Question about LDO and Bandgap Reference help me if u can

[girih192002]

Hello Guys,

I have design bandgap reference with 31 ppm/degree celsisus with 12.V reference voltage. this concept based upon weak inversion bandgap reference. and i haver desgin error amplifier with 62 dB gain and 78.5 degree phase margin.

but, i have problem that when, i connect bandgap to error amplifier comprises of resistor network , input at error amplifier from bandgap reference went to 1.4v. i am really worried. while i simuated individually each part its giving fine results


please help me if u know waht is going wrong..


thanks

 

[haff99]

Re: Question about LDO and Bandgap Reference help me if u ca

Without seeing the circuit, adding a resistor divider off of the bandgap is basically like a load to the band gap. THis added load may be causing a systematic offset in your bandgap. If you simulate the bandgap just with the resistor network does the voltage go to 1.4V? If this is the case, you can buffer the bandgap voltage with a unity gain buffer. THis would elminate the loading effects.

 

[girih192002]

Re: Question about LDO and Bandgap Reference help me if u ca

Without seeing the circuit, adding a resistor divider off of the bandgap is basically like a load to the band gap. THis added load may be causing a systematic offset in your bandgap. If you simulate the bandgap just with the resistor network does the voltage go to 1.4V? If this is the case, you can buffer the bandgap voltage with a unity gain buffer. THis would elminate the loading effects.

I have implemented weak inversion bandgap reference topology, when i i have connected resistor as load at output of bandgap reference from 100 ohm to 1k ohm . then reference voltage gets drop down from 1.26v to certain millivolt.but when i connect it with error amplifier it will g to 1.4 v .

i got ur point but i need some more clarification about it from you. is there any problem in error amplfier ...? i thought it is loading problem of BGR.
give reply ASAP...

thanks for co-operation.

Added after 11 minutes:

here is my circuit topology is based upon weak inversion bandgap reference, tell where to connect UGB here

 

[Areky_qin]

from your case, the loading math have some issues.

 

[girih192002]

Re: Question about LDO and Bandgap Reference help me if u ca

Without seeing the circuit, adding a resistor divider off of the bandgap is basically like a load to the band gap. THis added load may be causing a systematic offset in your bandgap. If you simulate the bandgap just with the resistor network does the voltage go to 1.4V? If this is the case, you can buffer the bandgap voltage with a unity gain buffer. THis would elminate the loading effects.

I have implemented weak inversion bandgap reference topology, when i i have connected resistor as load at output of bandgap reference from 100 ohm to 1k ohm . then reference voltage gets drop down from 1.26v to certain millivolt.but when i connect it with error amplifier it will g to 1.4 v .

i got ur point but i need some more clarification about it from you. is there any problem in error amplfier ...? i thought it is loading problem of BGR.
give reply ASAP...

thanks for co-operation.

Added after 11 minutes:

here is my circuit topology is based upon weak inversion bandgap reference, tell where to connect UGB here

hi if somebody know how t resolve this issue then please give reply very soon. i think i can use unity gain buffer to resolve this issue. but how do i list spec for UGB and which kind of topoloy used....
please give reply i need to know deseperatly

 

[rachel607]

Re: Question about LDO and Bandgap Reference help me if u ca

negative feedback is necessary when connected and loop gain is important.
BTW, how could you make sure weak inversed MOSTs work well? Could the process do it?

 

[w98211012]

Re: Question about LDO and Bandgap Reference help me if u ca

negative feedback is necessary when connected and loop gain is important.
BTW, how could you make sure weak inversed MOSTs work well? Could the process do it?

yes, i agree with you. negative feedback shoud be needed. And the bandgap is a open system, so ur bandgap may be unstable. u shoud change ur bandgap circuit.

regards!