ZHCSL90 August 2020 TPS25980
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 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
- 8.4 Fault Response
- 8.5 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Application: Patient Monitoring System in Medical Applications
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Device Selection
- 9.2.2.2 Setting the Current Limit Threshold: RILIM Selection
- 9.2.2.3 Setting the Undervoltage Lockout Set Point
- 9.2.2.4 Choosing the Current Monitoring Resistor: RIMON
- 9.2.2.5 Setting the Output Voltage Ramp Time (TdVdt)
- 9.2.2.6 Setting the Load Handshake (LDSTRT) Delay
- 9.2.2.7 Setting the Transient Overcurrent Blanking Interval (tITIMER)
- 9.2.2.8 Setting the Auto-Retry Delay and Number of Retries
- 9.2.3 Application Curves
- 9.3 System Examples
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.3.2 Circuit Breaker
The TPS25980x responds to output overcurrent conditions by turning off the output after a user adjustable transient fault blanking interval. When the load current exceeds the programmed current limit threshold (ILIM set by the ILIM pin resistor RILIM), but lower than the fast-trip threshold (2.1 x ILIM), the device starts discharging the ITIMER pin capacitor using an internal pull-down current (IITIMER). If the load current drops below the current limit threshold before the ITIMER capacitor drops by ΔVITIMER, the circuit breaker action is not engaged and the ITIMER is reset by pulling it up to VINT internally. This allows short transient overcurrent pulses to pass through the device without tripping the circuit. If the overcurrent condition persists, the ITIMER capacitor continues to discharge and once it falls by ΔVITIMER, the circuit breaker action turns off the FET immediately. The following equation can be used to calculate the RILIM value for a desired current limit threshold.
Leaving the ILIM pin Open sets the current limit to zero and causes the FET to shut off as soon as any load current is detected. Shorting the ILIM pin to ground at any point during normal operation is detected as a fault and the part shuts down. The ILIM pin Short to GND fault detection circuit requires a minimum amount of load current (ICB) to flow through the device. This ensures robust eFuse behavior even under single point failure conditions. Refer to the Fault Response section for details on the device behavior after a fault.
Figure 8-3 Circuit Breaker ResponseThe duration for which load transients are allowed can be adjusted using an appropriate capacitor value from ITIMER pin to ground. The transient overcurrent blanking interval can be calculated using Equation 5.
Leave the ITIMER pin open to allow the part to break the circuit with the minimum possible delay.
| ITIMER Pin Connection | Timer Delay before Overcurrent response |
|---|---|
| OPEN | 0 s |
| Capacitor to ground | As per Equation 5 |
| Short to GND | ITIMER Pin Fault - Part Shuts Off |
1. Shorting the ITIMER pin to ground is detected as a fault and the part shuts down. This ensures robust eFuse behavior even in case of single point failure conditions. Refer to the Fault Response section for details on the device behavior after a fault.
2. Larger ITIMER capacitors take longer to charge during start-up and may lead to incorrect fault assertion if the ITIMER voltage is still below the pin short detection threshold after the device has reached steady state. To avoid this, it is recommended to limit the maximum ITIMER capacitor to the value suggested by the equation below.
Where
- tGHI is the time taken by the device to reach steady state
- tD,ON is the device turn-on delay
- Cdvdt is the dVdt capacitance
- Idvdt is the dVdt charging current
Once the part shuts down due to a Circuit Breaker fault, it can be configured to either stay latched off or restart automatically. Refer to the Fault Response section for details.