ZHCSL91B October 2020 – March 2022 TPS25947
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 Input Reverse Polarity Protection
- 8.3.2 Undervoltage Lockout (UVLO and UVP)
- 8.3.3 Overvoltage Lockout (OVLO)
- 8.3.4 Overvoltage Clamp (OVC)
- 8.3.5 Inrush Current, Overcurrent, and Short Circuit Protection
- 8.3.6 Analog Load Current Monitor
- 8.3.7 Reverse Current Protection
- 8.3.8 Overtemperature Protection (OTP)
- 8.3.9 Fault Response and Indication (FLT)
- 8.3.10 Auxiliary Channel Control (AUXOFF)
- 8.3.11 Power Good Indication (PG)
- 8.4 Device Functional Modes
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.5.2 Circuit-Breaker
The TPS259474x (Circuit-Breaker) variants respond to output overcurrent conditions by turning off the output after a user adjustable transient fault blanking interval. When the load current exceeds the set overcurrent threshold (ILIM) set by the ILM pin resistor (RILM), but stays lower than the fast-trip threshold (2 x ILIM), the device starts discharging the ITIMER pin capacitor using an internal 1.8-μA pull-down current. If the load current drops below ILIM before the ITIMER pin capacitor (CITIMER) discharges by ΔVITIMER, the ITIMER is reset by pulling it up to VINT internally and the circuit breaker action is not engaged. This allows short load transient pulses to pass through the device without tripping the circuit. If the overcurrent condition persists, the CITIMER continues to discharge and after it discharges by ΔVITIMER, the circuit breaker action turns off the HFET immediately. At the same time, the CITIMER is charged up to VINT again so that it is at its default state before the next overcurrent event. This ensures the full blanking timer interval is provided for every overcurrent event. Equation 5 can be used to calculate the RILM value for a overcurrent threshold.
Leaving the ILM pin open sets the current limit to nearly zero and results in the part breaking the circuit with the slightest amount of loading at the output.
Shorting the ILM pin to ground at any point during normal operation is detected as a fault and the part shuts down. There is a minimum current (IFLT) which the part allows in this condition before the pin short condition is detected.
The duration for which transients are allowed can be adjusted using an appropriate capacitor value from ITIMER pin to ground. The CITIMER value needed to set the desired transient overcurrent blanking interval can be calculated using Equation 6.
Figure 8-9 TPS259474x Overcurrent Response - Leave the ITIMER pin open to allow the part to break the circuit with the minimum possible delay.
- Shorting the ITIMER pin to ground results in minimum overcurrent response delay (similar to ITIMER pin open condition), but increases the device current consumption. This is not a recommended mode of operation.
- Increasing the ITIMER cap value extends the overcurrent blanking interval, but it also extends the time needed for the ITIMER cap to recharge up to VINT. If the next overcurrent event occurs before the ITIMER cap is recharged fully, it takes lesser time to discharge to the ITIMER expiry threshold, thereby providing a shorter blanking interval than intended.
After the part shuts down due to a Circuit Breaker fault, it can either stay latched off (TPS259474L variant) or restart automatically after a fixed delay (TPS259474A variant).