Application Note 1829
9
AN1829.0
March 14, 2013
This equation assumes that the only change made to the
HIP4086DEMO1Z is modifying the values of the current sensing
resistors R23 and R24.
For example: for I
LIMIT
= ±5A,
R23||R24 = 4.878V - 2.5V x 1.022k
Ω
/ (16.2k
Ω
x 5A)
R23||R24 = 0.030
Ω
An alternative method for changing the pulse-by-pulse current
limit is to modify the threshold bias voltages on the comparators.
This option is only recommended if appropriate small value
resistors for current sensing are not readily available for lab
evaluation of the HIP4086DEMO1Z. Note that the full scale
output swing of the current diff amp will not be realized with this
method.
The threshold bias resistors for the positive current limit are R1
and R38. R39 and R11B are for the negative current limit. The
required threshold is determined by Equation 2 for the desired I
m
value. For example, the Vout
CS
value for pulse-by-pulse current
limit at 5A is:
Vout
CS
= 0.119 x 5A +2.5V = 3.095V
Equation 4 sets the positive current limit bias voltage.
For pulse-by-pulse positive current limit = 5A and R38 = 10k
Ω
,
R1 = 6.155k
Ω
.
Equation 5 sets the negative current limit bias voltage.
For pulse-by-pulse positive current limit = -5A and R39 = 10k
Ω
,
R11B = 6.155k
Ω
.
In the previous examples both the positive and negative current
limit value are equal in absolute values. It is acceptable to have
different limits for the positive and negative values.
Selecting the Correct Switching Sequence
In the discussion describing the operation of a BLDC motor, a
specific hall logic pattern was used in Figure 5. Unfortunately, not
all BLDC motors use this logic pattern. In all cases, the three hall
signals are phase shifted by 60° but the logic polarity can be
different. Also, because the 0° start position is not standardized,
two rotation cycles are illustrated so that any start position can
be identified.
The following charts define all possible combinations of hall
logic. It is necessary that the hall sensor logic that matches your
motor is selected by correctly setting the dip switch prior to
applying power to the HIP4086DEMO1Z. Known specific motor
part numbers are labeled in green boxes (see Figure 14).
.
R23||R24 = 4.878V - 2.5V x 1.022k
Ω
/ (16.2k
Ω
x Im)
(EQ. 3)
R1 = 5V x R38 / (0.119 x I
m
+2.5V) - R38
(EQ. 4)
R11B = R39 x (0.119 x I
m
+2.5V) / (2.5 - 0.119 x I
m
)
(EQ. 5)
Содержание HIP4086
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