10A-130W DC-DC Buck Boost Converter Module
The VIN voltage divider is compared to a 2.5V reference. The VIN voltage divider, consisting of a 500k trimmer and 36K resistor allows a low voltage cutout in the range of 2.5V to 37V, exceeding both the minimum and maximum input voltage. There appears to be no hysteresis and this is evident in testing.
VR3 and R9 makes up the external voltage divider for the error amplifier feedback input. The LTC3780 will adjust the output to ensure the voltage on VOsense is 0.800V. VOut can be calculated by 0.8V * (1 + R2/R1). The 500k trimmer and 14k resistor gives an output voltage range of 0.8V to 29V.
The adjustable over current protection consists of a non-inverting amplifier that pulls VOsense above 0.8V in the event of an over current condition. This causes the LTC3780 to back off, dropping the output voltage.
The non-inverting amplifier has a gain of 9 to 1801. With a 7mOhm current shunt, and ignoring the forward voltage drop of the diode, a range of 70mA to 13A can be expected. In practice, the minimum current sense is about 160mA.
Fault finding
On my now faulty unit, the 5V supply rail was reading 8.95V. Worst still, I had 7V feeding the run pin when the chip manufacturer warned not to exceed 6V.
My first thought was the LM358 was causing this. Removal of the part, confirmed this, and my 5V rail returned back to a more comfortable 5V.
But still no go. Looking at the data sheet, the LTC3780 has an internal 100k pull down resistor on the run pin, plus the board has a 10k to ground, both working to disable the switcher. I proceeded to solder a 10k resistor (only needed to bring run over 1.5V) between pins 7 and 8 where the LM358 once lived.
The run pin was now at 2.5V, but no go. It was now almost certain that exceeding 6V fried the run pin. I placed a new LTC3780IUH#PBF on order.
Once the new LTC3780 arrived, using hot air, I swapped it over and with my 'run' pull-up resistor still fitted, my board sprung to life. I've since soldered a 0603 resistor between pads 7 and 8 where the LM358 once stood.
Package Included:
- 1pcx LTC3780 DC-DC Buck Boost Converter Module
