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Member Since: July 6, 2011

Country: United States

  • Beginner question, just getting started with PIC micros. Bought this PIC-MT-USB and the recommended 16F877A. Would greatly appreciate if someone could provide basic step-by-step first time through instructions on how to load and run the MT-USB example code via the USB connection to Win7 PC (no RS232 port). Do I need to put a bootloader on the 16F877A first? If so, can I do that with the USB connection to the PIC-MT-USB?

  • There are some significant limitations to this circuit that should be stated somewhere in the specifications.
    First, the Power Cell - LiPo Charger/Booster does NOT enumerate with the USB host to negotiate drawing more than 100mA. Therefore, even though the MCP73831 is setup to deliver 500mA to charge the LiPoly battery, in does not do so. Some USB hosts may actually shut it down for drawing more current than 100mA without going through the proper protocol to request 500mA. If a 200mA load (for example) is connected to the battery while it is being charged, the battery will not charge when the Charger/Booster is connected to USB power.
    Second, when battery is drained down to the point where Vout turns off (Vbat < 2.6V), the charger IC (MCP73831) enters a preconditioning mode. When the Power Cell is reconnected to a 5V supply to recharge the batter, the charging current is capped at ~50mA until the battery voltage rises above 3.0V. This means that if the load circuit is still connected to the battery while it is being charged, and the load is drawing more than 50mA, the battery will not recharge.
    Third, when the battery drains down further as it remains connected to the Power Cell after Vout has turned off, the battery voltage reaches a point where the Power Cell is not able to recharge the battery at all, even with the load disconnected. However, the battery can be recharged if separately connected to a USB LiPoly Charger (PRT-10161) powered from an external 5V supply.

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