UCD3138: How to use ramp up for SR soft on

liwei qi

Part Number: UCD3138

In datasheet,it said that:"One solution to this issue is to ramp the voltage up to the target without synchronous rectification (SR), and then to activate SR after the voltage is regulated. When activating or deactivating
SR, in order to avoid glitches in the regulated voltage, it is best to gradually increase/decrease the Sync FET on-time."

About the operation , I have some question:

1. If use front end2 to ramp up, How to set the value of RAMPDACEND.RAMP_DAC_VALUE? the output target voltage?

2. only accomplish SR soft on, it need to enable the bit of IDE_DUTY_B_EN in DPWMCTRL2?

over 3 years ago

0 Sean Xu over 3 years ago

TI__Genius 14580 points

Hello, Liwei,

I believe you can find the example code from UCD3138HSFBEVM029 EVM firmware available on ti.com. Frontend 2 ramp module can do SR soft on without setting the bit IDE_DUTY_B_EN. RAMPDACEND.RAMP_DAC_VALUE has 4ns resolution.

Regards,

0 liwei qi over 3 years ago in reply to Sean Xu

Expert 1160 points

Hi,Sean:

I had found the firmware of UCD3138HSFBEVM029. In the firmware, the IDE function need enable when define IDE_ENABLE. I do not open IDE function and try to test the SR soft on with ramp up . It is not ok.

So i ask the question above.

0 Sean Xu over 3 years ago in reply to liwei qi

TI__Genius 14580 points

Hi, Liwei,

If you use front-end ramp module

Dpwm0Regs.DPWMCTRL1.bit.SYNC_FET_EN =1;

Dpwm1Regs.DPWMCTRL1.bit.SYNC_FET_EN =1;

Go to void init_loop_mux(void) to find the initialization.

IDE_DUTY_B_EN need be enabled for firmware ramp up.

0 liwei qi over 3 years ago in reply to Sean Xu

Expert 1160 points

Hi,Sean:

Thank you!

if enable the bit of IDE_DUTY_B_EN, How can i set the value of DCM_LIMIT_H and DCM_LIMIT_L? Do you have method?

0 Sean Xu over 3 years ago in reply to liwei qi

TI__Genius 14580 points

Hi, Liwei,

You may set DCM_LIMIT_H and DCM_LIMIT_L as the period so that they don't go beyond the period. The DPWMB duty is changed by FaultMuxRegs.IDECTRL.bit.IDE_KD.

0 liwei qi over 3 years ago in reply to Sean Xu

Expert 1160 points

Hi,Sean:

Thank you for your help! I have achieved the function of SR soft on with ramp up without disable IDE.

But I have a problem when SR soft on, the output voltage have shake.

0 Sean Xu over 3 years ago in reply to liwei qi

TI__Genius 14580 points

Hi, Liwei,

It is normal because it is in DCM mode before SR finishes ramping up.

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UCD3138: How to use ramp up for SR soft on