Contact Protection (Long/Short Pin Design) is a key protective design for hot-swappable modules.
We use the ADI LTC4210 as an example to demonstrate a typical single-channel 5V hot-swappable connector.
(1) Pin Design Logic
The PCB connector adopts a structure where Long Pins connect to power and Short Pins connect to control signals:
- Insertion: Long pins make contact with the backplane VIN first, followed by Short pins. The reverse occurs during extraction.
- Purpose: Prevent false triggering of the controller during incomplete mating and avoid abnormal currents caused by poor contact.
(2) ON Pin Detection Logic
The ON pin is connected to the Short pin via a 20kΩ resistor and to ground via a 10kΩ resistor, forming a voltage-level detection circuit:
- Unmated State: The Short pin is floating. The ON pin is at a low level (< 1.22V), causing the controller to pull GATE low and shut down Q1.
- Fully Mated State: The Short pin makes contact with the backplane GND. The ON pin is pulled high above the turn-on threshold (1.3V), triggering the controller to start the initial timing period.
(3) Initial Period Verification (Waveform Correlation)
In the power-up timing diagram, VON transitions first, followed by the slow rise of VTIMER. This accurately reflects the initial timing period:
- After confirming the mating is stable, the controller initiates the soft-start sequence, completely eliminating current anomalies caused by poor contact.
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