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Reset timer IC for mobile devices

Ricoh Electronic Devices has launched the R3201, an IC for portable devices with a built-in battery and the possibility to reset the software to resume normal operation.

The IC also provides a so called “Shipping Mode” to reduce current consumption when the device is stored in a warehouse or during shipment. Devices with internal or pre-installed batteries that are stored for too long in standby mode will drain the batteries and may be completely exhausted before being delivered to the customer for initial use. Target applications include mobile phones, tablets, cameras, medical devices, wearables, portable game consoles, and music players.

Due to the complex level of functions available on portable devices, there is a possibility that it may lock up due to a software malfunction. In such case, it is necessary to initiate a reset cycle to return to normal operation. It can be done in several ways such as pressing a dedicated reset switch or by holding two available buttons. In the worst case the batteries has to be removed for a short period.

The R3201 can provide a reset cycle to the application processor that is long enough to reset it properly. It has two independent reset request inputs (RST0, RST1) to connect a single reset switch or by using two available device buttons. In order to prevent an accidental reset cycle, these switches need to be activated and held for a certain period. One is able to select from an optional 8 / 10 / 12 or 16 seconds delay time, which is internally fixed by product version. Once the reset cycle is triggered, it will provide an actual reset period of 0.4 seconds.

Both RST0 and RST1 input have an incorporated debounce circuit with a delay time of 10 msec.

The main advantage of the R3201 compared to a conventional reset timer IC is its ability to minimise current consumption of the device in the shipping mode. When a device is set into the standby mode, some components like the reset timer remain in On-mode whilst all other ICs are set to the Off mode. However, even in Off-mode there is still an amount of leakage current caused by these ICs.

The application processor is able to send a short clock pulse burst to the “Off” input pin and the R3201 will switch to the shipping mode after 15 seconds. As a result, the SRO output will control an external MOSFET disconnecting the battery line from the circuit, in this way the Off-mode leakage current is avoided and prolongs battery life significantly. The output even has a specific slew rate in order to switch the power supply smoothly. The second nSRO output is used for example to control an LDO or DC/DC Converter to the standby mode.

The shipping mode is released by activating the Power-On button for more than 2 seconds or by applying a power adapter to the device, detected by the TAIN input. This input has a breakdown voltage of 12 V but can be extended to 30 V by using a series resistor of 100 kΩ. In the shipping mode all redundant circuits are isolated from the power supply and the remaining current consumption ofthe R3201 is only 0.35µA.

The R3201 has two (N-channel open drain) discharge outputs available called DCHG1 and DSCHG2. The goal is to discharge output capacitors to ground during the reset cycle ensuring that the power lines are completely de-energized.

Neil Tyler

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