Please help !!! One LDO supplying voltage for two circuits

Hi all,

Can I use only one LDO that supplies current for two circuits (for example, the LDO will maintain the voltage for Amplifier and for PLL and VCO all together).

Is this concept is common or this is bad idea?

can anyone give me some links for such examples which are bad or good?

Thanks,

Re: Please help !!! One LDO supplying voltage for two circui

Well.....yeah. By LDO are you talking about a low drop out regulator? You can power up as many circuits off of one LDO that you wish. It is a trivial question. If it is a noise sensitive circuit, you need to also add R-C filtering, such as at a VCO supply pin.

Re: Please help !!! One LDO supplying voltage for two circui

Does anyone here is decent enough to answer this question?

Click to expand...

I guess that's the kind of comment that won't bring you answers quickly...

Anyway, you can use a LDO to power many circuits, but make sure that you don't bust the current capacity of the regulator.

You have to add the current consumption of the circuits that you want to power and you must make sure that its lower than what the LDO's output current. Don't forget that the LDO's maximum output current is also a function of its power dissipation, which depends greatly on the voltage difference between its input and its output.

good luck,

cyberblak

Re: Please help !!! One LDO supplying voltage for two circui

The idea behind the question is not if the LDO can supply the current, for that I can use a bigger LDO which can support the current for the several circuits.
The question is actually in the "Noise view point".
Suppose you connect LDO to VCO and an Amplifier , both fed from this LDO.
Does the noise from the VCO may affect the Voltage output of the regulator?
Is it common to connect both the VCO and an Amplifier from the same LDO?
Consider the problem from the aspect of noise....
Using LC filter in the Input of each circuit minimizes the noise? does this noise
enoght or it's much better performance improvement to connect LDO for each
component (VCO and Amplifier) by knowing that the PSRR for each LDO is big.

Thanks,

Re: Please help !!! One LDO supplying voltage for two circui

Using one common voltage regulator and a network of LC filters works sufftiently and effectively ..
This network works even better if all segments of a circuit are fed directly from the regulator, then through LC ( or Cs of different capacitancies) filter and then to that segment ..
In some papers you will find a "serial" network of LC filters, but, in my oppinion, much better results as far as noise is concerned, you will get if you connect these LC filters in "star" configuration ..
And, as additional precaution, you should consider proper shielding/screening of all sensitive segments ..
Regards,
IanP

Re: Please help !!! One LDO supplying voltage for two circui

IanP said:

Using one common voltage regulator and a network of LC filters works sufftiently and effectively ..
This network works even better if all segments of a circuit are fed directly from the regulator, then through LC ( or Cs of different capacitancies) filter and then to that segment ..
In some papers you will find a "serial" network of LC filters, but, in my oppinion, much better results as far as noise is concerned, you will get if you connect these LC filters in "star" configuration ..
And, as additional precaution, you should consider proper shielding/screening of all sensitive segments ..
Regards,
IanP

Click to expand...

Eric must be asking about on-chip stuff. No LC filter is possible.
I suggest seperate the LDO as we did.

Re: Please help !!! One LDO supplying voltage for two circui

IanP said:

Using one common voltage regulator and a network of LC filters works sufftiently and effectively ..
This network works even better if all segments of a circuit are fed directly from the regulator, then through LC ( or Cs of different capacitancies) filter and then to that segment ..
In some papers you will find a "serial" network of LC filters, but, in my oppinion, much better results as far as noise is concerned, you will get if you connect these LC filters in "star" configuration ..
And, as additional precaution, you should consider proper shielding/screening of all sensitive segments ..
Regards,
IanP

Click to expand...

Can you give me a link or a electronic scheme which demonstrate this issue or something similiar?
I am asking it because on the evaluation board of the transciver , the VCO was fed by LDO and the rest of the transceiver was fed by another LDO.
In order to lower the cost and reducing one LDO, I've asked if it's possible to use one LDO for the transceiver and for the VCO (which is inside the Trans on chip VCO).

so according to your suggestion, I use one LDO which will have LC filters before each Vcc (of the VCO and the Transc.)

but the question is, what if the VCO supply is noisy, it must affect the supply of the transceiver, does the LC filter filters the noise comming from the supply to the other supply or it just filters the noise from the LDO (by PSRR) to the Vcc of the VCO and the transceiver.

Re: Please help !!! One LDO supplying voltage for two circui

Have a look at this way of reducuing power supply noise in VCO's:
**broken link removed**
In the LC solution (your drawing), and I assume that you have some caps hooked to the output of the LDO, you have effectively two stage Π filter between VCO and transceiver: one power <-->VCO, and second: power <--> transceiver ..
And one more thing is this: linear voltage regulators are good for regulating DC voltages but they do not provide good barrier for HF noise ..
Regards,
IanP

Re: Please help !!! One LDO supplying voltage for two circui

Ericz,

You can just use original connecting way of LDO to TRX.
From proper layout routing plan, you can cut down mutual noise interferences between Vout paths of LDOs. Just use star pattern for each Vout path and put decoupling capacitor at the cross points of Vout traces to avoid noise running.
But pls put that decoupling as close to LDO output pin as possible.

regards,