Hi,
i am using the LT3795 as a LED driver with 2 output strings. 2 of the same driver circuits on the same PCB. In my application most of the time, the driver works as intended but sometimes 1 of the 2 drivers does not send an output signal on the gate.
There is also difference in the problematic drivers, in that only some of them are detecting an intern fault that is measurable on the soft start pin.
- In the case that the soft start pin shows the detection of an intern fault, the INTVcc voltage can be measured to collapse down to under 4V. This has been measured on different drivers and seems to happen occasionally.
- One tested driver does not show a detection of an intern fault on the soft start pin, but the gate does not switch as desired but stays low while the top gate output switches normally.
For the drivers where the fault was detected internally, at some point the drivers just worked again. They had been de-energized for some time and after retesting just worked like intended. They had been de-energized and retested multiple times, where the fault was persistent, but at the latest retest the driver just worked again.
My circuit is similar to the Boost mode LED Driver, as shown below. I can not share my specific application circuit publicly.
The input signals are:
Vin: 24V, CTRL1 is shorted to Vref, CTRL2 is ca. 375mV steadily. PWM is in f=4kHz with either 100%DC but only activated 0,2s / 3s for flashing purposes, or PWM is in f=4kHz with 10%DC and no further deactivation for flashing.
The driver settings we had in 2 configurations, which both produced the faults:
Driver switching frequency: 1. config: 490kHz-700kHz with spread spectrum frequency, 2. config: 570kHz without spread spectrum frequency.
soft start capacitor: 1. config: 100nF, 2. config: 1nF.
