ZHCSKY4B November 2018 – December 2020 TPS55288
PRODUCTION DATA
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 VCC Power Supply
- 7.3.2 Operation Mode Setting
- 7.3.3 Input Undervoltage Lockout
- 7.3.4 Enable and Programmable UVLO
- 7.3.5 Soft Start
- 7.3.6 Shutdown and Load Discharge
- 7.3.7 Switching Frequency
- 7.3.8 Switching Frequency Dithering
- 7.3.9 Inductor Current Limit
- 7.3.10 Internal Charge Path
- 7.3.11 Output Voltage Setting
- 7.3.12 Output Current Monitoring and Cable Voltage Droop Compensation
- 7.3.13 Integrated Gate Drivers
- 7.3.14 Output Current Limit
- 7.3.15 Overvoltage Protection
- 7.3.16 Output Short Circuit Protection
- 7.3.17 Thermal Shutdown
- 7.4 Device Functional Modes
- 7.5 I2C Serial Interface
- 7.6
Register Maps
- 7.6.1 REF Register (Address = 0h, 1h) [reset = 11010010h, 00000000h]
- 7.6.2 IOUT_LIMIT Register (Address = 2h) [reset = 11100100h]
- 7.6.3 VOUT_SR Register (Address = 3h) [reset = 00000001h]
- 7.6.4 VOUT_FS Register (Address = 4h) [reset = 00000011h]
- 7.6.5 CDC Register (Address = 5h) [reset = 11100000h]
- 7.6.6 MODE Register (Address = 6h) [reset = 00100000h]
- 7.6.7 STATUS Register (Address = 7h) [reset = 00000011h]
- 7.6.8 Register Summary
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
7.3.12 Output Current Monitoring and Cable Voltage Droop Compensation
The TPS55288 outputs a voltage at the CDC pin proportional to the sensed voltage across a output current sensing resistor between the ISP pin and the ISN pin. Equation 7 shows the exact voltage at the CDC pin related to the sensed output current.
To compensate the voltage droop across a cable from the output of the USB port to its powered device, the TPS55288 can lift its output voltage in proportion to the load current. There are two methods in the TPS55288 to implement the compensation: by setting internal register 05h or by placing a resistor between the CDC pin and AGND pin.
When using internal output voltage feedback, it is recommended to use the internal compensation setting. When using an external resistor divider at the FB/INT pin to set the output voltage, it is recommended to use the external compensation setting by placing a resistor at the CDC pin.
By default, the internal cable voltage droop compensation function is enabled with 0 V added to the output voltage. Write the value into the bit CDC [2:0] in register 05h to get the desired voltage compensation.
When using external output voltage feedback, external compensation is better than the internal register for its high accuracy. The output voltage rises in proportion to the current sourcing from the CDC pin through the resistor at the CDC pin. It is recommended to use 100-kΩ resistance for the up resistor of the feedback resistor divider. Equation 8 shows the output voltage rise related to the sensed output current, the resistance at the CDC pin, and the up resistor of the output voltage feedback resistor divider.
where
- RFB_UP is the up resistor of the resistor divider between the output and the FB/INT pin
- RCDC is the resistor at the CDC pin
When RFB_UP is 100 kΩ, the output voltage rise versus the sensed output current and the resistor at the CDC pin is shown in Figure 7-6.
Figure 7-6 Output Voltage Rise vs Output Current