FCM8202 Fairchild Semiconductor, FCM8202 Datasheet - Page 11

• Manufacturer Part Number: FCM8202
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FCM8202 • Rev. 1.0.1
Current Feedback and Protections
The current feedback circuit performs two major
functions: (1) for generating a current feedback signal
for the motor control (2) for the over-current protection.
The I_IN pin outputs 50µA current to provide a DC bias
on the I_IN terminal to prevent a negative voltage.
Equation 1 shows the I_FB and the I_IN. A 0.5V DC
bias on I_IN is recommended. The maximum average
current signal is 1V. By using these parameters, the
maximum I_FB signal swing is 0.5V~4.5V.
Protections and Faults
Table 2. Faults Table
V
I
_
FB
Figure 18. Sine-Wave Output at CW=0

OC_Latch
Hall Error
V
SHORT
V
V
(
HOVP
Type
V
OUT
PP
PP
OS
RT
S
OV
UV

UV
) 8

(
I
BIAS
_
I
_
IN

R
Free, Reset
BIAS
State
Free
Free
Free
Free
Free
Free
Free
Free
)
(1)
11
FCM8202
protection (OCP). The first level is 1.4V, is used for
overload current protection with the OCP timer delay. If
the I_IN is higher than 1.4V, the OC timer is triggered.
The OC_Latch is enabled once the timer is exceeds its
time-out limit. The second level is 1.5V, used for the
cycle-by-cycle current limit. The PWM signal is turned
off immediately when the I_IN is > 1.5V. The third level
is 2.5V, designed for short-circuit protection. If the I_IN
is > 2.5V for over three PWM pulses, all PWM outputs
(U, V, W, X, Y, Z pins) are turned off.
Hall = 000 or 111
Open and Short
V
I_IN > 1.4V
I_IN > 2.5V
SENSE
V
V
R
Trigger
V
PP
OUT
T
PP
Figure 19. Current Feedback Flow
< 1.0V
> 18V
< 8V
provides
< 4V
> 4.5V
three
levels
V
FREE/nST 
FREE/nST 
FREE/nST 
V
SENSE
V
R
Release
V
OUT
PP
T
PP
of
> 1.2V
< 17V
> 4.5V
> 9V
< 4.0V
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over-current