VNQ5E160AK 1) current sense limits 2) internal power limitation

JMI · ‎2020-01-07

Hi, I'm using some VNQ5E160AK with current monitoring. According to datasheet Iout/Isense ratio is in the range of 465 for 'high' current, means it should be 6.5mA for 3A and 21.5mA for 10A. As my ADC range is 5V, I load sense pin with a 200 Ohm resistor (=> 4.3V full load).

This work fine at 2.5A (~5mA sense), but don't work anymore with a load at 4A. I believe it's related to Isensh.

To detect power limitation (over load), datasheet tell to charge sense pin with a 3.9KOhm resistor to get 8V, which look strange for me as this imply ~2mA sense and 0.95A load...

Not funny: I use for test a 12V 10A power supply, when I 'overload' output at 8.3A (a 100W bulb), driver burn instantaneously, it even don't try to limit power for overheating (thermal copper area is more than 4cm^2)

Thanks for your help, regards

JMI · ‎2020-01-08

Well, find answer my self reading UM1556: Isense is internally limited to about 11mA by M1, so "no way" to get 21.5mA for 10A. In fact, if you assume a K factor of 465, you won't be able to monitor a current higher than 5.1A ! doesn't matter what you put for resistor load. (it's even worst as K factor decrease with Io).

If you consider case of overtemp, Sense pin becomes a voltage source limited to 8mA, if you want to make difference between 'normal' operation and others, you have to consider 8mA is maximum for normal operation, which (with this 465 K factor) give you a 3.7A load !

So, if you plan to use Isense with Vpower5 devices, you need to choose a 10A HSD to drive 3.5A... and this is true for VNQ5E160AK, VND5E160AJ etc

Other one I use is VN5050AJ, this one has a K factor of 1970 and so: work well up to 15A.

I had a quick look on Vpower7 serie, looks like they have the same K factor range and even lower Isense limitation!

Finally, I believe there is no real limitation on M1 Mos, that could be the reason driver burn when I load it with 8.3A, no related to main but to sense circuit.