DRM33395 Datasheet, PDF (41/44 Pages) Motorola, Inc – ANALOG ICs 33395 EVALUATION MOTOR BOARD DESIGNER REFERENCE MANUALv

Freescale Semiconductor, Inc.
Design Considerations
Bus Voltage and Current Feedback Signals
The output voltage is shifted up by 1.65 V into the middle of the converter
range, to accommodate both positive and negative current swings. A
±300-mV voltage drop across the shunt resistor corresponds to a
measured current range of ±10 amps (peak value), again with 3.3V
maximum on the output.
The SMOS EVM motor board measures and limits current according to
a reconstructed bus current value that inverts swings of phase current
signals and also shifts the output up by 1.65V with gain A=1. Its
significance is adjustable with a trimmer, R131, used for setting an
over-current comparator implemented in the SMOS driver. This
comparator disables the driver outputs when the IS- (the driver pin)
voltage rises above IS+, see Figure 5-2. This happens when the
following is true:
CAUTION:
IS- ≥ IS+
≅
V_IS+off ≈ 0.08 * Imax_DCB + 1.65 [V; A]
The value, V_IS+ > 2.45V, disables the over-current circuit protection
functionality since the value on the V_IS- pin is always smaller than
2.45 volts. Allowing a larger V_IS+ value can lead to permanent damage
of the board if a current higher than 18 amps is applied!
For resetting board faults see step 6 in chapter 1.5.
I_sense_A1
I_sense_A2
+3.3V_A
R301
39 k-1%
R302 6k8 -1%
R303 6k8 -1%
2
–
3₊
R304
39 k-1%
R305 _{1.65 Vref}
390 Ω
8
LM285M ⁵
U303 ₄
R306
100 k-1%
R307
33 k-1%
1
U301A
MC33502D
GNDA
I_sense_A
R104 R105 ^V_sense_DCB
DCB_Pos
10 k-1% 2.7 k-1%
R106
120 Ω-1%
R107
180 Ω-1%
R108 R109 V_sense_DCB_half
DCB_Neg
1.8 k-1% 1.2 k-1%
Figure 5-1 Phase Current and DC Bus Voltage Sensing
33395 Evaluation Motor Board
DRM33395 Designer Reference Manual
MOTOROLA
Design Considerations
39
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