This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Part Number: TPS51116
could you tell me why does IC set the over current as half of nominal value ?
> 8.3.9 Soft-Start Function and Powergood Status The soft-start function
> of the SMPS is achieved by ramping up reference voltage and two-stage
> current clamp. At the starting point, the reference voltage is set to
> 650 mV (87% of its target value) and the overcurrent threshold is set
> half of the nominal value. When UVP comparator detects VDDQ become
> greater than 80% of the target, the reference voltage is raised toward
> 750 mV using internal 4-bit DAC. This takes approximately 85 μs. The
> overcurrent threshold is released to nominal value at the end of this period.
The part was released many years ago. I can not find the original design team and ask them why OC threshold is half of nominal during soft start.
Sorry about it.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
In reply to Qian Chen:
Do you think the half of nominal OC threshold is benefit for something ?
In reply to Masaharu Takahashi:
I guess the purpose is to limit the inductor current during soft start, hence limit the Vout slew rate to make Vout rise up smoothly.
do you see that IC works properly by seeing below pic?
The Vout waveform looks fine.
There is a spike on inductor current at the end of soft start. I guess it is from load current.
the amount of current IC limits is the overcurrent threshold is set half of the nominal value.
but it seems IC didnt shut down even the current hits the half of current.
could you tell me why?
The over current protection only does cycle by cycle current limit. It does not shut down rail directly.
During steady state, if there is over current situation, the Vout will drop and rail will shut down when Vout drops below UV threshold.
Vout UV is enabled after 1007 switching cycle. Please refer to datasheet section 8.3.13 on page 24.
As UV is not enabled during soft start in your waveform, the rail does not shut down.
could you tell me below 2 more question my customer asked.
for 1007 cycle you mentioned , does "each cycle in 1007" mean 2.5us(400kz frequency)?
Q2.let me confirm below
will the UVLO be enabled in 1007 cycle once the amount of current hits the current threshold, correct?
1. Each cycle means 2.5us if Fsw is 400kHz.
2. The Vout UV protection will not be enabled during 1007 cycle. It is only enabled after 1007 cycles.
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.