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RocketFuel boosterpack

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Last minut changes...

The original idea was to place the battery beneath the PCB. However, when stacking the RFBP with the LP, the stacking height was too high and forced the use of staching headers that were way too expensive and didn't allow to stack the RFBP with other boards.

 

So, I'm in thr process of moving all components to the bottom and placing the battery on top. I keep the area of the DIP socket clear so that we can stack boards with only 10mm spacing.

 

This will allow to keep BOM cost down, make the RFBP stackable and make it more convenient to handle.

 

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After many iterations the PCB was *finally* :mrgreen: sent for fabrication.

This is my first experiment with a PCB prototype so... fingers crossed.

The prototypes will be green although I'd like to make them red if they happen to spark the interest of the community.

 

Here's a peek of the final (yup, really) design:

 

post-28545-0-50671100-1352421887_thumb.png

 

The boosterpack takes the battery on top to minimize stacking height.

Components on the solder side were kent away from obstacles (DIP package, jumpers) to minimize stacking height to the least possible.

There is a 1x2 female header located matching with the VCC connector of the LP. This isn't really necessary, but when mounted enforces the VCC jumper to be removed, virtually eliminating the risk of power supply voltage collision.

There are shunt resistors that may break the power path to the primary battery holder and the secondary battery connections. This should guarantee that properly mounted the RFBP won't try to recharge a non-rechargeable battery.

Current monitoring should be trivial using a shunt resistor. For very low power or standby applications we can use a relatively high resistor, in the order of 1kOhm and bypass the resistor when "Running" mode is needed using a jumper. I hope this can come handy to measure current comsumption during standby.

 

For batteries that lack the JST connector (or In case I mess the pinout :mrgreen: ), there are 3 pads that allow connection to '+', '-' and 'TEMP' terminals of a battery pack.

 

Can't wait to get the first unit assembled.

 

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The PCB prototypes arrived today.

These units come green. However I plan to make them red on the final version.

 

The PCB quality came quite good in general, although there are some quircks:

  • some drills are slightly off-centre. This can be noticed specially in vias, althouth it's effect is mainly cosmetic
  • There is no soldermask on vias. I have to check the PCB design to fix this
  • silkscreen clearance to copper seems too small apparently. The silkscreen got truncated around some SMD pads, which I wasn't expecting. Need to review my landpattern library.
  • Some placement drills are plated, although I didn't expected them to. PCB was manufactured from an eagle BRD file. Maybe I can fix that using gerbers the next time.

And now for the mandatory picture... :smile:

post-28545-0-95778600-1353717236_thumb.jpg

 

Currently I soldered the BQ2057C and the TPS78233 (Thanks TI, for the samples!!).

 

The remaining components are on their way and I expect them to arrive next week.

With some luck I'll be able to make the first test on the following weekend.

 

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The PCB prototypes arrived today.

These units come green. However I plan to make them red on the final version.

 

The PCB quality came quite good in general, although there are some quircks:

  • some drills are slightly off-centre. This can be noticed specially in vias, althouth it's effect is mainly cosmetic
  • There is no soldermask on vias. I have to check the PCB design to fix this
  • silkscreen clearance to copper seems too small apparently. The silkscreen got truncated around some SMD pads, which I wasn't expecting. Need to review my landpattern library.
  • Some placement drills are plated, although I didn't expected them to. PCB was manufactured from an eagle BRD file. Maybe I can fix that using gerbers the next time.

And now for the mandatory picture... :smile:

pcb-protos-1c.JPG

 

Currently I soldered the BQ2057C and the TPS78233 (Thanks TI, for the samples!!).

 

The remaining components are on their way and I expect them to arrive next week.

With some luck I'll be able to make the first test on the following weekend.

 

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to

Looking good. keep us updated!

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Good news! :mrgreen:

Remaining parts arrived today. I have 3 boards assembled, except for the stacking headers, which I'm still waiting to arrive by normal mail.

Since the sparkfun batteries are also still on transit, I am using an old BL-5B Nokia battery, soldered and soldered wires on it for a quick test.

 

So far everything looks good. Both the battery and the pass transistor are running very cool (although I'm not sure if the charger is already in CC phase) :thumbup:

 

It's kinda late so no pictures or test results right now. On the weekend I'll grab a few photos and do some testing.

Stay tuned.

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I attached the design files for this initial version of the rocketfuel. You are free to copy, modify or use it any way, although a reference to the original work would be appreciated.

 

Prototypes mounted and first tests already done. The charger circuit has one flaw: the body diode of the P-channel MOSFET creates a current path that lets current flow from the battery into the state LEDs and even the charge controller's supply pin.

 

In practice, we see both leds dimmly lit when the USB supply is removed. This can be somehow circumvented by removind one of the LEDs - the DONE LED, leaving only the indicator of CHARGE in progress.

 

With this little fix in place, the battery drain is 170uA, well above the expected figure that I estimated, but understandable, due to the current path that isn't currently blocked on the pass transistor.

 

Here are a few pics of the current prototypes:

post-28545-0-91811300-1354486820_thumb.jpg

post-28545-0-77954500-1354486682_thumb.jpg

post-28545-0-54826400-1354486632_thumb.jpg

 

I put a post in my blog with some testing I did with only the TPS78233 and the NCP301LSN30T1G.

You can check it out here: http://wp.me/p2T8F2-11

I am impressed with the quiescent current of these devices.

 

 

 

 

 

rocketfuel.sch

rocketfuel.brd

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