Texas Instruments TPS40051 manual Short Circuit Protection, Snubber Component Selection

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SLUU161 – April, 2003

4.8Short Circuit Protection

The TPS40051 implements short circuit protection by comparing the voltage across the topside MOSFET while it is ON to a voltage developed across RLIM due to an internal current source of 10 µ A inside pin 16. Both of these voltages are negative with respect to VIN. From the datasheet equation, RLIM is defined as:

RLIM

+ R9 +

IOC RDS(on) (max)

+

VOS

 

+ (W)

(10)

1.12 ISINK

ISINK

 

 

 

 

 

 

where

•

•

IOC is the overcurrent set point equal to the DC output current plus one-half the inductor ripple current

VOS is the overcurrent comparator offset, and Isink is the current into ILIM (pin 16).

Using worst case tolerances the value of RLIM should be maximized to ensure that the converter can deliver full rated current under all conditions. In a worst case condition, RLIM=R9 and

R

LIM

+

 

(15 A ) 1.5 A)

(7.9 mW

1.45)

)

* 30 mV

+ 16.0 kW

(11)

1.12

8.65 mA

 

 

 

 

 

8.65 mA

 

 

The standard value of 16.2 kΩ was selected. This ensures that we can deliver a minimum of 15 A before current limit is activated. There is also a small capacitor, C7, placed in parallel with R9 to filter the signal.

4.9Snubber Component Selection

Initially, the junction of Q1, Q2, and L1 was ringing at a frequency near 100 MHz with a peak voltage near 30 V. This was due to the extremely fast switching speed of the MOSFETs and the lack of any cross–conduction. C13 was added to shunt the high-frequency ringing to ground and the peak voltage is now below 25 V.

4.10 Compensation Components

The TPS40051 uses voltage mode control with feed-forward in conjunction with a high-frequency error amplifier to implement closed loop control. The power circuit L-C double pole corner frequency fC occurs at 3.8 kHz, and the output capacitor ESR zero is located at approximately 38 kHz. The feedback compensation network is implemented to provide two zeroes and three poles. The first pole is placed at the origin to improve DC regulation.

The first zero is placed at 2.8 kHz, just below the L-C corner frequency.

fZ1 +

1

2p R5 C5

The second zero is selected to be coincident with the L-C corner frequency of 3.8 kHz,

fZ2

+

 

1

2p

(R7 ) R8) C6

 

 

The second pole is placed near the ESR zero frequency at 37 kHz.

fP1 + 2p R5 1 ￿C4 C5￿ C4)C5

and the third pole is placed at 150 kHz, which is one-half the switching frequency.

fP2 +

1

2p R8 C6

(12)

(13)

(14)

(15)

TPS40051-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 Introduction FeaturesTPS40051EVM-001 SLUP195 Schematic SchematicTPS40051 Device Selection Component SelectionFrequency of Operation + R2 + f 17.82 10 *6 * 23 kUvlo Circuitry Inductance ValueInput capacitor selection Mosfet selection Output Capacitor SelectionShort Circuit Protection Snubber Component SelectionCompensation Components DC Input Source Test SetupOutput Load Oscilloscope Probe Test JacksEfficiency and Power Loss Test Results / Performance DataClosed Loop Performance Output Ripple and Transient Response EVM Assembly Drawing and PCB LayoutTop Side Copper Internal Layer 2 Copper TPS40051EVM-001 SLUP195 List of Materials 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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