Other Parts Discussed in Thread: CSD19535KTT
Hi there,
I am experiencing some strange performance from the eFuse TPS2490 when used in my circuit. The problem might come from an incorrect choice of components, or from the harsh operating environment.
I am working with a design using 2x independent TPS2490 controlling 2 x independent CSD19535KTT transistors. The loads connected on the outputs draw maximum 10 A each. There are 22 uF capacitors connected at the output nodes as well. The circuit includes the soft start circuitry. The enable signal is controlled from a logic circuit that does not depend on the VCC value (it is connected to a logic power supply). The operation of the circuit is as follows:
The TPS2490 is given the enable signal to operate. EN voltage then exceeds the threshold of 1,35 V and establishes at a voltage of 1,5 V. The bypass transistor then goes ON, with little VDS and only 100 mA current upon startup. Later on, the load is modified (Load Activated timing below), increasing the current going through the switch. This increase in current can be soft (some seconds). In both conditions, after a certain value of current (3 Amps per efuse), the TPS2490 shows the following curves.
Here, prior to the first changes in the signals (labeled Load Activated), the load draws only 100 mA, and the VDS of the bypass transistor is very low (there is ~50 V on the drain of the device). When the load is changed, there can be sometimes a small peak of current (much less than the limiting value), and the TPS keeps starting up repeatedly, putting a lot of stress on the transistor. If the circuit is kept under this condition, the case temperature can easily reach 100°C. This continuous start-up condition does not stop at any point, I need to interrupt the power supply prior to any damage on the transistors. I have tried removing the soft start circuitry as well, with no positive effect. The scope screenshot below:
It is important to clarify that the load generates an important amount of EMI that can eventually affect the eFuses. This EMI is related to the amount of current drawn by the load: The higher the current, the bigger the EMI.
When observing the Gate voltage, it has the same shape as the OUT(Source). In my opinion, it is either a bad choice of the components of the circuit, or the EMI affecting the gate driver forcing it to restart. I do not see how the gate/source signals can change if the Limit pin is not being charged.
I attach the Calculator file for this circuit. Any help is highly appreciated.
