11
Curtis 1352 eXm Manual, R ev. D
The drivers can be set for Constant Current, Constant Voltage, or Direct
PWM control mode.
In Constant Current mode, the driver command of 0 to 100%
is interpreted as a current from 0 to Max Output setting (up
to 3 amps). Internal current shunts are measured and fed back
to a closed loop PI controller to provide a steady current over
changing loads and supply voltages.
In Constant Voltage mode, the driver command of 0 to 100%
is interpreted as a voltage from 0 to Max Output (up to 80
volts). The battery voltage is constantly monitored and fed
back to a closed loop PI controller to provide a steady volt-
age, compensating for battery droop and discharge. If the
command is higher than the driver can output, the PWM
will max out at 100%.
In Direct PWM mode, the driver command of 0 to 100% is
directly output on the driver.
Each driver is monitored and will detect a short in the load, a failed internal
driver FET, and/or an open in the load wiring. At near 0% and 100% PWM,
it is not possible to discern each fault and some faults will not be detected.
If the driver outputs are connected to inductive loads, the coil should
have a return line to the B+ pin of the eXm. This connection provides a path
for the internal freewheel diodes to clamp the turn-off spike. Failure to make
this connection with inductive loads can cause permanent damage to the eXm
module as well as propagate failures of other electronics in the system due
to the high voltage spike caused when an inductive load turns off without a
freewheel path.
Analog inputs
The three analog inputs can easily be configured for use with potentiometers,
pressure sensors, temperature sensors, and resistive sensors (like RTDs). Each
input is read 1000 times per second by a 12-bit ADC and filtered to provide
a clean signal. The voltage reading is returned over the PDO in hundredths
of a volt, so 30 volts at an analog input will be read back over the PDO-TX
(MISO) as 3000.
2 — INSTALLATION & WIRING: I/O Signal Specications
ANALOG INPUT SPECIFICATIONS
operating
input protected esd
signal name pin voltage
impedance* voltage range tolerance
Analog Input 1 6 0 to 30 V 20 kΩ; - 1 V to B+ ± 8 kV (air
Analog Input 2 7
10 kΩ with
discharge)
Analog Input 3 8
pull-up enabled
* Tolerance ±5%.
Analog Inputs 1 and 2 have a pull-up resistor that can be programmed to
provide a low voltage at the input. This allows the ADC to read resistive values,
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