PMOS Load Switch Gate Control for Fast Soft Start
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Solution Overview
Problem
Conventional switching devices face challenges in preventing abrupt current flow and ensuring quick activation, which can lead to breakdowns in connected modules due to sudden voltage application.
Innovation Solution
The proposed switching device incorporates a load switch IC with a pre-discharge circuit and a slew rate control circuit, which gradually lower the voltage at the gate of a PMOS transistor, preventing abrupt current flow and enabling rapid activation by controlling the output-on time and current independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the voltage at the gate of the PMOS transistor is lowered quickly to activate the switching device, then the activation speed is improved, but abrupt current flow occurs causing breakdown in connected modules
Solution Approach 1:
The pre-discharge circuit lowers the voltage at the gate of the PMOS transistor before the main switching action occurs. This preliminary voltage reduction prepares the gate for safe switching by preventing excessive voltage that would cause abrupt current flow, while still enabling quick activation when the switching signal is applied.
Solution Approach 2:
The pre-discharge circuit acts as an intermediary between the voltage source and the gate of the PMOS transistor. It mediates the voltage transition by gradually discharging the gate voltage through a controlled path, preventing direct application of full voltage that would cause harmful current spikes.
2Reliability
If the voltage at the gate is lowered gradually to prevent abrupt current flow, then the safety is improved, but the activation time increases
Solution Approach 1:
The pre-discharge circuit performs a preliminary voltage reduction that is safe and controlled, preparing the gate for subsequent quick switching. This preliminary action ensures safety by preventing voltage spikes, while the overall activation time remains short because the main switching action follows immediately after the pre-discharge phase.
Data Source
AI summary
A gate of the first p-type MOS transistor and the first and second control circuits are electrically coupled to a first node. The first control circuit lowers a voltage or the first node between a first time and a second time at which the first p-type MOS transistor is off. The second control circuit lowers the voltage of the first node between a third time and a fourth time at which the first p-type MOS transistor is on. The second time is later than the first time. The fourth time is later than the second and third times. The first p-type MOS transistor is turned on during a first period. A voltage decrease amount of the first node per unit time in the first control circuit is greater than that in the second control circuit.