How to check the LDO output?

[surianova]

LDO output

Hi

I want to check the LDO that drive the inverters that take 1 mA.

In AC analysis, to check the loop gain and phase margin,should i

put resistor at the output to sink 1 mA or straight away the LDO
output drive the inverters?


I found out the result is different for both method.

 

[vsgiri]

LDO output

Hi surianova!

Putting a resistor to sink 1mA can only give an approximate result as the load capacitance is not modelled, which is critical in finding out frequency response. It would give a better response than what you would get with inverters connected.

Giri

 

[smartdream]

Re: LDO output

Hi surianova!

Putting a resistor to sink 1mA can only give an approximate result as the load capacitance is not modelled, which is critical in finding out frequency response. It would give a better response than what you would get with inverters connected.

Giri

Yeah, I agree with Vsgiri's suggestion. because the resistor load can give you an intuitively AC response and easy to understand^

 

[pfd001]

LDO output

both the resistor and capacitor are important for AC response

 

[mirja]

Re: LDO output

How do you generally assume/estimate the value of capacitance due to the load? say if i have to supply a digital circuit..how to go ahead with load cap value for simulation purposes?

 

[surianova]

Re: LDO output

Hi surianova!

Putting a resistor to sink 1mA can only give an approximate result as the load capacitance is not modelled, which is critical in finding out frequency response. It would give a better response than what you would get with inverters connected.

Giri

I find it is better to use the digital circuit that going to drive as the resistor load bcoz for digital circuit ,the inpedance of LDO output always changes when input of the digital circuit switch from low to high and this will affect the loop gain of the LDO and also its phase margin. The loop gain of the LDO can vary a lot depend on the DC switching point of digiatl circuit.