Trouble Shooting-Additional Voltage Detector (Reset IC) R3118K231C Solves The Problem

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

voltage detector ICs are generally used as supervisory circuits for power supply for uCons. However, uCons usually have a supervisory function of their own. The role of the voltage detector ICs is not only such a supervisory circuit. This example is such a case, an additional VD solves the problem.

NO.1   Background of the trouble

When an application wakes up by using a mechanical switch, an input node for the MOSFET driven by the mechanical switch should be "L" for a certain time. However, the voltage was unstable for a low percentage in mass production and found to be 100% secured at the level of "L". 

The circuit design change opportunity is limited, and area size is also limited. 

No.2   Customer's issue and condition confirmation

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

No.3    Troubleshooting Process 

According to the information from the customer, the part can be sorted out. Components selection conditions include：

1. Adding a voltage detector between the mechanical switch and the gate of the MOSFET

Supervisory voltage is the output voltage range of the mechanical switch. The voltage range is from 0V to 3V. Indefinite voltage range must be avoided, therefore a voltage detector with a SENSE pin is suitable.

2. Typical Characteristic of a voltage detector with SENSE pin.

The power supply and sense voltage are separated, therefore, when the input voltage for the SENSE pin is from "L" to "H", while the sense pin voltage is from 0V to the released voltage level, the output voltage keeps the "L" level. The figure shown right is the typical characteristic of the voltage detector, “ R3118”(2.7V threshold type).

3. Delay time setting

The adjustable delay time is suitable for the system. So, the released delay time should be adjustable by an external capacitor.

The device candidate is the R3118x.

4. Detector Threshold Voltage

Considering the distribution of the sense pin threshold, the detector threshold target is less than 2.5V and more than 2.0V.

5. Mount Area Size

The block diagram of the R3118xxxxC (CMOS output type)

The mount area size should be very small, Option is a tiny DFN(PLP)1212-6 package.

To reduce the number of components, the output type is CMOS type. ( pull-up resistance is not necessary.)

No.4   Conclusion

All things considered, the suitable device was the R3118K231C

For using this device, when the supervised voltage (SENSE pin voltage) is rising and reaches the released voltage, charging of the capacitor for delay time setting begins. When the capacitor is charged for a specific level, the output is released, and the voltage changes from "L" to "H". The capacitor charge is released internally after the output voltage is changed, but the output voltage is independent of the capacitor's condition once the condition is released.

The delay time capacitor is connected to the VDD pin via the delay time resistance as for conventional supervisory ICs,  In conventional type ICs, if some noise or condensation happens, the capacitor is discharged and output voltage may become "L".

But in the R3118 Series, once the SENSE pin voltage is released, unless otherwise, the SENSE pin itself detects "L", the output condition is independent of the delay time capacitor.

About NISSHINBO

New Japan Radio Co., Ltd. and Ricoh Electronic Devices Co., Ltd. of the Nisshinbo Group were integrated and started operation as Nisshinbo Micro Devices Inc. in January 2022. Nisshinbo integrated the strengths of both companies and refine "Connect Everything" technology, and, therefore, strives for further growth and development as an "Analog Solution Provider toward the realization of an ultra-smart society.