TPS54140: SoftStart Time

Brian Wang0928

Genius 14160 points

Part Number: TPS54140

Hello,

There are two questions about TPS54140 soft star. Could you help on this inquiry! Very thanks.

1. In the 9.2.2.6, it says the avg. input current to be 0.125A. Where does this current come from?

2. What period is for the soft start time from below waveform Figure 29?

over 5 years ago

0 Gavin Wang (Zejing) over 5 years ago

TI__Expert 3480 points

Hi Brian,

1. This current come from the IC. The value is set by yourself, which should be smaller than current limit.

2. It is 20ms/div. You can read from the picture.

Gavin

0 Brian Wang0928 over 5 years ago in reply to Gavin Wang (Zejing)

TI__Genius 14160 points

Thanks. Double confirm with you.

1. Do you mean that the input avg. current that is going trough the MOSFET in side of device? and it is sets by the Css(soft star cap) value?

2. The Sotstar time is 40mS around as Fig29, right?

Regards

Brian

0 Gavin Wang (Zejing) over 5 years ago in reply to Brian Wang0928

TI__Expert 3480 points

Hi Brian,

1. Yes, the input avg. current that is going trough the MOSFET in side of device. But it is sets by the high side MOSFET current limit. Not the soft start cap.

2. The Sotstar time is 40mS around as Fig29, right? Yes.

Regards

Gavin

0 Brian Wang0928 over 5 years ago in reply to Gavin Wang (Zejing)

TI__Genius 14160 points

Thanks.

In the example of the d/s, i wanna to know how to determine the 0.125A? Could you help on this for customer's design review! Very thanks.

0 Marshall_Beck over 5 years ago in reply to Brian Wang0928

TI__Mastermind 35210 points

My thought is to be it is related to peak output current limit of the device somehow.

Please let me follow up.

0 user6237377 over 5 years ago in reply to Marshall_Beck

Prodigy 10 points

Hello

1. can you have any response for input current =0.125A? what ralationship between the input current and peak output current?

I calculate this value for application note example circuit, use input power equal to output power (Vin*Iin= Vout*Iout) is 0.275A? what are you think this?

2. otherwise, can you provide the switching frequency fsw(max skip) and fsw(max shift) the curve (Figure 41) for Vout=5V and Vout=12V?

or in Figure 41's curve, what value for equation 12&13? (IL, Rdc, Voutsc, Vc, RDSon, ton(min), fDIV ?)

3. for compensation design, if over the suggest range for equation 43 44 45 46, have any problem in application?

0 Brian Wang0928 over 5 years ago in reply to Marshall_Beck

TI__Genius 14160 points

Please help on the questions. thanks.

0 Marshall_Beck over 5 years ago in reply to user6237377

TI__Mastermind 35210 points

Hello,

Is there a particular issue you are attempting to resolve in your system, or are we trying to figure out the schematic entry for this device?

To jumpstart your design, we have an already validated schematic design for TPS54140.

Please see the userguide for TPS54140 EVM which contains the validated schematic, as well, application curves to demonstrate device performance.

http://www.ti.com/lit/ug/slvu285/slvu285.pdf

The EVM is orderable on TI.com for a reasonable price, such that, device performance can be verified on your bench.

Let me know if this helps.

Power management

Power management forum

TPS54140: SoftStart Time