This post explains for the voltage detector.

The Part Number is KIA7042AP.

The function of this semiconductor is 4.2V, Voltage detector.

Manufacturer: KEC

Preview images :

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Description

Function of KIA7042AP is accurately resetting the system after detecting voltage at the time of switching power on and instantaneous power off in various CPU systems and other logic systems.

A voltage detector is an electronic device or circuit designed to detect the presence or absence of voltage in an electrical circuit or at a specific point within that circuit. Voltage detectors are commonly used in various applications to ensure safety, troubleshoot electrical systems, or automate processes. They serve as a simple and effective means of checking whether voltage is present without the need for more complex measurement instruments like multimeters.

Features

1. Current Consumption is Low. ICCL=300 A Typ. ICCH=30 A Typ.

2. Resetting Output Minimum Guarantee Voltage is Low 0.8V Typ.

3. Hysteresis Voltage is Provided. 50mV Typ […]

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Applications:

1. As Control Circuit of Battery-Backed Memory.

2. As Measure Against Erroneous Operations at Power ON-OFF.

3. As Measure Against System Runaway at Instantaneous Break of Power Supply etc.

4. As Resetting Function for the CPU-Mounted Equipment, such as Personal Computers, Printers, VTRs and so forth

KIA7042AP PDF Datasheet