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LM5170-Q1: LM5170-Q1 Simulation

RAYEES K E
Intellectual 320 points
Part Number: LM5170-Q1
Other Parts Discussed in Thread: LM5171-Q1, LM5170, LM5171

Tool/software:

Hi,

I was doing the simulation in Tina for 2 phase buck converters with below specifications, 

Input: 15.5V

Output: 14.7V (Output voltage with Maximum Duty)

Load current: 60A (30A per phase)

Frequency: 100KHz

Using the External voltage loop.

I have seen with the above specification the simulation results are not proper, the overall current is not dividing to both the channel, Channel 2 is loading with 90% of the current and waveforms of channel 2 is not proper.

The same is checked for by increasing the input voltage, 18V input and 14V output, its working properly. But 16V and below input the problem is happening.

Please provide your feedback.

Our actual Design is with LM5171-Q1 for 4 phase Buck converter with maximum output of 125A. For the simulation purpose using the LM5170-Q1.

Attached the Tina files and the Design calculator as below,

DCDC Buck_18th Nov24 - Copy for TI.tsc

LM5170_DESIGN-CALC_V1.1.0.xlsx

Regards

Rayees K.E

  • 0
    TI__Mastermind 24820 points

    Hi Rayees,

    Current may not increase to the required level if the maximum duty cycle is reached.

    LM5171 has higher maximum duty cycle compared to LM5170. And still, you may need to reduce the switching frequency to get higher duty cycle.

    Best Regards,

    Feng

  • 0 in reply to Feng Ji
    Intellectual 320 points

    Hi Feng,

    Thank you for your response.

    As per the datasheet the maximum Duty for LM5170-Q1 is,

    Dmax= 1-(200nS+56nS) *100K=0.97    With 10K DT resistor and 56nS Dead time.

    I am operating at 15.5V input and 14V output, ie Duty=14/ (15.5*0.95) =0.95

    So, i am not reached the maximum duty cycle limit of LM5170-Q1.

    Our concern is whether this Duty cycle limitation is only for simulation with LM5170-Q1 or practically how much duty cycle we can consider for LM5171-Q1. 

    We will be operating at 100KHz frequency, and Input is 15.5Vdc, and targeted output 14.5V minimum, load current 125A for with 4 phase operation.

    Please clarify, how much we can target the output voltage with 15.5V input.

    For LM5171-Q1, as per the datasheet the maximum Duty is,

    DMAX = 1 − 150ns + tDT × Fsw

    Dmax= 1- (150nS+56nS*100KHz) =0.979

    Regards

    Rayees K.E

  • 0 in reply to RAYEES K E
    TI__Mastermind 24820 points

    Hi Rayees,

    It is diffcult to tell the exact duty cycle in your application. It increases with the resistance of the inductor, MOSFETs and so on. You may need to run a simulation with these parameters.

    Best Regards,

    Feng

  • 0 in reply to Feng Ji
    Intellectual 320 points

    Hi Feng,

    Thank you for your support.

    As per simulation, Maximum duty i am able to simulate is 0.85 only.

    Hope, with original part LM5171-Q1 we can go higher duty.

    Regards

    Rayees K.E