Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Buck feedback loop with high gain to current sense.

cupoftea

Advanced Member level 5
Joined
Jun 13, 2021
Messages
2,660
Helped
54
Reputation
108
Reaction score
116
Trophy points
63
Activity points
13,984
Hi,
Doing Synch Buck for 27Vin, 13V out, 15A out and 450kHz.

LTpowerCAD is showing the gain Bode plot curving back up to the 0dB line at higher
frequency than the crossover. - Which means instability.
As such, wish to make out own Bode plots.
Can get the Power stage transfer function for a current mode CCM Buck.
Can get the Transfer function for the type 2 transconductance error amplifier.
However, can you confirm that the controller gain means that we will have to multiply in
the factor of 1.4V/0.075V for the attenuation regarding the peak current threshold (75mV)
and the maximum control voltage, which appears to be 1.4V?


Graph on top left of datasheet page 7 appears to show the controller gain, by way of V(ITH) vs Current sense voltage

LTC3891 datasheet
 
Last edited:
Hi, The LTC3891 datasheet unfortunately doesnt give the current sense gain. ie, the amount by which the current
sense voltage is multiplied, so as to increase it. Due to this, it is not possible to calculate the
transresistance for any Buck converter made with LTC3891...and because of that, its not possible to do a Bode Plot
calculation for the LTC3891, because the transresistance is a needed parameter in the calculation of the control to output transfer
function.
As you know, the transresistance is the voltage coming off the sense resistor divided by the current that caused it by flowing through it.
As such, do you know how we can find out the current sense gain for the LTC3891?

They have LTpowerCAD but sometimes its good to have your own checker...specially since you can extend your own to include any output LC filters added in.
 

LaTeX Commands Quick-Menu:

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top