TPS259230/40 over current limit behavioH1

JeffYC Yang

Hi,

I have some question as following.

1. If TPS259230/40 over current limit set at 5.1A(TPS259240 Rilim=150k), if take a load 6A at loding side, it will limit at 5.1A, but not cut off the internal MOSFET? right? Or it will cut off internal MOSFET?

2. Is it possible trigger OCL when hot plug with a big inrush current? Or it have soft start so won't have a inrush current?

3. As Q1, if OCP cut off internal MOSFET, it based on choose TPS259240/1, protect behavior is latched/auto retry?

Thanks!

Jeff

over 8 years ago

0 Rakesh over 8 years ago

TI__Guru** 105361 points

Hi Jeff,

Q1. with current limit setting (Rilim=150k), the device can limit currents any where from 4.5A to 5.7A as mentioned in the datasheet. Depending on the amount of overload, the device may cutoff the internal FET due to thermal shutdown.

Q2. The device limits inrush current for hot plug events and provides soft start. The inrush current can be controlled by selecting suitable dVdT capacitor. Please use the design calculator available on the web.

Q3. In overload condition, the device may cutoff the internal FET due to thermal shutdown. A latched part TPS259240 remains in OFF position where as auto retry part TPS259241 attempts to start after 100us time interval.

Regards,
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

Thanks for the Q1/Q3 reply firstly.

As your Q2 reply,

If TPS259230/40 in turn on state, but suddenly drain a big current from loading side as datasheet figure33, it seems cut off at 12A/20ns,

How do I know this kind of load fast transient current trigger OCL or not? If 12A but only during 5ns? or 15A during 1ns? Have any specification define the trigger condition?

Thanks!

Jeff

0 JeffYC Yang over 8 years ago in reply to JeffYC Yang

Expert 1290 points

Hi Rakesh,

I have another question about the datasheet figure.32, it seems already cut off, but why still have about 4A loading?

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

The device incorporates fast-trip comparator to respond fast for transient short circuit events. The set threshold is at 1.6 times the current limit value. For example, if current limit is set at 5A, the fast trip comparator acts only if fasting changing load current exceeds 8A and turns OFF the internal FET in around 200ns. The trigger condition is 1.6XILIM.

Regards,
Rakesh

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

The fast-trip comparator turns OFF the FET immediately to avoid any damage to the device. But these spiky transient currents may not be the real faults, so the device starts in current limit mode after fast-trip cutoff.

So, in this case, the device starts again in current limit mode and limits output current to 5A.

Regards,

Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

Thanks your reply, it big help to me and my customer.

0 JeffYC Yang over 8 years ago in reply to JeffYC Yang

Expert 1290 points

Hi Rakesh,

My customer have another question as following.

1. They meansure that sometimes have suddenly inrush current have 15A/10us, but no trigger OCP. As your reply before it should be trig at 1.6 * ILIM/200ns. Do you have any idea about this?

2. Does TPS259240/1 OVP behavior is the same? If there have 20V in, both TPS259240/1 are clamp output voltage at 15V?
So TPS259240/1 only different at OCP behavior? right?
And how about TPS259240/1 UVP behavior, both TPS259240/1 UVP behavior is the same?

Thanks!
Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

Q1. Can you please share the test waveform and test conditions.

Q2. Both devices TPS259240 and TPS259241 gets turned OFF after fault. The only difference between them is recovery after fault. TPS259240 remains in OFF position and needs Vin or EN reset to restart the device where as TPS259241 attempts to restart after 100us.

Best Regards,
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

Please refer to following waveform, Iout peak~15A/12us.

TPS259231/41 have possible to auto retry frist 3 times OCP, then latched at the fourth time?

Or have other solution can meet this OCP behavior?

Thanks!

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

Load current measurement exactly does not reflect the switch current. When the device is turned OFF, the load current component also has output capacitor discharge current. Measuring at the points mentioned in below figure gives appropriate indication on Fast current trip threshold and response as this is the actual switch current which devices is measuring.

Regards,

Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

I'm clarifying peak current measure method is correct or not with cutomer, could you please help to reply below question?

"TPS259231/41 have possible to auto retry frist 3 times OCP, then latched at the fourth time?

Or have other solution can meet this OCP behavior?"

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

Do you want a device which auto retry for first 3 times for an OCP fault and then latch OFF if it continues to fault? If this is the requirement. Currently we do not have product to meet this behavior.

Regards,
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

My customer still want you provide more detail and formal OCP trigger condition, could you please also provide maximum and minimum? They more concern about "around" this wording.

"load current exceeds 8A and turns OFF the internal FET in around 200ns"

Thanks!
Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

The minimum current where fast-trip starts trigger is 1.6 times the set current limit value.
As mentioned above in the application schematic, measuring the switch current provides correct information where exactly the switch is getting turned OFF. Because the peak load current magnitude and di/dt are determined by the circuit parasitics, impedance of short, capacitance at the output terminals.

