Hello, my name is Katelyn Wiggenhorn, and I am a systems engineer at Texas Instruments in our bug converters and controllers team. Today, I will be talking about selecting wide input DC/DC converters for commercial vehicle telematics. Shown on the middle of this slide, there is a block diagram for an automotive telematic system. For this video, we will focus on the front-end power supply. 

In a commercial vehicle, the supply is powered by a 24-volt battery. And this off-battery converter supplies a second stage point-of-load converter, or a PMIC, along with the analog circuitry. Typically, the off-battery converter has an output rail of four to five volts with a one amp load and a five amp load peak for a 4G GPS signal. The five key requirements of this off-battery power supply are, a wide input range to cover cold crank and low dump transient conditions, high ambient temperature as the PCP board will be sitting inside a metallic box, a small solution size, low EMI, and a long service life. 

The typical supply voltage for a telematic system in a commercial vehicle will be a 24-volt battery. However, the battery voltage can fluctuate over a wide range of voltages, resulting from cold crank and low dump conditions. As detailed in the ISO, 16750-2 standard, after a car has been left idle in cold temperatures, and the car engine is started, the 24-volt battery voltage will drop as low as 6 volts. The low dump occurs when the battery is disconnected from the alternator, while the battery is being charged, causing a surge in the power line. 

After shunting the surge with a transient suppressor, in many cases, the regular first stage buck converter has to absorb more energy than what the nominal battery voltage requires. The wide input range of the first stage buck converter prevents damage to the telematic system downstream during the over voltage transients. Normally, the battery voltage will be clamped to 57 volts in a 24-volt battery system, and a 60-volt input converter will be suitable for this application. 

Typically, telematic systems require extremely light load operation, because the system is always on, even though the vehicle is off. The total system power will require less than 100 mic grams, even as low as 65 mic grams when the converter is unloaded. And when its GPS module is on, the constant current load is nearly 1 amp, and the peak current will reach 5 amps, when transmitting a signal. The LM76005-Q1 is a 3.5 to 60 volt 5 amp synchronous buck converter. 

This device uses internal compensation and an internal MOSFET and, ultimately, only requires 7 external passive components in default operation. The LM76005-Q1 can achieve greater than 90% efficiency in full load with its internal high efficiency power switches and low switching losses. In addition, this device uses pulse skip modulation operation to keep the quiescent current within 15 mic grams in standby mode, which allows the LM76005-Q1 to maintain a high efficiency for always on systems to extend the life of the battery. 

Automotive applications require high reliability for the circuitry to last at least 10 years. There are often specifications for board level reliability and temperature cycling in the excess of 1,000 cycles. Traditional QFN packages have the risk of limited side wetting, and poor soldering on the lead. Texas Instruments uses wettable flank packages to guarantee side wetting at good solder joints, with 100% visual inspection possible to improve reliability and save in system cost. 

The LM76005-Q1 is in a 4 millimeter cross 6 millimeter 30 pin WQFN package, with a thermal pad and wettable flanks. It can achieve a high reliability, and also an excellent thermal performance due to the large thermal flank. Typically, the ambient temperature is specified to go up to 105 degrees C for the telematic system. This is due to the 85 degrees C maximum temperature of the environment plus 20 degrees C when inside the shielding box. 

And the worst case of thermal dissipation is going to occur at high input voltages during load dump. For the purpose of calculating the thermal resistance, the maximum current capability of the LM76005-Q1 was used. At an input voltage of 57 volts, and an output voltage of 4 volts, and a 5 amp load, the efficiency will reach approximately 84% at high ambient temperatures, and the associated power loss is about 3.2 watts. 

With the temperature rise, the thermal resistance, r theta ja, is only 18.8 degrees C per watt. In addition, the LM76005-Q1 can easily pass the automotive CISPR25 Class 5 standard, for both the peak and average EMI limits. With this optimized switching edges, this data was taken without any external shielding. 

In summary, when designing a telematic system, the key advantages of the LM76005 are that this device provides a wide input voltage range to cover the battery transients, a wettable flank QFN package for 100% visual inspection, although thermal resistance of 18 degrees C per watt, and EMI performance that can meet the low EMI standard for automotive DISPR25 Class 5 limits without any external shielding. For more information on the automotive telematic system and Texas Instruments system level solutions, please follow the links that you find on this slide. Thank you for listening to this presentation.