Circuit Breaker Delay Turn-Off (tCBDELAY) is a critical layered fault protection mechanism for hot-swappable controllers. It serves two core purposes:
- Filter Transient Overcurrents: Prevent false shutdowns caused by load transient spikes (e.g., capacitor charging, motor startup), ensuring the system operates continuously during normal transients.
- Protect Power Devices: In the event of a sustained overcurrent/short circuit, shut down the MOSFET after the delay to prevent it from overheating and burning out while operating in the constant current region.
We use the ADI LTC4210 as an example to demonstrate a typical single-channel 5V hot-swappable connector.
Circuit Breaker Delay is Determined by TIMER Capacitor Charging:The controller uses an internal 60μA current source to charge the external capacitor CTIMER.When the capacitor voltage charges from 0V to the COMP2 threshold of 1.3V, the circuit breaker shutdown is triggered.
From the Capacitor Charging Formula:
Rearranged for Delay Time:tCBDELAY = 1.3V × 0.22μF / 60μA ≈ 4.7ms
Fault Triggering:If the overcurrent state persists for more than 4.7ms and the TIMER voltage reaches 1.3V (COMP2 threshold), the controller immediately pulls GATE low to shut down Q1.
Auto-Retry (LTC4210-3 Feature):After a fault shutdown, the TIMER capacitor cools down and restarts automatically.
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