orb:olimex_power_supply

The Octanis Rover EPS supplies 5V dedicated for the SBPC board. The A20-OLinuXino-MICRO's main supply is by default expecting 6-11V, but these get downconverted to 5V directly. For higher efficiency, the 5V can directly be supplied at the 5V_PWR pin (top left corner; by default no connector soldered).

The following modifications must be made:

  • TOP SIDE: Remove Inductor L19.

  • BOTTOM SIDE:

Power-on issue

1.7 seconds after boot start, the Olimex board draws a substantial amount more of current during a peak time of a few ms. When powered from the 5V boost IC on the Octanis Rover EPS (TPS61232 from TI), this might be enough current to take down the voltage level from 5V to below 3.8 V, which is the minimum required input voltage for the Olimex power IC, interrupting hereby the boot process. The waveform below shows the 5V output for two successive boot trials (CH1) with CH2 = lab supply input.

This problem was observed in the following cases: - 5V supplied from TPS61232 which uses a lab supply at its input with voltage smaller than 3.9 V and 2.5 A current limit. - 5V directly supplied from “bad” (=slow, low current) lab supply

The problem did NOT happen if: - TPS61232 had sufficiently charged battery at its input (> 3.8 V). Lower limit to be tested!

The screenshot below shows the statup of the TPS61232, which was first thought to be the problem, but in the end does not seem to be the root cause. TPS61232 has soft start enabled, meaning that Vout gets loaded till the input voltage level, and then slowly boosts to the desired output voltage, with limited current. As comparison, the originally present 5V supply on the Olimex is a step-down converter whose output voltage rises linearly from 0 to 5V. It also has soft start enabled, meaning here the time it needs to reach the target output voltage.

  • orb/olimex_power_supply.txt
  • Last modified: 5 years ago
  • by raffael