NCV7750GEVB
7
Because the NCV7750 is designed for 5 V or 3.3 V digital
logic levels, it is also possible to replace the 5 V supply to
the NCV7750’s VDD pin with a 3.3 V supply. To do this,
remove the jumper labelled VDD UVLO shown below and
use the nearby test post to provide a 3.3 V input.
Figure 12. UVLO Jumper and VDD Test Post Locations
It should be noted that the Arduino will not be able to
output 3.3 V digital logic levels and as such, this change
from 5 V to 3.3 V should only be done if an external input
control is to be used for all inputs to the NCV7750. This
feature is therefore useful if an external SPI controller or
Limp Home controller outputs in the 3.3 V digital logic
range.
Generating Fault Conditions
The NCV7750 is capable of detecting and reporting the
following error conditions:
•
Overload/Overcurrent Detection (OCD)
•
Overtemperature Detection (OTD)
•
Open Load Detection (OLD)
•
Undervoltage Lockout (UVLO)
During SPI transfer, the data sent out of the NCV7750
corresponds to the status of each channel. Similar to the
input, there are two bits for each channel in the output. The
meaning of each bit pair is explained in the table below:
Table 2.
Bit pair
Meaning
00
Normal operation
01
Overload or overtemperature
10
Open load
11
Open load and overloard or overtemperature
Overload generation
An overload fault may be generated by pressing an
“OCD” push button near the relays on the board. There are
four push buttons; one for each channel, positioned and
labelled according to which channel they correspond to.
These buttons produce an OCD fault by shorting VBAT to
GND through the output driver. As a result of the high
current, there will be a quick shutdown of the output driver
to protect it.
Open load generation
An open load can be generated by removing the jumpers
labelled “OL” near the relays. Like the push buttons for
OCD generation, these are positioned and labelled
according to which channel they correspond to.
These buttons produce an OLD fault by simply
disconnecting the relay coil from the output driver.
These jumpers and buttons are shown in Figure 13.
Figure 13. Open Load and Overcurrent Generation
