ZHCS979F June 2012 – October 2020 TPS53318 , TPS53319
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 5-V LDO and VREG Start-Up
- 8.3.2 Adaptive On-Time D-CAP Control and Frequency Selection
- 8.3.3 Ramp Signal
- 8.3.4 Adaptive Zero Crossing
- 8.3.5 Output Discharge Control
- 8.3.6 Power-Good
- 8.3.7 Current Sense, Overcurrent, and Short Circuit Protection
- 8.3.8 Overvoltage and Undervoltage Protection
- 8.3.9 Redundant Overvoltage Protection (OVP)
- 8.3.10 UVLO Protection
- 8.3.11 Thermal Shutdown
- 8.3.12 Small Signal Model
- 8.3.13 External Component Selection Using All Ceramic Output Capacitors
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Applications
- 9.2.1
Application Using Bulk Output Capacitors, Redundant Overvoltage Protection Function (OVP) Disabled
- 9.2.1.1 Design Requirements
- 9.2.1.2
Detailed Design Procedure
- 9.2.1.2.1 Step One: Select Operation Mode and Soft-Start Time
- 9.2.1.2.2 Step Two: Select Switching Frequency
- 9.2.1.2.3 Step Three: Choose the Inductor
- 9.2.1.2.4 Step Four: Choose the Output Capacitor or Capacitors
- 9.2.1.2.5 Step Five: Determine the Value of R1 and R2
- 9.2.1.2.6 Step Six: Choose the Overcurrent Setting Resistor
- 9.2.1.3 Application Curves
- 9.2.2 Application Using Ceramic Output Capacitors, Redundant Overvoltage Protection Function (OVP) Enabled
- 9.2.1
Application Using Bulk Output Capacitors, Redundant Overvoltage Protection Function (OVP) Disabled
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
8.3.7 Current Sense, Overcurrent, and Short Circuit Protection
The TPS53318 and TPS53319 device offer cycle-by-cycle overcurrent limiting control. The inductor current is monitored during the OFF state and the controller maintains the OFF state during the period in that the inductor current is larger than the overcurrent trip level. In order to provide both good accuracy and cost effective solution, the TPS53319 device supports temperature compensated MOSFET RDS(on) sensing. The TRIP pin should be connected to GND through the trip voltage setting resistor, RTRIP. The TRIP terminal sources current (ITRIP) which is 10 μA typically at room temperature, and the trip level is set to the OCL trip voltage VTRIP as shown in Equation 2.
The inductor current is monitored by the LL pin. The GND pin is used as the positive current sensing node and the LL pin is used as the negative current sense node. The trip current, ITRIP has a 3000ppm/°C temperature slope to compensate the temperature dependency of the RDS(on). For each device, ITRIP is also adjusted based on the device-specific on-resistance measurement in production tests to eliminate the any OCP variation from device to device. Duty-cycle should not be over 45% in order to provide the most accurate OCP.
As the comparison is made during the OFF state, VTRIP sets the valley level of the inductor current. Thus, the load current at the overcurrent threshold, IOCP, can be calculated as shown in Equation 3.
where
- RTRIP is in Ω
In an overcurrent or short-circuit condition, the current to the load exceeds the current to the output capacitor thus the output voltage tends to decrease. Eventually, it crosses the undervoltage protection threshold and shuts down. After a hiccup delay (16 ms plus 0.7 ms soft-start period), the controller restarts. If the overcurrent condition remains, the procedure is repeated and the device enters hiccup mode.
where
- n = 8, 9, 10, or 11 depending on soft-start time selection
| SELECTED SOFT-START TIME (tSS)(ms) | HICCUP WAIT TIME (tHIC(wait))(ms) | HICCUP DELAY TIME (tHIC(delay))(ms) |
|---|---|---|
| 0.7 | 2.052 | 14.364 |
| 1.4 | 3.076 | 21.532 |
| 2.8 | 5.124 | 35.868 |
| 5.6 | 9.220 | 64.540 |
For the TPS53318 device, the OCP threshold is internally clamped to 10.5 A. The recommended RTRIP value for the TPS53318 device is less than 150 kΩ.