Can you please check with the customer the exact requirement and the application.
If required we can plan to have a discussion with the customer.

Regards,
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

We now meet unexpected OCP lactched, so we want to clarify more detail on OCP trigger conditon.

About I-fast-trip we have been clarify, but continue OCP trigger timing could you please share more detail.

How will trigger continue OCP?

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

I would propose to have call with you & customer to close this issue.
I have sent you the details

Thanks
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

Actually I'm not good at phone convensation, could you please share the continue OCP trigger timing detail by wording for me?

Thanks!
Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

TPS2592XX family of eFuses has two kind of current protection corresponding to overload condition and short circuit condition.

Response to output overload event.

For example, if you set RILIM = 45.3 kΩ the device sets current limit ILIM to 2.1A (typ). If load current increases but less than Fast-trip threshold (1.6*2.1 = 3.36A typ), the device will regulate the output current between 1.79A to 2.42A. If overload event still exists at the output, the device will enter into thermal shutdown.

Response to short circuit event.

For example, if you set RILIM = 45.3 kΩ the device sets current limit to 2.1A (typ). For a short circuit at the output, the load current increases more than Fast-trip threshold (1.6*2.1 = 3.36A typ), the fast-trip comparator acts to turn OFF the internal FET. The fast-trip comparator turn-off delay is 300ns (typical). So, in this time delay, the FET current may go even higher depending on circuit conditions.

The FET current and Iout current are different when the device is turnoff. The output capacitor also feeds the short circuit path. so, the lout peak/duration will depend on output capacitor. Please monitor the input current or FET current to get the timing details for short circuit event.

Regards,

Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

We are understand the short circuit event how to work, but our question is your description for "Response to output overload event. "

Response to output overload event.

It have no trigger time descrption, for short circuit event, it trigger by reached 1.6xILIM, but how about the output overload event?

If set RILIM = 45.3k, now load current over 2.42A, but less than 1.6x2.1= 3.36A, how long will let TPS259240 into thermal shutdown? If an inrush current only few us?We want to know the trigger time threshold.

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

The device will enter into thermal shutdown based on the power dissipation across internal FET during overload condition.

Let me explain with an example for overload case.

Vin=12V, Rilim = 45.3K, Let's say you placed load resistor 4ohm which causes load current 3A at 12V output.

Now the device tries to regulate load current to 2.1A (typical value corresponding to Rilim = 45.3K). So, Vout = 2.1A*4ohm = 8.4V

Power dissipation across internal FET = (Vin - Vout) * Iout = (12-8.4)*2.1 = 7.56 W. Based on the below thermal shutdown plot, the device will shutdown in 20ms time.

0 Rakesh over 8 years ago in reply to Rakesh

TI__Guru** 105361 points

Hi Jeff,

for the above case, 20ms shutdown time is at ambient 85degC.

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

So, If I meansurement as below:

Trig OCP current = 5.46A, Vin=12V,

Rload= 12V/5.46A= 2.197ohm, Vout = 5.1A(Rilim=150k)*2.197 = 11.2V,

PD= (12V-11.2V) * 5.46A = 4.368W, mapping to Figure40 table, in TA=25C, it need about 2000ms = 2s to trigger thermal shutdownm, right?

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Correct!

Regards,
Rakesh

0 JeffYC Yang over 8 years ago in reply to Rakesh

Expert 1290 points

Hi Rakesh,

My customer still found OCP trigger by

0 JeffYC Yang over 8 years ago in reply to JeffYC Yang

Expert 1290 points

Hi Rakesh,

My customer still found OCP trigger by below waveform, Vin= 12V, Iout= 5.56A, Rload= 12V/5.56A = 2.158ohm, Vout= 2.158ohm* 5.1A= 11V

PD = (12V-11V) * 5.56A = 5.56W, It need 500~600ms to hit the thermal shutdown. But in below waveform, it only ~3.6ms.

Do you have any idea about this?

Thanks!

Jeff

0 JeffYC Yang over 8 years ago in reply to JeffYC Yang

Expert 1290 points

Hi Rakesh,

We also try to used customer MB and EVM test as below condition:

Load: 12V dynamic load, 2A/2ms, 5A/2ms, find it will tirgger OCP, is it make sense?

(Due to back end device when during boot up process, average 2A loading, sometime load a peak to 5A, we found it may cause TPS259240 latched)

If possible, could you please arrange time have a con-call with my customer? or take a business trip to Taiwan?

Thanks!

Jeff

0 Rakesh over 8 years ago in reply to JeffYC Yang

TI__Guru** 105361 points

Hi Jeff,

I will take this discussion via email along with your customer.

Thanks and Regards,
Rakesh

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TPS259230/40 over current limit behavioH1