Hello,
I am using current sensing IC INA300-Q1 for overcurrent sensing for 2A limit. if I checked this IC independently, it works, it goes low after 2A current sensed. i have added switch and control circuit before load. that time the alert signal does not go low, it remains on, please look into this issue and suggest any solution. I have attached schematic herewith.
Hello Priya,
We tested the setup you referenced (tidubk1b) with a few modifications in the test conditions. In our setup, we used 150 ohm Limit resistors to set the threshold current to 2A for a 0.003 ohm shunt. Our common mode is set at 6V. In this instance our ALERT LED dimmed when the device was operated in transparent mode (Latch pin shorted to ground). This corresponds to the ALERT toggling between on and off with a large duty cycle (ALERT typically high, see Figure 1). You could alternatively observe this through a DC measurement with your multimeter, which should indicate that the ALERT is a few hundred mV lower than 3.3V. To illustrate why this occurs, we first will simplify the bidirectional switch with protection to a simple switch symbol (figure 2). While the current is below the over-current condition, the device passes the current (figure 3). After the threshold is crossed, the ALERT pin transitions to low after a small delay and thereupon the gate closes after some additional delay (figure 4). At this point only a trickle of leakage current passes through to the sense pins. Since the current level is way below the threshold, the alert re-asserts high (figure 5). Then the cycle repeats itself until the upstream source provides a smaller load. Figure 6 illustrates the signal behavior with ISense included.
Figure 1: Measured Alert Signal
Figure 2: Bidirectional Switch Simplification
Figure 3: Bidirectional Switch Operation for Current below threshold
Figure 4: Bidirectional Switch Operation when limit threshold exceeded
Figure 5: Bidirectional Switch Operation after INA300 cut-off from Load
Figure 6. Signal Transient Response
The proposed fix for this circuit would be to implement a circuit like what is shown in the following schematic, with the INA381 swapped out with an INA300. (Example Circuit). The following circuit essentially allows the off time to last considerably longer before automatically allowing the load to pass through the switch. This circuit accomplishes this by ANDing the ALERT signal with an output signal from an LM555 timer. The CVOLT capacitor determines the duration the fuse switch is off. You can increase this value to increase the time off period.
Hello Priya,
1 - I am not sure what your query is here. If the ALERT is asserted and BSS138 MOSFET is turned on, I suspect that alot of current will pass through its relatively small RDSon if you removed the 10kohm resistor that should be in series with it. If you did not remove it and it is still getting hot, there may be another issue. A heat sink will probably help, but that will not fix the root issue. You are talking about the MOSFET pictured below right?
2. We only have a few other current sensing devices with comparators included in them. Those with a programmable delay include the INA203, INA204, INA205, INA206, INA207, and INA208. Otherwise did you ever get a chance to try this circuit we recommended above?
hello Simmons,
I am talking about MOSFET Q2, which was heated very fast, when we will pass 2A current in this circuit.
I have attached INA300-Q1 schematic herewith, in that i made some changes like, i want to keep this circuit in transparent mode so i connected latch pin to ground as discussed with you. but with this corrections alert signal goes low, once 2A overcurrent detected. but that time MOSFET Q2 is heated very fast.
i want to keep circuit in transparent mode because i need auto-recovery function after overcurrent is removed.. in latch mode, the alert remains low, if overcurrent condition is removed.
