trip referenced voltage (depends on user selection):
V
SC
= min. 0.027 V, typ. 0.03 V, max. 0.033 V
(Tolerance 10%, depends on system)

Shunt resistance : I
SC(max)
=V
SC(max)
/R
SHUNT(min)

R
SHUNT(min)
=V
SC(max)
/I
SC(max)

If the deviation of the shunt resistor is limited below ±
1%:
R
SHUNT(typ)
=R
SHUNT(min)
/0.99,R
SHUNT(max)
=R
SHUNT(typ)

1.01

Actual SC trip current level becomes:
I
SC(typ)
=V
SC(typ)
/ R
SHUNT(min)
, I
SC(min)
= V
SC(min)
/
R
SHUNT(max)

Inverter output power:
P
OUT
=
where:
V
O,LL
= Inverter output line to line voltage
MI = Modulation Index;
I
RMS
= Maximum load current of inverter; and
PF = Power Factor

Average DC current
I
DC_AVG
= V
DC_Link
/ (P
out

Eff)
where:
Eff = Inverter efficiency

The power rating of shunt resistor is calculated by the
following equation.
P
SHUNT
= (I
2
DC_AVG

R
SHUNT

Margin)/Derating Ratio
Where;
R
SHUNT
= Shunt resistor typical value at T
C
= 25 ° C
Derating Ratio = Derating ratio of shunt resistor at
T
SHUNT
= 100 ° C
(From datasheet of shunt resistor); and
Margin = Safety margin (determined by user)
Shunt Resistor Calculation Examples
Calculation Conditions:

DUT: FSB44104A

Tolerance of shunt resistor: ±1%

SC Trip Reference Voltage(V
SC
) :

V
SC(min)
= 0.0297 V, V
SC(typ)
= 0.03 V, V
SC(max)
=
0.0303 V

V
SC
= Reference voltage of external comparator
(refer to the Fig. 3)

Maximum Load Current of Inverter (I
RMS
): 28.3 A
rms

Maximum Peak Load Current of Inverter (I
C(max)
):
60 A

Modulation Index(MI) : 0.9

DC Link Voltage(V
DC_Link
): 20 V

Power Factor(PF): 0.8

Inverter Efficiency(Eff): 0.95

Shunt Resistor Value at T
C
= 25°C (R
SHUNT
): 0.5 mΩ

Derating Ration of Shunt Resistor at T
SHUNT
=
100°C: 70%

Safety Margin: 20%