Dual Input RTC Supply Generator With Replica Power Path
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Solution Overview
Problem
Existing dual supply rail systems for real-time clocks (RTC) face challenges in achieving ultra-low power consumption from back-up sources and zero current consumption during main system supply presence, while also managing voltage variations across different power sources, leading to complex and inefficient circuit designs.
Innovation Solution
A dual input RTC supply generator with a replica power path and autonomous mode of operation, utilizing a latched supply comparator and buffer amplifier to ensure smooth power transfer and efficient voltage regulation, sourcing from the back-up supply when necessary and from the main system supply when the back-up is depleted or discharged, with a safety margin to prevent abrupt voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the RTC domain is powered directly from the back-up source, then the implementation is simple, but the back-up power source experiences constant discharge even when system supply is present
Solution Approach 1:
The patent introduces an intermediary power management circuit that sits between the back-up source and the RTC domain. This circuit includes detection circuits that monitor the presence of system supply and control switches that route power appropriately. The intermediary prevents direct connection of RTC to back-up source when system supply is available, thereby stopping unnecessary discharge while maintaining simple RTC implementation.
Solution Approach 2:
The patent employs feedback mechanisms through detection circuits that continuously monitor the status of system supply (presence/absence). Based on this feedback, the power management circuit automatically switches between power sources. When system supply is detected, the circuit redirects power flow to prevent back-up source discharge; when system supply is absent, it reconnects back-up source to RTC domain.
2Loss of energy
If a supply comparator is integrated to monitor and connect RTC power supply to the higher of the two rails, then power efficiency improves, but the RTC supply voltage level varies widely between 1.5V and 5.5V
Solution Approach 1:
The patent implements dynamic voltage regulation by introducing a voltage regulator that actively adjusts the RTC supply voltage based on the selected power source. Instead of directly connecting RTC to either back-up or system supply, the regulator dynamically adapts the voltage output to match RTC requirements regardless of input voltage variations. This dynamic adjustment resolves the wide voltage swing issue while maintaining the power efficiency benefits of source selection.
Solution Approach 2:
The patent changes the voltage parameter of the RTC supply by introducing regulation stages that transform the input voltage from either source into a stable, appropriate voltage level for RTC operation. The voltage regulator modifies the electrical parameter (voltage) to remain within acceptable ranges for RTC components, preventing the extreme voltage variations that would otherwise occur when switching between 1.5V back-up and 5.5V system supply.
3Reliability
If the back-up battery charger is kept permanently on to top up the back-up energy source, then the back-up source maintains charge, but the overall IC power consumption increases
Solution Approach 1:
The patent implements periodic charging action instead of continuous charging. The detection circuits monitor the charge status of the back-up source and activate the charger only when charging is needed (when back-up source voltage drops below a threshold). This periodic operation maintains adequate charge levels in the back-up source while avoiding continuous power consumption that would occur with permanent charger activation.
Data Source
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AI summary
Circuits and methods providing a electronic power supply applicable to any dual supply rail systems, which require a smooth and uninterrupted output supply and a replica power path and autonomous mode of operation from the system power supply are disclosed. In a preferred embodiment of the invention the power supply is applied to a real time clock. An Innovative Replica Power Path concept and circuit implementation ensures the smooth and uninterrupted transfer of power from one input source to the other. The circuit features a Latched Supply Comparator that guarantees the commutation to the Replica Power Path only happens after the voltage is settled. Zero power consumption from the back-up energy source is achieved in the presence of an alternative higher voltage source. The generated RTC supply voltage does not suffer from abrupt changes when the voltage level of the main system power source (battery or charger) is connected or disconnected. The invention allows for maximum utilization of the energy left in the main battery, thus extending the life of the lower capacity backup battery/super-cap.