Figure 11. Integrated current sense amplifiers
On this board, two different current sense resistors can be connected to the internal operational amplifier, by selecting the
appropriate configuration using jumpers in J60 and J57. To measure the current from Phase A, the jumpers must be on J60
pins 1-2 and on J57 pins 1-2. To measure the DC Bus current, the jumpers must be on J60 pins 2-3 and on J57 pins 2-3.
Table 19. Measurement of the DC Bus current
Header
Setting
Description
J60
1-2
Positive end of current sense from
Phase A
2-3
Positive end of current sense from DC
Bus
J57
1-2
Negative end of current sense from
Phase A
2-3
Negative end of current sense from DC
Bus
To map the operational amplifier to the AMPx pins, the following jumpers need to be placed, too: J35 pins 1-2, J44 pins 1-2,
J45 pins 1-2.
The gain of the amplifier is set using external resistors where R198 = 199 = 2.2 kiloohm, and R196 = R200 = 40 kiloohm.
With these resistor values, the gain of the amplifier is A = R196 / (R198 + 1K) = 40K/3.2K = 12.5. Please note the
denominator considers additional 1K in series, which is the resistor before the jumper that is used to select which sense
resistor is connected to the operational amplifier.
The output voltage is shifted up by 2V5_REF, a 2.5 V supply which is mid range from the full scale voltage of the ADC, 5 V,
to accommodate positive and negative current swings. The voltage shift can be eliminated by removing R196 and replacing it
with R197 instead.
Design Considerations
S12ZVM12EVB Evaluation Board User Guide, Rev. 2, 03/2016
Freescale Semiconductor, Inc.
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