Load Driver

LoadDrivers are used to switch power to a load. Think of them like a relay, but using solid-state devices rather than an electromechanical device. Unlike relays, they don’t have contacts that wear out over time so you get virtually unlimited cycles. LoadDrivers also come with built in protection against overloads, and diagnostics. They provide a highly reliable means of operating a wide range of loads, such as lamps, indicators, solenoids and valves.

Topology

LoadDrivers come in two varieties: high-side and low-side. A high-side load driver switches power to the positive terminal of the load and the negative terminal is typically hard-wired to ground. A low-side driver switches power to the negative terminal and the positive terminal is hard-wired to power. Check the documentation page for your particular base board to find out which topology is used.

Protection

LoadDrivers are protected against overload. If the current draw through the load driver is too high, or the temperature gets too hot, it will shutdown and latch off. Common causes of an overload are wiring errors, short circuits in the wiring, driving a load that draws too much current for the driver or a load failure. Functions are available for checking the status of the load driver, which will report if the driver is in an overload shutdown condition. To attempt to recover from a fault, a function can be invoked to reset the load driver’s status. If the cause of the fault has been cleared, then the driver will turn back on and function as normal. But if the fault that caused the overload remains, the overload shutdown will once again trigger and the driver will turn back off.

Pulse Width Modulation

LoadDrivers support PWM. By default the duty cycle is set to 100% so that the load driver turns fully on when it is enabled. Use the set_duty function to adjust the duty cycle. A freewheeling diode is fitted to handle flyback from inductive loads.

API

enabling the output

void enable(bool val)

Sets the state of the output.
true to engerize the load. false to de-energize the load.

bool enabled()

Returns the current status of the output.
true if the output is enabled, false if it is disabled.
If the output was enabled using enable(true) but was then shut-down due to an overload, enabled() will still return true even though the load has been de-energized. To check for overload shutdown, use get_status().

PWM

void set_duty(uint16_t duty)

Sets the duty cycle of the PWM output.
Units are 0.01%. 0 for 0% and 10000 for 100%.

uint16_t get_duty()

Returns the current PWM duty cycle.
Units are 0.01%. 0 for 0% and 10000 for 100%.

status

LoadDriver::Status get_status()

Returns the current status.
LoadDriver::Status::Ok if load driver is functioning normally. LoadDriver::Status::OverloadShutdown indicates an overload was detected and the load driver has been shutdown to protect it.

bool reset_status()

Resets the status, to try to recover from a fault condition.
When the load driver status is LoadDriver::Status::OverloadShutdown calling this function will reset the status back to LoadDriver::Status::Ok. Assuming the output is still enabled (ie. enabled() == true), then the driver will attempt to energize the load.