Ultra-Low Power Button Reset with GreenPAK

Introduction

This solution is very important for use in widely distributed digital devices such as smartwatches, smartphones, wireless headphones, tablet PCs, and other small devices that have high requirements for low power consumption and battery life.

The operation of the design is founded on the low-frequency watchdog pulse generator, the button push detector, and a set of logic for generating a reset pulse with or without delay.

The GreenPAK has enough macrocells and configurable PINs to adapt the design to the specific needs of users.

We created this project in Go Configure™ Software Hub | Renesas. The complete design file can be found at Ultra-low Power Button Reset with GreenPAK.gp. More application notes here.

Operation of the Ultra-low power Button Reset

In this article three GreenPAK devices were selected to check and evaluate the level of current consumption: SLG46140,SLG46811, and SLG46855.

Since the main task of the device under development is a constant check of the condition of the external button (on/off) with minimal current consumption, for clock delay blocks and counter blocks in the design a low-frequency oscillator is used.

From the low-frequency watchdog pulse generator (WD) the low-frequency pulses, through the 1M resistor, are applied to the “Button” input PIN. Also, the S1 button is connected to the “Button” PIN, which when pressed pulls down it to the GND. This allows to determine the condition of the button (on/off) using a frequency detector and generate a reset pulse to the RESET output PIN with delay time or without it (see Waveform 1. The main design functionality and the Figures 1–6).

Channel 1 (yellow/top line) –Button

Channel 2 (light blue/2nd line) –RES_DLY ON/OFF

Channel 3 (magenta/3rd line) –RESET

Figures 1, 3, 5 and Figures 2, 4, 6 show the circuits of the proposed application and the design block diagrams for each selected device.

Table 1. shows the current consumption values for the SLG46140 at different values of the period of the frequency of the low-frequency watchdog generator to determine its optimal settings.

As can be seen from the data given in Table 1, the lowest current consumption is at Tw/s = 200 ms, so the rest of the data will be taken at Tw/s = 200 ms. See the data in Table 2–4.

Conclusion

The current consumption values shown in Tables 1–4 are the average values of more than 200 measurements for each value, measured with a Digital Multimeter SIGLENT SDM3065X.

As we can see from the data given in Tables 2–4, the current consumption for SLG46140, SLG46811, and SLG46855 is close to 500nA but the lowest current consumption measured for SLG46855 is less than 500nA, so it can be considered that the goal has been achieved.

In addition, there are still many unused resources that can be additionally used for the needs of the users.