external power for EA baseboard

[lpcware]

Content originally posted in LPCWare by sravet on Sat Jan 01 21:45:03 MST 2011
I'd like to power the EA baseboard, with mbed attached, with a LiPo battery.  A single cell 3.7 volts is too low to attach to VIN, since the onboard regulator has a dropout voltage of 1.2V.  Minimum VIN is therefore 4.5V as  noted in the baseboard schematic.  The schematic also says max VIN is 5.5V.

From looking at the SP1117 datasheet I think input voltage can be much higher than 5.5V, as long as you don't exceed the limit on internal power dissipation of the regulator.  I'll need to measure the total draw from the 3.3V supply for that, too bad there isn't a current measuring jumper for that.

Am I right in thinking that a 7.4V LiPo battery pack is fine to attach to VIN, subject to being careful about regulator power dissipation?

Also, has the baseboard regulator PCB design been characterized for thermal transfer as described in the SIP1117 datasheet?

thanks,
--steve

[lpcware]

Content originally posted in LPCWare by Rob65 on Sat Jun 11 14:41:48 MST 2011

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Quote: NXP_Europe

[FONT=Consolas]We think the solution in this case is to have an external voltage regulator from the LiPo battery to 3.3V. Then connect this voltage to the "LOCAL_3V3" net. Also connect a diode from "LOCAL_3V3" (anode) to net "VIN" (cathode) in order to allow the SP1117 to be powered from the vout-end.[/FONT]

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The diode mentioned is not needed.
When using an external voltage regulator connected to the 3V3 net, the diode between the LOCAL_3V3 and 3V3 signals (D1 in the base board schematics) makes sure there is no voltage fed back into the SP1117.
But [I]do[/I] place a diode between your own regulator and the 3V3 signal to prevent that you apply power to the external regulator

If someone needs the 5V supply (to power CAN, RS485 or the RGB LED) you need to connect a regulator to the VIN signal of the board in a similar way.

As I stated also in another thread, VIN is the wrong name for the signal on the base board. This is VIN for the LPCXpresso module but it is just the 5V signal derived from one of the VBUS lines on the base board.
So it is an output signal from the base board towards the LPCXpresso module.
Reading "VIN" I would assume that this signal is primarily a power input for the base board.

On my LPCXpresso board I placed a wire between the VBUS line of the LPC-Link's VBUS signal and the VIN pin (with a diode). So now VBUS of the LPC-Link connects to VIN in a similar way as the VBUS1 and VBUS2 signals allowing me to play with the RGB LED without having to connect a second USB cable.

Rob

[lpcware]

Content originally posted in LPCWare by andersrosvall on Fri Jun 10 13:43:59 MST 2011
Hi,
The schematic shall not be interpreted as VIN can be above 5.4V.
VIN shall be +5V (+- some margin, i.e., typically 4.6-5.4V).

Kind Regards,
Anders Rosvall
Embedded Artists AB

[lpcware]

Content originally posted in LPCWare by sravet on Wed Jun 08 20:44:47 MST 2011
I know this thread is pretty old, I'm just now getting around to powering my project with an external LiPo battery.  It's a 7.4 volt battery that I thought would work fine, as far as being regulated down to 3v3.  But I just searched the schematic to see where the VIN net goes, and in addition to feeding the SP1117 regulator, it also seems to connect to VCC of the RS485 transceiver and the common anodes of the RGB LED.

This seems to be a problem, the SP491E shows VCC to be 5v, with absolute max 7v.

Is the PDF schematic correct, in that I'll probably blow up the transceiver if I connect the battery to VIN?

thanks,
--steve

[lpcware]

Content originally posted in LPCWare by sravet on Wed Jan 05 20:32:21 MST 2011
Thanks for the answer, and the explanation on the 5.5V limit.

Since I'm using mbed rather than an LPCXpresso module I think it'll work.  mbed has onboard power regulation and can take up to 14.5V.  So I think the double cell at 7.4V should work OK, as long as I keep an eye on power dissipation in the SIP1117.

thanks all,
--steve

[lpcware]

Content originally posted in LPCWare by NXP_Europe on Mon Jan 03 03:07:45 MST 2011
Hello Sravet,

[FONT=Consolas]We assume that you are talking about the LPCXpresso Base Board (Embedded Artists (EA) have many different base boards).[/FONT]
[FONT=Consolas]The 5.5V limit comes from the LPCXpresso target boards that are connected to the LPCXpresso base board. The target boards are powered via a +5V USB-type powering. This voltage goes directly into the[/FONT]
[FONT=Consolas]LPC3154 internal regulator. The limit for this is (about) 5.5V.[/FONT]
[FONT=Consolas] [/FONT]
[FONT=Consolas]The mounting of the SP1117 is not made for high power dissipation since the base board does not draw a lot of current. There is actually no specific specification on the EA design for the maximum power dissipation in the voltage regulator. In retrospect this could have been done, but on the other hand this is a prototype board and not a production board for integration into a final product.[/FONT]
[FONT=Consolas] [/FONT]
[FONT=Consolas]We think the solution in this case is to have an external voltage regulator from the LiPo battery to 3.3V. Then connect this voltage to the "LOCAL_3V3" net. Also connect a diode from "LOCAL_3V3" (anode) to net "VIN" (cathode) in order to allow the SP1117 to be powered from the vout-end.[/FONT]

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Sun Jan 02 07:57:09 MST 2011
Not familiar with it's schematic but AFAIR EA sometimes use a 6.8V Zener diode to protect voltage regulator.