terje
03-06-05, 08:50 PM
Powered up my Isopod for the first time today, with a nominal 6VDC 700mA supply, + at the center pin of the dev. board power connector, as described in the Quick Setup Instructions for the Development Kit. This time all worked like a charm. The LEDs lit up, the IsoMax V0.61 message appeared in NMITerm, and I immediately ran WORDS and the xxxLED OFF / ON tests.
5 minutes later, the LEDs had gone out.
Cycled the power, and the LEDs lit up for about a second. On later attempts they light up only for a fraction of a second.
Apparently, the input voltage to the switching regulator board is 8.2V (the unloaded power supply voltage was 9V), but only 1V comes out of the first regulator, and 0.8V from the second. I don't have an oscilloscope, so I don't know if the oscillator is running, but I guess not... The LT1940 was lukewarm to the touch after the first couple of minutes, and cool after the breakdown.
Could you please post the schematics of the SR module in the Downloads section? I was planning to use an extra switching regulator module from NMI to power my 6 servos and a 500mW 3,3V radio module from 4 cells Li-Po, and was planning to ask you about the capacitor values. You use larger electrolytes than indicated in the data sheet, but are these tantalums? And what ceramic capacitors are used? The LT1940 is rated at max 1,4A (at both outputs simultaneously?), Have you tested your module all the way to this limit?
Switching regulators make a particular case, where too liberal usage of ceramic capacitors may not always ensure success. Their HF characteristics are just too good, and they may pull the output (sometimes even the input ?) down hard and fast enough to inhibit the oscillator.
Have of course no idea what actually happened here, or whether the SR module was permanently toasted or if the Pod is pulling the supply down... The situation is still the same with the Pod disconnected from the dev. board, and power connected directly to J1 (with no periferals connected, including the RS232 to my portable PC, which by the way was running on battery and wireless network, isolated from all other units and the mains when this happened).
Terje
In the real world everything except your oscillators will tend to oscillate...
5 minutes later, the LEDs had gone out.
Cycled the power, and the LEDs lit up for about a second. On later attempts they light up only for a fraction of a second.
Apparently, the input voltage to the switching regulator board is 8.2V (the unloaded power supply voltage was 9V), but only 1V comes out of the first regulator, and 0.8V from the second. I don't have an oscilloscope, so I don't know if the oscillator is running, but I guess not... The LT1940 was lukewarm to the touch after the first couple of minutes, and cool after the breakdown.
Could you please post the schematics of the SR module in the Downloads section? I was planning to use an extra switching regulator module from NMI to power my 6 servos and a 500mW 3,3V radio module from 4 cells Li-Po, and was planning to ask you about the capacitor values. You use larger electrolytes than indicated in the data sheet, but are these tantalums? And what ceramic capacitors are used? The LT1940 is rated at max 1,4A (at both outputs simultaneously?), Have you tested your module all the way to this limit?
Switching regulators make a particular case, where too liberal usage of ceramic capacitors may not always ensure success. Their HF characteristics are just too good, and they may pull the output (sometimes even the input ?) down hard and fast enough to inhibit the oscillator.
Have of course no idea what actually happened here, or whether the SR module was permanently toasted or if the Pod is pulling the supply down... The situation is still the same with the Pod disconnected from the dev. board, and power connected directly to J1 (with no periferals connected, including the RS232 to my portable PC, which by the way was running on battery and wireless network, isolated from all other units and the mains when this happened).
Terje
In the real world everything except your oscillators will tend to oscillate...