It takes 30ms to start boost operation after input voltage to VCC pin (nDIM pin).
Is it correct?
Please let me know if there is any missing information.
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.
Please excuse my lack of explanation.
What I want to know is the device startup delay.
It takes 30msec to enable the device after the nDIM pin voltage exceeds 1.24V.
I want your view on whether this delay time is reasonable.
This depends on where the regulator is at but they all depends on the power stage design. Let me explain things this way.
Let's take for example the case of the Buck-Boost. When VIN is first applied but nDIM is held to less than 1.24V. The GATE (pin 10) will not run so no energy being transferred to the output and VLED differentially will be 0V. Then when nDIM is commanded to above 1.24V, the GATE will start switching and pumping energy to the output stage. VLED differentially will start to rise to the VLED forward voltage and current controlled level. The time it take for this is dependent on external components (inductor, output cap, LED forward voltage ect) but the starting voltage starts from VLED differential of 0V and this takes the longest time.
For the second case, when VLED differentially is at the controlled point with nDIM above 1.24V and then nDIM is commanded low for PWM'ing. The GATE will stop switching and VLED will start to discharge. Depending on how far it discharges to prior to nDIM going high, the time that it take for the current to flow in the LED again is shorter than the first case and can be a lot less than 30mS if the discharge voltage is small. However, this time is still dependent on the external components.
I hope this make helps.
It seems my explanation was not clear enough.
What I want to know is the device propagation delay.
It takes 30ms before the device starts regulation.
The device does not regulate for 30ms.
This propagation delay is considered as a device factor.
I would like you to judge the validity of this delay time.
I do understand your question and I am trying to explain it as best as I can to you here. When nDIM goes above 1.24V the part will start driving the GATE drive with minimal time delay (<10uS) and start charging the output voltage. But current will not flow in the LED if the output voltage is not at the LED forward voltage. The delay from starting to drive the GATE to getting the current to regulate on the LED can be in the mS depending on the output LED voltage and external component.
If you still do not fully understand this then it's probably best that you purchase an evaluation board to better understand the operation here.