LCD Gate Driver Power Sequencing to Prevent VGH/VGL Latch-Up
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Solution Overview
Problem
Conventional LCD gate drivers face issues with voltage sequence errors, leading to latch-up and potential damage due to transient currents when gate high voltage (VGH) and gate low voltage (VGL) signals are not properly sequenced, often requiring external components or complex timing controllers to ensure VGL enters before VGH.
Innovation Solution
A power sequence control circuit with a voltage pull-up stage, voltage pull-down stage, and current limit switching unit is integrated into the gate driver, utilizing MOS transistors and diodes to control the sequence of VGH and VGL signals, ensuring VGL enters the gate driver earlier than VGH without external resistors or capacitors, thus preventing latch-up and reducing production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external components (resistors and capacitors) are used to control voltage sequence, then the latch-up problem is prevented, but production cost increases and device complexity increases
Solution Approach 1:
The patent merges the voltage sequence control function with the existing gate driver circuit by integrating the control circuit 124 into the gate driver chip. The control circuit uses the existing power block outputs VGHp and VGLp directly, eliminating the need for separate external resistors and capacitors. This integration combines multiple functions (power sequencing, transient current prevention, and latch-up avoidance) into a single unified circuit design, thereby reducing overall device complexity while maintaining reliability.
Solution Approach 2:
The patent extracts the voltage sequence control functionality from the external component level and relocates it to the internal circuit level. By taking out the control logic from external resistors/capacitors and embedding it in the gate driver's control circuit 124, the design eliminates external components while preserving the protective function against latch-up and transient currents.
2Reliability
If timing controller controls power sequence, then voltage sequence error is prevented, but production cost increases
Solution Approach 1:
The patent combines the power sequence control function with the gate driver circuit itself, eliminating the need for a separate timing controller to manage power sequencing. The control circuit 124 within the gate driver directly manages the timing and sequence of VGH and VGL voltages, merging what would otherwise be separate control functions into a single integrated unit, thereby reducing production costs.
Solution Approach 2:
The patent extracts the power sequence control responsibility from the timing controller and relocates it to the gate driver's internal control circuit. This extraction reduces the timing controller's complexity and eliminates the need for additional external control signals, simplifying the overall system architecture and reducing manufacturing costs.
3Speed
If VGH enters gate driver before VGL, then power delivery is faster, but transient current occurs causing damage
Solution Approach 1:
The patent applies preliminary action by having the control circuit 124 pre-establish the correct voltage sequencing before power is fully applied. The circuit ensures VGL is properly established before VGH is fully applied, preventing transient current damage while maintaining fast power delivery. The control logic proactively manages the timing relationship between the two voltage inputs.
Solution Approach 2:
The control circuit 124 acts as an intermediary between the power block and the gate driver's voltage inputs. It mediates the timing relationship between VGHp and VGLp, ensuring proper sequence while allowing fast power delivery. The control circuit buffers and coordinates the voltage applications, preventing direct transient current coupling while maintaining speed.
4Reliability
If external components are used for sequence control, then IC damage is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent merges the IC protection function with the gate driver circuit by integrating the control circuit 124 directly into the gate driver chip. The control circuit combines power sequencing, transient current prevention, and latch-up avoidance into a single integrated design, eliminating external protective components and reducing overall device complexity while maintaining IC protection.
Solution Approach 2:
The patent extracts the protection functionality from external components and relocates it to the internal control circuit of the gate driver. By taking out the protective control logic from external circuitry and embedding it in the gate driver's integrated circuit, the design eliminates external components while preserving IC protection capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively integrates into the IC, ensuring proper voltage sequencing without external components, reducing production costs and preventing damage from transient currents, while maintaining efficient discharge and operation within a wide voltage range.
Implementation Method 1
The voltage pull-down stage pulls down a control voltage corresponding to the node
Implementation Method 2
the current limit switching unit conducts to transmit the input positive voltage as the output positive voltage
Implementation Method 3
utilizing MOS transistors and diodes to control the sequence of VGH and VGL signals
Data Source
AI summary
A power sequence control circuit receives an input positive voltage and an input negative voltage. The control circuit includes a pull-up stage, having a first terminal receiving the input positive voltage, a second terminal coupled to a node, and a control terminal receiving feedback of an output positive voltage. A pull-down stage has a first terminal coupled to the node and a second terminal coupled to an output negative voltage. A current-limit switching unit has a first terminal receiving the input positive voltage, a second terminal outputting the output positive voltage, and a control terminal coupled to the node. When the output negative voltage decreases, and if the pull-down stage decreases a control voltage at the node and the control voltage is less than a threshold value, the current-limit switching unit is conducted to transmit the input positive voltage as the output positive voltage.