Trouble shooting-Additional Switch ICs solves the problem～

Checking circuit itself seemed to be OK, but a trouble is detected! As is often the case with such a trouble, an additional component is used. Here, the actual trouble shooting example is introduced. It might be useful to choose a device not only for trouble shooting but also just a simple component's selection.

This example is such kind of case.

Background
Customer's issue
Trouble shooting process

Case 3：Additional Switch ICs solves the problem

Switch ICs can cut off the power path and consumption current of the application can be suppressed. Simple on and off can be realized by using a MOSFET, but if you choose a switch IC, soft-start function and protection function can be expected.

Background of the trouble

The power line of the application is 3.3V. This line was directly connected to the device A and the device B. But the device A should start up later than device B and the input of device B should reach more than 1.5V when the device A start-up.

Customer's issue and condition confirmation

To solve the problem, some critical points must be considered.

Check points	Customer's issue and condition confirmation （Check points)
In other words, just realizing the timing lag is not enough. The power level should be more than a target and the device A starts up. Input voltage maximum is less than 5.5V. Considering some margin, until the input voltage of the device B reaches around 2V, the power line to the device A should be cut off.	Input voltage
The countermeasure circuit area size should be small. So without using a voltage detector, a load switch might be the best solution. ON/Off signal dedicated for the switch IC does not exist. It should be power up with power supply. The IC package should be as small as possible, WL-CSP type is prefereble. Soft-start should be built in the IC without external capacitor.	Mount area size
Peak current is extimated around 1A, considering this point, on resistance of the switch shuold be less than 100mohm.	Voltage drop considering by on resistance of the switch IC.

Trouble shoooting Process

According to the information from the customer, part can be sorted out.

Which type switch IC is the best?

So-called load switched are usually low voltage input is acceptable, in this case, it is not preferreble for considering the input voltage condition.
USB switch is one of candidates, but generally, the component size is relatively big. (Nisshinbo Micro Devices R5524K 1.8mm x 2.0mm)

Conclusion

We have an Ovp switch which can be used for this purpose. Part # is R5528Z

The R5528Z series have UVLO function. The released voltage is typically 2.05V.
The pacakge is WLCSP, 1.27mm x 1.27mm (0.64mm thickness). Current capability is 3A.
On resistance is 54mohm@5V.
Enable pin is "L" active. ENB pin is used for On and Off. In this case, if ENB pin is tied to GND, external control is unnecessary. Further, the debounce time is included after power on, so mis-operation by VIN ramp up variation can be avoided.