The MSP430 Launchpad is a very promising piece of hardware, it’s very affordable, and its power saving features allow it to run from batteries for a long time with minimal power consumption.
Oddly, there seems to be little options to power the launchpad when it comes to making it portable. The only solution is to attach it to a USB cable. So I decided to start a hobby project that allows the launchpad to run from batteries – the Rocketfuel Boosterpack. The Rocketfuel Boosterpack should come in two variants:
- Rechargeable – works with Lithium Ion batteries;
- Non rechargeable – works with primary batteries with voltage from 3 to 5.5V;
The non-rechargeable rocketfuel is based on the TPS78233 from Texas Instruments, that I wrote about a few weeks ago. This LDO regulator runs from an ultra low quiescent current – about 450 nA – with no load.
The rechargeable variant adds an NCP301LSN30 voltage supervisor from On Semiconductor. This chip disables the LDO when the battery’s voltage drops below 3.0V to prevent over-discharge and damage to the Lithium Ion battery. Charge management is accomplished by the BQ2057C, a simple and effective Li-Ion battery charger from Texas Instruments. There are two LED indicators, one for charging and the other for when the charge is complete.
Status of the Current Design
The current prototype works as expected but has a bug that affects the idle performance of the rechargeable rocketfuel boosterpack. There is a reverse current path through the pass transistor that makes current flow back into the input side and increase battery drain when the DC supply is disconnected. Idle current is roughly 170uA, which is way beyond the acceptable for low power and idle applications.
The measured idle current of the rocketfuel contributed by the LDO and voltage supervisor is 640nA. Mounting the pass-transistor raises current to 170uA. If the current backflow is fixed, the rocketfuel should be able to drain no more than 2 uA from the battery, or even less.
Here are pictures of the prototypes using a Nokia battery as a test case:
The next design iteration is in progress and adds a FET transistor working as a synchronous diode. This should allow current to flow forward, with minimal power losses, when the power supply is connected and completely block backward current when the power supply is removed and the system is left running from batteries.
Design files for the current version should be arriving soon.