Slave Charger Current Sensing Using BATFET Extraction
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Solution Overview
Problem
Traditional master-slave battery charging circuits face challenges with significant area usage and power loss due to the presence of front porch field-effect transistors (FPFETs) for input current sensing and reverse current blocking, especially in high-voltage domains, which complicates input current control and increases die area.
Innovation Solution
The proposed solution eliminates the FPFET in the slave charging circuit by using battery field-effect transistors (BATFETs) for input current feedback and reverse current blocking, allowing for area savings and improved layout flexibility, with a USBIN-to-VIN connection option, and implementing current-sensing circuits in a medium-voltage domain to reduce area and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If FPFETs are used for input current sensing and reverse current blocking in high-voltage domain, then reliable current control and reverse blocking are achieved, but die area increases significantly and power loss increases
Solution Approach 1:
The patent extracts the FPFET from the slave charging circuit and replaces it with BATFET-based current sensing. The FPFET was originally used for input current sensing and reverse current blocking, but its removal reduces die area while the BATFET maintains the necessary control functions through alternative circuitry configuration
Solution Approach 2:
The BATFET is made to serve multiple functions: it performs both input current sensing and reverse current blocking that were previously handled by the FPFET. This multi-functionality eliminates the need for separate high-voltage domain circuitry, reducing overall die area while maintaining reliability
2Reliability
If FPFETs are used for input current sensing and reverse current blocking, then reliable current control is achieved, but power loss increases
Solution Approach 1:
The FPFET is removed from the circuit, eliminating the power loss associated with its operation. The BATFET-based alternative reduces power consumption by operating in a different voltage domain and using more efficient current sensing methodology
Solution Approach 2:
The patent changes the operating voltage domain from high-voltage (FPFET) to medium-voltage (BATFET), which alters the electrical parameters and reduces power loss. This parameter change allows the same functional requirements to be met with lower energy dissipation
3Measurement precision
If high-voltage domain circuitry is used for current sensing, then accurate sensing is achieved, but die area and power loss increase
Solution Approach 1:
The patent changes the voltage domain parameter from high-voltage to medium-voltage for current sensing operations. This parameter change allows accurate current measurement to be achieved with BATFET-based circuitry that occupies less die area and consumes less power compared to traditional high-voltage FPFET circuitry
Data Source
AI summary
Certain aspects of the present disclosure generally relate to reducing the size of parallel charging circuits for charging a battery in a portable device, while still effectively providing input current sensing and reverse current blocking capabilities. One example battery charging circuit generally includes: (1) a first charging circuit comprising a first charging output connectable to a battery and a first converter to provide power to the first charging output; and (2) a second charging circuit comprising a second charging output connectable to the battery, a second converter to provide power to the second charging output, a first transistor coupled between an output of the second converter and the second charging output, and a current-sensing circuit coupled to the output of the second converter to sense a current through the first transistor.