ZHCSNR7A March 2022 – August 2022 TPS55289
PRODUCTION DATA
- 1 特性
- 2 應(yīng)用
- 3 說明
- 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 EXTVCC Power Supply
- 7.3.3 Operation Mode Setting
- 7.3.4 Input Undervoltage Lockout
- 7.3.5 Enable and Programmable UVLO
- 7.3.6 Soft Start
- 7.3.7 Shutdown and Load Discharge
- 7.3.8 Switching Frequency
- 7.3.9 Switching Frequency Dithering
- 7.3.10 Inductor Current Limit
- 7.3.11 Internal Charge Path
- 7.3.12 Output Voltage Setting
- 7.3.13 Output Current Monitoring and Cable Voltage Droop Compensation
- 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 Programming
- 7.6
Register Maps
- 7.6.1 REF Register (Address = 0h, 1h)
- 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]
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
封裝選項
機械數(shù)據(jù) (封裝 | 引腳)
- RYQ|21
散熱焊盤機械數(shù)據(jù) (封裝 | 引腳)
- RYQ|21
訂購信息
8.2.2.3 Inductor Selection
Since the selection of the inductor affects steady state operation, transient behavior, and loop stability, the inductor is the most important component in power regulator design. There are three important inductor specifications: inductance, saturation current, and DC resistance.
The TPS55289 is designed to work with inductor values between 1 μH and 10 μH. The inductor selection is based on consideration of both buck and boost modes of operation.
For buck mode, the inductor selection is based on limiting the peak-to-peak current ripple to the maximum inductor current at the maximum input voltage. In CCM, Equation 9 shows the relationship between the inductance and the inductor ripple current.
where
- VIN(MAX) is the maximum input voltage.
- VOUT is the output voltage.
- ΔIL(P-P) is the peak to peak ripple current of the inductor.
- fSW is the switching frequency.
For a certain inductor, the inductor ripple current achieves maximum value when VOUT equals half of the maximum input voltage. Choosing higher inductance gets smaller inductor current ripple while smaller inductance gets larger inductor current ripple.
For boost mode, the inductor selection is based on limiting the peak-to-peak current ripple to the maximum inductor current at the maximum output voltage. In CCM, Equation 10 shows the relationship between the inductance and the inductor ripple current.
where
- VIN is the input voltage.
- VOUT(MAX) is the maximum output voltage.
- ΔIL(P-P) is the peak-to-peak ripple current of the inductor.
- fSW is the switching frequency.
For a certain inductor, the inductor ripple current achieves maximum value when VIN equals to the half of the maximum output voltage. Choosing higher inductance gets smaller inductor current ripple while smaller inductance gets larger inductor current ripple.
For this application example, a 4.7-μH inductor is selected, which produces approximate maximum inductor current ripple of 50% of the highest average inductor current in buck mode and 50% of the highest average inductor current in boost mode.
In buck mode, the inductor DC current equals to the output current. In boost mode, the inductor DC current can be calculated with Equation 11.
where
- VOUT is the output voltage.
- IOUT is the output current.
- VIN is the input voltage.
- η is the power conversion efficiency.
For a given maximum output current of the TPS55289, the maximum inductor DC current happens at the minimum input voltage and maximum output voltage. Set the inductor current limit of the TPS55289 higher than the calculated maximum inductor DC current to make sure the TPS55289 has the desired output current capability.
In boost mode, the inductor ripple current is calculated with Equation 12.
where
- ΔIL(P-P) is the inductor ripple current.
- L is the inductor value.
- fSW is the switching frequency.
- VOUT is the output voltage.
- VIN is the input voltage.
Therefore, the inductor peak current is calculated with Equation 13.
Normally, it is advisable to work with an inductor peak-to-peak current of less than 40% of the average inductor current for maximum output current. A smaller ripple from a larger valued inductor reduces the magnetic hysteresis losses in the inductor and EMI, but in the same way, load transient response time is increased. The selected inductor must have higher saturation current than the calculated peak current.
The conversion efficiency is dependent on the resistance of its current path. The switching loss associated with the switching MOSFETs, and the inductor core loss. Therefore, the overall efficiency is affected by the inductor DC resistance (DCR), equivalent series resistance (ESR) at the switching frequency, and the core loss. Table 8-2 lists recommended inductors for the TPS55289. In this application example, the Coilcraft inductor XAL7070-472 is selected for its small size, high saturation current, and small DCR.
| Part Number | L (μH) | DCR (Maximum) (mΩ) | Saturation Current/Heat Rating Current (A) | Size (L × W × H mm) | Vendor(1) |
|---|---|---|---|---|---|
| XAL7070-472ME | 4.7 | 14.3 | 15.2/10.5 | 7.5 × 7.2 × 7.0 | Coilcraft |
| VCHA085D-4R7MS6 | 4.7 | 15.6 | 16.0/8.8 | 8.7 × 8.2 × 5.2 | Cyntec |
| IHLP4040DZER4R7M01 | 4.7 | 16.5 | 17/9.5 | 10.2 × 10.2 × 4.0 | Vishay |