Texas Instruments manual Component Selection, TPS40051 Device Selection, Frequency of Operation

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SLUU161 – April, 2003

4 Component Selection

4.1TPS40051 Device Selection

The TPS4005x family of parts offers a range of output current configurations including source only (TPS40050), source/sink (TPS40051), or source/sink with VOUT prebias (TPS40053). In this converter the TPS40051 with source/sink capability is selected. This serves to maintain continuous inductor ripple current all the way to zero load to improve the small signal loop response by preventing the inductor current from transitioning to the discontinuous current mode.

The TPS4005x family is packaged in TI’s PWP PowerPAD thermally enhanced package which should be soldered to the PCB using standard solder flow techniques. The PowerPADtechnology uses a thermally conductive epoxy to attach the integrated circuit die to the leadframe die pad, which is exposed on the bottom of the completed package. The PWP PowerPAD package has a θ JC = 2° C/W which helps keep the junction temperature rise relatively low even with the power dissipation inherent in the onboard MOSFET drivers. This power loss is proportional to switching frequency, drive voltage, and the gate charge needed to enhance the N-channel MOSFETs. Effective heat removal allows the use of ultra-small packaging while maintaining high component reliability.

The technical brief, PowerPAD Thermally Enhanced Package[2] contains more information on the PowerPAD package.

4.2Frequency of Operation

The clock oscillator frequency for the TPS40051 is programmed with a single resistor from RT (pin 2) to signal ground. The following equation (1) from the datasheet allows selection of RT in kΩ for a given switching frequency in kHz.

 

 

 

1

 

 

W

 

(1)

RT + R2 + f

SW

17.82

10*6 * 23 (k

)

 

 

 

 

 

 

 

 

 

 

For 300-kHz operation, R2 is selected to be 165 kΩ.

For a particular operating frequency, the PWM ramp time must be programmed via the resistor RKFF connected to VIN. Also, the selection of RKFF programs the VIN voltage at which the circuit starts operation. This prevents the circuit from starting at low voltages, which can lead to current flow larger than desired. RKFF is programmed using equation (2).

RKFF + R6 + ￿VIN(min) * 3.5￿

￿58.14 RT ) 1340￿ (kW)

(2)

 

Where VIN(min) is the minimum startup input voltage, and RT is in kΩ . Note that internal tolerances have been incorporated into this equation, so the actual VIN(min) of the input voltage should be used. For an oscillator frequency of 300-kHz, the RKFF value of 71.5 kΩ is selected.

6TPS40051-Based Design Converts 12-V Bus to 1.8 V at 15 A (SLUP195)

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Contents User’s Guide EVM Important Notice Dynamic Warnings and Restrictions Features IntroductionSchematic TPS40051EVM-001 SLUP195 SchematicFrequency of Operation Component SelectionTPS40051 Device Selection + R2 + f 17.82 10 *6 * 23 kUvlo Circuitry Inductance ValueInput capacitor selection Output Capacitor Selection Mosfet selectionShort Circuit Protection Snubber Component SelectionCompensation Components Output Load Test SetupDC Input Source Oscilloscope Probe Test JacksEfficiency and Power Loss Test Results / Performance DataClosed Loop Performance EVM Assembly Drawing and PCB Layout Output Ripple and Transient ResponseTop Side Copper Internal Layer 2 Copper List of Materials TPS40051EVM-001 SLUP195 List of MaterialsReferences Important Notice

TPS40051 specifications

Texas Instruments TPS40051 is a highly integrated, synchronous step-down (buck) switching regulator designed to deliver power efficiently and effectively to various applications. This device is particularly well-suited for powering FPGAs, DSPs, microcontrollers, and other digital devices that require a stable voltage supply with high efficiency.

One of the main features of the TPS40051 is its ability to operate from a wide input voltage range of 4.5V to 17V. This flexibility makes it suitable for a variety of power sources, including battery-operated systems and traditional AC/DC power supplies. The output voltage can be adjusted from 0.8V to 85% of the input voltage, making it adaptable to different load requirements and application scenarios.

The TPS40051 employs a constant frequency, voltage mode control scheme, which results in improved transient response and stability. The device operates with a fixed switching frequency that can be set between 100kHz and 1MHz, allowing designers to optimize their designs for efficiency or minimize electromagnetic interference (EMI). The low RDS(on) of the integrated MOSFETs reduces conduction losses, contributing to the overall high efficiency of the solution, often exceeding 90%.

In terms of protection features, the TPS40051 includes overcurrent protection, thermal shutdown, and under-voltage lockout, which enhance the reliability of the system. These features allow the device to maintain safe operating conditions in various scenarios, protecting both the regulator and the load.

Another significant characteristic of the TPS40051 is its ability to operate in a Power Good mode. This feature provides feedback to the system regarding the status of the output voltage, allowing for better system monitoring and control. Additionally, it has an adjustable soft-start feature, which helps prevent inrush current during power-up, further protecting sensitive loads.

The TPS40051’s compact package options and its integration of features make it a flexible choice for designers looking to implement efficient power management solutions. Whether used in industrial, automotive, or consumer electronics applications, the TPS40051’s robust performance and adaptability make it an excellent choice for modern power supply designs.
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