error amplifier design for SMPS (buck converter)

Thread Starter

arunkps

Joined Jan 28, 2014
16
Hi,

I am designing a synchronous buck converter & the specs are as follows:
Vin = 1.8V
Vo = 0.5V
Io = 1mA
Fsw = 1Mhz
Vripple(p-p) = 500 micro volts

For this I need to design error amplifier. My understanding is that I need to design a two stage op-amp with input differential amplifier followed by a common source amplifier. I read multiple sources for designing a two stage opamp but I did not get the grip. I am confused how to choose the specifications like input swing, Bandwidth, gain, required output voltage from error amplifier. Please help me to design a error amplifier and a suitable compensation for my project.
 

AnalogKid

Joined Aug 1, 2013
9,244
Why in the world do you want to use a switching power supply for an output power of 0.0005 W? There is no switcher topology that will do this. You could do it with a linear regulator, but again - why? I guess you could use a 470 ohm resistor and two shottkey diodes stacked up to form a low-voltage zener, but there's no adjustability there. You don't have to worry about power dissipation in a shunt regulator because the total circuit power (regulator + load) would be only 5 mW. AND - no ripple.

ak
 

Thread Starter

arunkps

Joined Jan 28, 2014
16
Hi,

Basically I am doing my project on buck converter. The specifications are chosen by myself with no specific technical considerations. May be that is the reason I did not notice the very low output power requirement. Thanks for mentioning that. My objective is to design a synchronous buck converter. Now as you said I will change my specification & increase my output current.

Can you help me to design an error amplifier?, I hope the output current will not affect the opamp specs much. My concern is I am wondering how to chose the specification for the error amp like the gainbandwidth, input swing,output swing, slew rate etc...,
 
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