TPS62130 TOFF time

I'm not sure that I understand your question. DCS-Control is controlling the on time. For any buck converter, the duty cycle is given by Vout/Vin (ideally). So, if duty cycle and on time are given, then off time is simply the resulting time during 1 period. It is not controlled directly.

Hi chrisFrom datasheet p10 Figure.19,Vin:Vin<6VVout:3.3V
When tihs condition,SWF is down.
I measured at TPS62130EVM,Fixed TOFF=130ns and TON had longer.
But datasheet not written TOFF time.At the time of this condition,
I want to calculate how much the frequency to change. RegardsT Kishi

Thank you for clarifying.  Yes, the frequency in figure 19 decreases for 2 reasons: higher drop across the high side MOSFET and a minimum off time.  At lower Vins, the Rdson increases a little bit, so the on time must be extended to overcome these losses.  This will decrease the frequency since the on time must be longer than expected.

At higher duty cycles, you will see a ~130 nsec minimum off time which also decreases the frequency for very high duty cycles.

The output remains regulated in both cases and there is no issue operating in this region.  Using the 1.25 MHz frequency setting will make the variation from the minimum off time have a smaller effect on the frequency.

Is this an issue in your application?  What power specs do you need to meet?

Hi Chris Thank you for reply.There is no problem at chang of frequency.
How much value I wanted to calculate what would change.
I know that it Minimum TOFF time is 130ns,It is possible to estimate the frequency in the approximate calculation.
Thank you!Best Regurds

The simplest way would be to measure it. But a calculation should be fairly straightforward. Since the off time is 130 nsec and your duty cycle is known (from Vout/Vin), you can estimate it from this formula: f = (1-D)/130nsec from toff = period * (1-D). The duty cycle will likely be larger than expected since this behavior occurs at lower Vins where the Rdson is higher and duty cycle loner.

Hi Chris

Thank you for reply.

I want to one question.

Change the FB resistance(R1) of TPS62130EVM, Vin=3.3V, Vout=2.0V, Duty=60%, Iout=500mA, SW=2.5MHz

If this condition,PWM mode should operate at 2.5MHz.

But check the waveform,SW=about 1.5MHz

ON time=480ns,OFF time=240ns (fix)

I want you to tell me why this happens

Regurds

T kishi

Since you are using a wide Vin IC at such a low Vin, several internal timing circuits shift. A lower frequency is expected here.

If you have a 3.3V source, the TPS62090 would be a better device.

Sorry,I can't change the device.
If it is this condition,How much of it can not be assumed become frequency?

I'm sorry but I do not understand your question. Can you rephrase it?

When Vin is low,several internal timing circuits shift.
Timing is shifted from how much low Vin?

As figure 19 shows, this begins around 6Vin.

Hi Chris

I want to point out me, if i think is different.

I think Off time is Fixed,When around 6Vin.And Off time is diffrent by Vout.

ex)Vin=6.0V  Vout=1.26V Off time=about 120ns
   Vin=6.0V  Vout=2.0V    Off time=about 220ns

 I was measured ins this condition.

    Vin=4.0V Vou=1.26V  Off time=about 120ns
    Vin=4.0V Vou=2.0V  Off time=about 220ns

Therefor,Frequency begin around 6Vin,Off time of when the diffrent by Vout.

if match my guess is,the problem become clear.

Regurds

T kishi

Hi ChrisThank to you！Problem become clear！Best RegurdsTkishi

Hi Chris

This problem,described my customer.

So ther is a request,Do you have any infomation such as Application notes or Documents on this issue?

I would like to have if there is material.If not ,to negotiate to my customer.

Best Regurds

T Kishi

Besides what is in the D/S, this app note discusses DCS-Control: http://www.ti.com/lit/an/slyt531/slyt531.pdf

Your local TI Japan FAE should have access to some training presentations we've given on DCS-Control over the years.