One of the latest Linear Technology dc-to-dc converter ICs is the LTC3124, whose application circuit is shown in Fig. 1.
Fig. 1. The LTC3124features fixed frequency, current mode PWM control for good line and load regulation as well as Burst Mode control that improves efficiency at light loads and reduces standby current at no load.
The regulator employs an external resistive voltage divider from VOUT to FB to SGND to program the output from 2.5 V to 15 V. When set for a 12 V output, it can deliver up to 1.5 A continuously from a 5 V input. Its 2.5 A per phase current limit, along with the ability to program output voltages up to 15 V, make the IC suitable for a variety of applications.
The use of two phases equally spaced 180° apart, doubles output ripple frequency, and significantly reduces output capacitor ripple current. Although this architecture requires two inductors, rather than a single inductor, it has several important advantages:
• Substantially lower peak inductor current allows the use of smaller, lower cost inductors.
• Significantly reduced output ripple current minimizes output capacitance requirement.
• Higher frequency output ripple is easier to filter for low noise applications.
• Input ripple current is also reduced for lower noise on VIN.
With two-phase operation, one phase always delivers current to the load whenever VIN is greater than one-half VOUT (for duty cycles less than 50%). As the duty cycle decreases further, load current delivery between the two phases begin to overlap, occurring simultaneously for a growing portion of each phase as the duty cycle approaches zero. Compared with a single-phase converter this significantly reduces both the output ripple current and the peak current in each inductor.
The LTC3124 provides an advantage for battery-powered systems, it can start up from inputs as low as 1.8 V and continue to operate from inputs as low as 0.5 V, while producing output voltages greater than 2.5 V. This extends operating times by maximizing the amount of energy extracted from the input source. The limiting factors for the application are the ability of the power source to supply sufficient power to the output at the low input voltage, and the maximum duty cycle, which is clamped at 94%. At low input voltages, small voltage drops due to series resistance become critical and limit the converter’s power delivery.
Even if the input voltage exceeds the output voltage, the IC will regulate the output, enabling compatibility with any battery chemistry. The LTC3124 is an ideal solution for boost applications requiring outputs up to 15 V where high efficiency, small size and high reliability are defining factors.
source: http://powerelectronics.com/dc-dc-converters/two-phase-synchronous-boost-regulator-ic-delivers-15-v
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