With the increasing popularity of modern car sales, the automotive industry's process development has also improved qualitatively, but the requirements for automotive power supply systems are increasingly responsible. Everyone knows that there is a special automotive voltage regulator in the power supply system of the car. Nowadays, with the improvement of the automobile manufacturing process, a better requirement for the buck-type applicable performance used in the automotive power supply system is undoubtedly put forward.
The following is a description of Linear Technology's step-down regulator LTC7138 for automotive environments. The LTC7138 is a 400mA step-down regulator that operates from an input voltage range of 4V to 140V, making it ideal for industrial, telecommunications, and Automotive and other applications that are often subjected to severe voltage transients. Since the regulator uses a hysteresis architecture, no external compensation is required. The output voltage can be set to 1.8V, 3.3V or 5.0V using the pin, or, if an external voltage divider is used, the output can be adjusted from 0.8V to VIN. With an internal P-channel FET, 100% duty cycle operation is possible. The LTC7138 is packaged in a thermally enhanced high voltage (some pins are removed) MSOP package.
1. Simple 5V/400mA step-down with wide VIN range
Figure 1 shows a 5V step-down converter with a maximum input voltage of 140V and using only four external components. Set the output to 5V by connecting the VPRG1 pin to the SS pin and VPRG2 to ground. This device does not require any external compensation.
Figure 1: High Efficiency 5V, 400mA Step-Down Regulator
Figure 2: Efficiency of the regulator shown in Figure 1.
High efficiency is maintained over a wide load range, thanks in part to the LTC7138's Burst Mode® operation and 12μA unloaded IQ current. With a 12V input, the efficiency peaks up to 87% for a 10mA load and over 80% at a load as low as 0.4mA. This level of energy savings makes it ideal for battery-powered systems that are always on.
2. 24V/800mA step-down using two parallel LTC7138s
Figure 3 shows the situation where two LTC7138s are connected in parallel to provide a 24V/800mA output. Parallel operation is accomplished by connecting the feedback comparator output pin (FBO) of the master to the VFB pin of the slave. In this setup, the slave will follow the master to enter and exit the burst cycle (see Figure 4). The output of the 24V buck converter is set with an external feedback divider. When using a 48V input, the regulator's full load efficiency is 93.6% (Figure 5).
Figure 3: High efficiency 24V, 800mA step-down with two parallel LTC7138s
Figure 4: 24V, 800mA Step-Down Converter Operating in Parallel (at VIN = 140V, IOUT = 600mA)
Figure 5: Efficiency of the regulator shown in Figure 3.
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