NASR-M board bring-up, onboard PSU
I’ve just achieved a major milestone in board bringup. ADP5052 works! Initially, the SW2 channel wouldn't start, and I wasn’t able to fix it for quite a long time. There were no short circuits, and the load capacitance was adequate. I chased the cold joints for a while, but haven’t found any. The VREG pin was outputting 5.1V, so there was some hope I hadn’t fried the chip.
My good old scope revealed a sparse triangular signal at the gate of Q5A, which was a hiccup. Then I went through the datasheet again. My suspicion is that the automatic PWM/PSM mode wasn't working because channel 2 was entering PSM mode, but PSM wasn’t working right either due to the low load or an unsuitable frequency. Luckliy I reserved a DNP resistor R45 that connects SYNC/MODE pin to VREG and forces PWM operation. Removing R44 and placing R45 made ADP5052 start. If you curios what the hiccup signal looks like on the scope, I have pictures.
Tags: nasr-m