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I am currently designing a circuit where I have typically several IC. I have a LDO (SGM2019-ADJ) which steps 3.8V down to 3.3V with a max output of 250 mA. This 3.3V rail is dedicated to supplying an audio codec (ALC5616) which consumes a max of 4.3 mA @3.3V if I am not mistaken.

I also have the following devices:

  • MCU TIVA C TM4C123: max 30mA@3.3V
  • GPS module (L70-R): max 100mA@3.3V
  • EEPROM (M24M02-DRMN6TP): max 5mA@3.3V
  • TF card: max 45mA@3.3V
  • RS232: 1mA@3.3V

Can I safely connect all those device on the output of the LDO or should I add a second rail of 3.3V with another LDO in parallel ?

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  • \$\begingroup\$ I have a bit trouble relating the numbers of the question title to those in the question, care to elaborate? \$\endgroup\$ – PlasmaHH Jun 1 '16 at 9:34
  • \$\begingroup\$ you are right, I have renamed it. The initial idea was to know if I would need to add a second LDO or not. \$\endgroup\$ – chris Jun 1 '16 at 9:55
  • \$\begingroup\$ I have a LDO (SGM2019-ADJ) who currently transform 3.8V into 3.3V Using the word "transform" in this context is confusing. I would suggest: "attenuate 3.8 V to 3.3 V" \$\endgroup\$ – Bimpelrekkie Jun 1 '16 at 9:56
  • \$\begingroup\$ Are you sure your RS232 transceiver uses 1 mA? Most RS232 chips use a bit more than that. \$\endgroup\$ – uint128_t Jun 1 '16 at 15:44
  • \$\begingroup\$ @unit128_t I use the MAX3232CPWR, this is what seems to be written inside the datasheet. \$\endgroup\$ – chris Jun 2 '16 at 10:01
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I can not decide it for you, but I can try to suggest what you can base your decision on:

You seem to have 3mA + 30mA + 100mA + 5mA + 45mA + 1mA = 184mA consumption.

  • That is 73% of the 250mA for which the LDO promises to have 225mV drop, so probably enough headroom for now.
  • You drop ~0.5V you say, which dissipates 92mW which is probably ok, even though a quick look at the datasheet does not tell much about SOA in that regard.
  • You have some rather noisy and in relation high speed devices together with an audio codec. Depending on your requirements there, you might need to take some extra measures to decouple them, which may or may not mean a dedicated LDO for that one.
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  • \$\begingroup\$ this is the point: having a dedicated LDO or not.... this was the initial question and topic actually... \$\endgroup\$ – chris Jun 1 '16 at 10:13
  • \$\begingroup\$ @chris: I think this answer pretty much rules out the need for it in terms of power, but in terms of decoupling, there is simply not enough information given, since it ultimately depends on "meh, thats good enough for my purposes". \$\endgroup\$ – PlasmaHH Jun 1 '16 at 10:15
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If the LDO can handle the current AND it has sufficient heatsinking so that it doesn't get too hot (as long as it's less than 75'C your are probably OK as pretty much all electronics are rated to 125'C), then yes, the LDO will handle having all those devices on the same rail. You are only limited by the maximum current rating of the LDO and it's heat dissipation

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