Smart high side switch is a 200mA current clamp device?

[treez]

Hi,
Would you agree that the BTS4140N clamps the current to 200mA?
Also, that the clamp current is not settable?

BTS4140N

https://www.farnell.com/datasheets/2333304.pdf

 

[KlausST]

Hi,

Please read the datasheet.

200mA is the nominal load current.
Clamp current is somewhere between 200mA and 1200mA

Klaus

 

[treez]

200mA is the nominal load current.
Clamp current is somewhere between 200mA and 1200mA

Thanks, but if the nominal load current was controlled to be 200mA......then that would also be the clamp current surely?

The "initial peak s/c current" can be anywhere from 0.2-1.2A.

I am still not sure though

 

[KlausST]

Hi,

The nominal 200mA are not controlled in the meaning of "regulated" or "limited" by the device.
It says you should use load that normally draws not more than 200mA.
Example: On a 12V system the load resistance should be more than 60 Ohms.

Then in case of an error the current may be higher ... then the device protects itself by limiting the current to a safe value.
200mA ... 1200mA.
The limiter should be active in case of an error only, not during normal operation.

Klaus

 

[stenzer]

Hi,

as fare as I interprete the datasheet it depends on the temperature, by means when the thermal overload trip temperature \[{T}_{ jt}\] is exceeded. Have a look at the protection function values on page 5. The initial peak short circuit current is stated for three different temperatures, where the 1.2 A is valid for the lower end of the operating temperature range of -40 °C (best cooling of the device). So I would say the maximum initial peak short current at 25 °C is 0.9 A. Also have a look at page 17, which shows the switching behaviour dependence of the junction temperature.

If you are looking for a more versitale solution, I can recommend the TPS1H200A-Q1 [1], which offers a dedictaed current setting as well as different over-current behaviours.

[1] **broken link removed**

BR

 

[treez]

It says you should use load that normally draws not more than 200mA.

Thanks, i kind of thought this too...but i cannot find anywhere in the datasheet where it insists that one should try to limit current to below 200mA.

Its hard to tell......if the IN pin is left floating, then the internal power switch is OFF?

The limiter should be active in case of an error only, not during normal operation.

A contractor has done a schem where he uses the BTS4140N to do battery charging from a voltage rail that is variable from 13V to 9V.
I am trying to figure out how he knows what current the BTS4140N will regulate to?
As you kindly say, the current limit seems to be variable dependent on temperature.

 

[stenzer]

Hi,

Its hard to tell......if the IN pin is left floating, then the internal power switch is OFF?

by having a look on the block diagram on page 2, I would asume it is turned-off if the in pin is floating. This is further indicated by the "Inductive Load switch-off energy dissipation" descriped on page 11.

... will regulate to?

to my understanding the PROFET does not regulate the current directly (I do not see any indication of current sensing in the block diagram), it is protecting itself by means of an temperature hysteresis. So there is no regulation to a certain "target" current as this is also a function of the ambient temperature i.e. higher maximum allowable constant current at low temperatures and a lower constant current at high temperatures. Have a look on page 17 in the datasheet.

A contractor has done a schem where he uses the BTS4140N to do battery charging from a voltage rail that is variable from 13V to 9V.

- Which kind of battery?
- Is there any additional charging strategy implemented?
- Is he using the PROFET to protect the circuitry against a malefunction of the battery by means of a short circuit of the battery, which would lead to a turn-off of the PROFET?
- Or, The PROFET is used to limit the maximum allowable charging current at all. This might be estimated by the intended ambined operating temperature and the thermal resistance of the IC.

This are just a couple of thoughts as it is hard to go any deeper without (at least a sketch of) the schematic.

BR

 

[treez]

Thanks, may we conclude that it would be impossible to draw more than 1.2A through the BTS4140N?

 

[stenzer]

Hi,

for me that is not really clear/obvious. By having a look on the initial peak short circuit current limit on page 5, the 1.2 A are stated for a junction temperature of -40 °C AND a time instance \[{t}_{m}\] of 100 µs. This time is not explained any further within the datasheet, but I assume it is the time instance when this current is measured, after turning on the PROFET into a short circuit. Have a look at Fig. 3a on page 17, where \[{I}_{L(SCp) }\] is "directly" linked to \[{t}_{m}\]. So I assume the actual inital maximum current is higher than 1.2 A at \[{T}_{j}\] = -40 °C.

On the other hand side, the figure in the upper left on page 14 shows an \[{I}_{L(SCp) }\] of about 1 A at \[{T}_{j}\] = -40 °C, \[{t}_{m}\] = 100 µs and \[{V}_{bb}\] = 13.5 V, which seems to cause the highest \[{I}_{L(SCp) }\] according to the figure in the lower left on page 14. So here \[{I}_{L(SCp) }\] is already smaller than 1.2 A at \[{t}_{m}\] = 100 µs.

In my opinion this topic would be worth to address directly to Infineon.

BR

 

[FvM]

Thanks, may we conclude that it would be impossible to draw more than 1.2A through the BTS4140N?

That's what I read from the datasheet. A different question would be if it's advisable to drive the switch permanently into current limiting because it's involving thermal stress and possibly reducing device life time.

 

[treez]

Here is another "smart high side switch"

https://www.infineon.com/dgdl/Infineon-BSP752T-DS-v01_01-EN.pdf?fileId=5546d46259d9a4bf015a8533f0fa778a

...the BSP752.

I am taking it that this device, like the BTS4140N, is just a "dumb" short circuit current limiter...it limits the current to a current level depending on its temperature.....it then switches off when its temperature reaches 150degC, and then switches itself back on again when the temperature falls back below 140degC.....would you agree with this?

 

[stenzer]

Hi,

I would agree, especially by having a look on Fig. 4 on page 14, which shows the temperature tripping behaviour, as shown for the BTS4140N.

BR