TPS7H2201-SP: 22A fast trip capability

Hi Michael, 

Michael T Schneider said:

In looking at the data sheet, it looks like the 22A fault protection during a fault, holds at 22A for 15 to 35uSec, turns off for 61 to 158 uSec and then tries to turn on again? I am I right? Also when the TPS7H2201-SP comes up again does it ramp up with the slew rate it is set at?

Firstly, to your questions regarding fast trip timing and restart slew rate: yes, that's correct.

Secondly, the timer questions. Connecting Rtimer to ground means that once the device is disabled, it will remain disabled until the EN pin is cycled. The only way for the device to attempt to reset itself after becoming disabled is to use a capacitor on the Rtimer pin.

Connecting ILtimer to ground without a capacitor will cause the device to remain in current mode once it has entered that mode until the EN pin is cycled. Connecting ILtimer to Vin will cause the device to use an internal timer (15 μs typically, but up to 35 μs max) instead of the programmable timer (which can be set by the user with a capacitor placed between the ILtimer pin and ground). If the fault is removed before the internal timer expires then normal operation will resume, otherwise the device will be disabled until the EN pin is cycled.

Finally, your question about the length of the programmable timer, ILtimer. You can determine the length of ILtimer for a given capacitance using this equation (t in μs, C in pF): 

t = C/2

You will need to consider the tradeoffs of each scenario and decide which features (self-restart, fewer capacitors, etc) are most important in your design.

Hope this helps,

Sarah

Hey Michael,

Am I correct in interpretting "latched off" to mean that the device remains disabled until cycling EN? If so, connecting Rtimer to ground should have that effect. 

While that is the correct value of RIL for setting the programmable current limit to 3A according to the datasheet, you should keep in mind that the programmable current limit is ±20% accurate. This means that it could actually be as high as 3.6A or as low as 2.4A. If you do not want to allow more than 3A then it is better to calculate RIL for 2.5A.

Just to be clear, the internal current limit timer is different from the programmable current limit timer. It is a set value defined by the datasheet (15 μs typically, but up to 35 μs max), whereas the programmable current limit timer is set by connecting a capacitor between the ILtimer pin and ground. Note that the capacitor should not be connected between ILtimer and Vin. The ILtimer pin may be connected to Vin (no capacitor) if the user desires to use the internal timer instead of the programmable one. 

I'll get back to you about this sentence: "When using the internal timer, only the fast trip off current limit is active."

Hi Michael,

Sarah Koch said:

I'll get back to you about this sentence: "When using the internal timer, only the fast trip off current limit is active."

This statement is meant to express that when ILtimer is connected to Vin, the fast trip current limit (22A) will remain accurate as stated in the datasheet. However, the internal timer is quite short so the accuracy of the programmable current limit (based off of RIL) cannot be guaranteed in the same way since it does not have time to settle to the programmed value. 

Connecting Rtimer to ground and ILtimer to Vin would result in the behavior shown in Figure 27 of the datasheet: a 22A fast trip followed by brief current limited operation. If the short is still there when the internal timer expires then the device will be disabled until EN is cycled.