What Is a System Reset IC?
System Reset IC is a semiconductor device that monitors supply voltage and supplies a reset signal to the microcontroller.
When a voltage below the normal operating voltage range is applied to a microcontroller, the microcontroller is unable to operate according to the requirements of the control program. As a result, the internal data is destroyed and the electronic equipment cannot operate as originally expected, which may lead to a fatal situation.
The purpose of using System Reset ICs is to prevent such abnormal behavior of the microcontroller program.
Usage of System Reset ICs
The System Reset IC monitors the power supply voltage provided to the microcontroller and connects the output signal of the Reset IC to the microcontroller’s reset input signal terminal for use.
Microcontrollers are used in many devices, including information equipment such as PCs, smartphones, and tablet terminals; general home appliances such as refrigerators, air conditioners, and washing machines; AV equipment such as TVs, BD recorders, and audio equipment; automotive equipment such as cars and motorcycles; office equipment such as printers and scanners; and professional equipment such as measuring instruments and various test equipment. System Reset ICs are also used in many other types of equipment.
Principle of System Reset IC
Generally, an IC consists of three pins: a supply voltage pin (VDD), a GND pin, and a reset signal output pin (OUT).
The IC has a voltage detection function, and when the voltage input to VDD falls below a predetermined voltage, the microcontroller is reset to ensure stable System Reset IC operation.
How to Select a System Reset IC
System Reset ICs reset the microcontroller when the voltage of VDD is lower than the detection voltage, and release the reset when the voltage of VDD is higher than the detection voltage. It is important to select an IC that matches the voltage range of the microcontroller to be used.
Types of System Reset ICs
1. Output Type
There are two types of output types for the OUT pin of System Reset ICs: the Nch open drain type and the CMOS type. The Nch open drain type requires an external pull-up resistor on the OUT pin, while the CMOS type does not require an external pull-up resistor.
For the Nch open drain type, elements other than the microcontroller can be connected, but for the CMOC type, the IC and microcontroller must be connected one-to-one.
2. WDT (Watch Dog Timer) Type
In addition to products that simply detect a predetermined voltage and generate a system reset, there are also types that incorporate a WDT (Watch Dog Timer).
In addition to monitoring the voltage to generate a reset to the system, the built-in WDT also generates a reset to the microcontroller in case of abnormal operation of the microcontroller.
The WDT function is used by connecting the WDT signal output from the microcontroller to the reset IC. The WDT signal output from the microcontroller is a pulse signal with a constant frequency when the microcontroller is operating normally. However, if the microcontroller becomes unstable, the WDT signal will not have a constant frequency.
The reset IC monitors the frequency of the WDT signal and resets the microcontroller if the frequency is abnormal.
3. Type With Delay Timer
A type with a built-in delay timer is also available. This function releases the reset to the microcontroller after a set period of time has elapsed. The reset can be released stably even when excessive voltage fluctuations occur.