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Power-On-Reset and Programmable Brown Out Detection Circuit with Very Low Steady State Current

IP.com Disclosure Number: IPCOM000242562D
Publication Date: 2015-Jul-24
Document File: 8 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Abstract

A Power-on-Reset (POR) cum Brown Out detection circuit is proposed that consumes very low steady state current. In addition, POR detection threshold is independent of the supply ramp rate by modification of the way of capacitor charging, the time taken by circuit to respond to consecutive brown-out has been reduced considerably.

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Power-On-Reset and Programmable Brown Out Detection Circuit with Very Low Steady State Current

Abstract

A Power-on-Reset (POR) cum Brown Out detection circuit is proposed that consumes very low steady state current. In addition, POR detection threshold is independent of the supply ramp rate by modification of the way of capacitor charging, the time taken by circuit to respond to consecutive brown-out has been reduced considerably.

Introduction

A POR circuit generates a system reset signal till power supply over which system is working reaches a safe value essential for the proper operation of the devices. The reset signal is very important especially for digital circuitry so that the digital devices always start in a known state. After the power supply crosses a threshold, reset is released and circuits begin functioning properly.

Systems also include brown-out detection circuitry, which asserts a reset signal to the system when the power supply falls below a threshold value required by the system to function properly. In other words, it acts as a measure to prevent the malfunction of the system in response to poor voltage supply that may occur due to poor voltage regulation.

These POR and brown detection circuits are always active in a system resulting in constant current consumption by them. Due to this constant current consumption, it has a direct implication over the life time of the system (devices). Apart from it, reduction in current consumption holds more importance for battery-powered devices.

Fig. 1 shows a conventional brown-out detector where the capacitor is charged from diode connected MOS. Due to this configuration, charging of the capacitor is slowed down when voltage across the capacitor reaches VDD-Vth (diode load), which reduces the capability of the circuit to respond to a successive brown-out event with similar brown-out threshold. In the proposed circuit, the capacitor is charged through a switch so that it does not affect the charging rate of the capacitor, thus ability of the circuit to respond to successive brown-out with same threshold is not impaired.

Figure 1. Brown-out detector

The proposed circuit consumes very low DC current while being active at the same time throughout the operation and possesses independence from supply ramp rate on POR assertion and de-assertion.  Due to PVT variations the detection thresholds are bound to vary and a usual way of circumventing this issue is to impart trimmability in the detection threshold. In the present architecture, a way to impart trimmability in the brown-out detection has been proposed. By modifying the way the capacitor is charged, time taken by the circuit to respond to successive brown-outs has been reduced considerably by a factor of 10.

Proposed Circuit Description

In the proposed circuit, supply level is detected by a resistor ladder circuit at the top which a PMOS P1 switch is connected that initially is in ON state. Initially, node A is at ground and as supply...