TPS63020-Q1: start up time

The startup time depends on a lot of parameters including the supply voltage and the output impedance of the power source and cannot be easily predicted. You can get an indication of the timing and its variation in Figure 16 or Figure 17 in the datasheet.

Hi Juergen,

Thank you for your reply.

I understand that the startup time(i.e. the ramp up time of Vout) depends on a lot of parameters.
However the delay time between start point of switching and UVLO of VIN is defined at inside the IC. Is this correct? Can you provide that delay time if it is so?

On the other hand, if it is not so, what is the delay time(between UVLO of VIN and start point of switching ) depends on?
Because in Fig 16 and Fig 17 that delay time seems the different each other.

Regards,
Koji Hamamoto

I think both pictures show a similar delay time of about 50us, just the time resolution is different. But it is not related to UVLO, it is related to EN going high. In case of UVLO it should be similar, but I would expect that due to the low voltages at the time the device starts to operate the startup would be slower.

Hi

I am sorry. I have missed the time resolution.
As you mentioned, it is not related to UVLO , however we can estimate it is about 50us. (Only in this case.)

>but I would expect that due to the low voltages at the time the device starts to operate the startup would be slower.

Does it depend on VIN and VINA voltage?

I think the ramp up time is difficult to predict because of the lot of parameter is related. However at least we need to estimate that delay time at low voltage. Can you provide that time and its variation at low voltage (as a worst case)?

Regards,
Koji Hamamoto

I don't think the delay time varies much with the supply voltage, but the available energy at the input does. So I would expect the worst case for startup at the lowest input voltage you can have in your design. I would suggest to take startup measurements in your system and use the results, adding some margin.

Hi Juergen,

Thank you for your reply.

I found the waveform on the application note of TPS63020EVM-487.

At figure 1 shows that the delay time is about 4ms between EN and start point of Vout. 

( It is different very much from datasheet(=50us).)

http://www.tij.co.jp/jp/lit/ug/slvu365/slvu365.pdf

I understand that the ramp up time of Vout depends on many parameter (as you mentioned). However I do not know how can we estimate the internal delay time which is between EN(or VIN UVLO) and the start point of Vout (=start to switching).

Regards,

Koji Hamamoto

I think this is just a nice example for the dependency of the startup time on many parameters. The picture shows a startup into an electronic load. I guess that the control circuit of the electronic load defines the curves and the timing.
The built in startup sequence in the device causes a delay of about 50us from EN going high to starting switching. As soon as the device starts switching all control features for protecting the device are active and can define the behavior of the device (section 9.3.2 and 9.4.1 in the datasheet) depending on what is connected at the input and at the output of the device.

Hi Juergen,

Thank you for your reply.

>The built in startup sequence in the device causes a delay of about 50us from EN going high to starting switching. As soon as the device starts >switching all control features for protecting the device are active and can define the behavior of the device (section 9.3.2 and 9.4.1 in the >datasheet) depending on what is connected at the input and at the output of the device.

I understand your explanation. After start the switching it has the dependency of the startup time on many parameter.(as you mentioned and section 9.3.2 and 9.4.1)However my point is about the delay time of before start the switching.

Especially , how that delay time will be when the EN is tied to VIN. I think the device will start to operate when the VIN is exceed the "Minimum input voltage for startup ". (EN threshold is lower than VIN threshold. It depend on VIN in this case.)
Then it has the delay time(50us) same as when EN is tied to VIN. Is my understanding correct?

It will be ok if delay time will be enough shorter than ramp up time. Our concerns is that delay time (of before start the switching ) will be longer unexpected.(e.g. a few ms or more)
* I don't understand why the Figure 1(above picture) has taken so much delay time... I think EN must be tied to VIN at that configuration .

I am sorry for the long questions.

Regards,
Koji Hamamoto

Hi Juergen,

I am sorry for the delay in my response.

I suggested to the customer what you answered. I hope this answer can help the customer concerns.
(Regarding your curious question , I think that delay is no problem if the delay including worst case variation is enough shorter than ramp-up time. However it will be concerned if the delay has possibility to be more than 50us or a few msec.)

Please close this issue. ( I will ask again if I get the additional question from the customer.)

Thank you for all your help.

Regards,
Koji Hamamoto