I'm trying to put a PN532 breakout board, BLE "shield" daughterboard, and a PIC microcontroller all onto one board. The PN532 breakout board has an ADP121 (5V to 3.3V) regulator, the BLE breakout has a XC6204 (5V to 3.3V regulator), and I also have an AZ1117T (5V to 3.3V) regulator for a level shifter and a RS232 transceiver chip. I'm curious about what is usually done with multiple regulators with the same input and output voltage? Should I cascade them, or choose the best one and eliminate the rest?
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1\$\begingroup\$ You want to take only the relevant chips from the boards and put them on a single board or you are willing to tie together the three already existing boards? \$\endgroup\$– Vladimir CraveroCommented Aug 28, 2014 at 17:41
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\$\begingroup\$ I'm thinking of taking only the relevant chips onto one board. Currently i have the three things attached together on a breadboard. I wasn't sure if having three regulators doing the same thing is redundant. \$\endgroup\$– user2218339Commented Aug 28, 2014 at 17:43
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1\$\begingroup\$ We do electrical engineering here. A shield is something that blocks E fields. If that's not what you mean, you need to fix your question. Otherwise, it doesn't belong here. Also, we're just supposed to know whatever a PN532, and a "BLE" are!? This is not the help desk for a specific system. \$\endgroup\$– Olin LathropCommented Aug 28, 2014 at 17:47
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1\$\begingroup\$ That BLE thing is not a shield, that's a daughter board. Learn to use the right terms or go find a arduino site where it's acceptable to talk about "sketches" and "shields" with your meaning. This is not the arduino help desk. "Shield" has a long standing and specific meaning in electronics, and it is NOT acceptable to attempt to redefine it here. \$\endgroup\$– Olin LathropCommented Aug 28, 2014 at 19:15
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1\$\begingroup\$ @OlinLathrop You said, "Also, we're just supposed to know whatever a PN532, and a "BLE" are!?" I agree with the PN part number, he should have said NFC (or NFC/RFID). But I'm surprised you questioned BLE, I would think most people on this forum know it stands for Bluetooth Low Energy. I've done a couple of BLE using products from bluegiga, and I'm certainly not going to spell out BLE everytime I use it, anymore than I would spell out NFC. (Also, I no longer have a problem with the adopted term "shield", even though I was bothered by it when Arduinos first came out.) \$\endgroup\$– tcrosleyCommented Aug 28, 2014 at 23:50
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3 Answers
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Since each board was designed separately odds are that each regulator is rated only for the chips each board includes.
The first board might need some 100mA to work and have a regulator that can go up to 150mA, and so on. It's possible that none of the regulators you already have is capable of supplying enough current for all the chips you are planning to put on the same board.
First of all you need to compute the total power consumption of all the stuff you want to put on the board. You find the values on the chip's datasheets of course, use the higest value if you are not sure. The sum of all the currents needed by the various chips will of course be the max current the board will require. Add another 10 to 20% as a safety coefficient, then look the regulator's datasheets: probably none of them can supply that much current. Finally search for a "stiff enough" regulator and use it.
answered Aug 28, 2014 at 17:48
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\$\begingroup\$ Thanks for the detailed answer! Would it actually be better if I keep the individual regulators? \$\endgroup\$ Commented Aug 28, 2014 at 18:05
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\$\begingroup\$ That entirely depends on what you are powering. It will work though. \$\endgroup\$ Commented Aug 28, 2014 at 18:23
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If you are simply packaging the three existing boards into a system, without modifying the boards, I would leave the existing regulators alone, and use the boards as purchased.
On the other hand, if you intend to design a new PC board incorporating the functions of these separate boards, then I would use a single 3.3 volt regulator, making sure it can supply enough current (and is on a suitable heatsink) for the full system.
answered Aug 28, 2014 at 18:50
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As rightly pointed out by Vladimir Cravero, having only one 3.3v linear regulator is the best way to go ahead.
3 linear regulators will unnecessarily waste 3x the power of your input supply. Plus, if you need a 3.3v rail on your PCB or circuit separately (for supplying more ICs or sensors), extending a 3.3v line from one of the 3 regulators will not be a good idea.
so, how to decide the specifications of the single 3.3v regulator? Check the datasheet of all the sensors/devices you are using. Note down the peak current, Ipeak and peak power dissipation,P(peak) of the devices. Now select a linear regulator which can supply Ipeak current and P(peak) power in normal operating conditions (aka recommended operating conditions).
