Generating High DC Output Voltage from Low Input Supply

Whether for driving white LED backlights or powering RF and analog circuits, laptops, tablets and other mobile devices often require voltages that are much higher than the input supply voltage. Consequently, step-up or boost DC/DC converters generate output voltages that are several times the input to serve a variety of circuits and functions in these systems. For instance, in battery powered systems, the input normally is 5 V and below, while voltages as high as 15 and 24 V or more are needed to power RF/analog functions or drive thin-film transistor (TFT) liquid crystal displays (LCDs). Similarly, high voltages also are needed to bias avalanche photodiodes (APDs) found in optical receivers.

To address these needs, Analog Devices has added two low-voltage DC/DC boost converters to its portfolio of products. The ADP1612 and ADP1613 DC/DC converters enable designers to boost input voltage as low as 1.8 V to output voltage as high as 20 V. When combined with thin-profile packaging and high-switching-frequency operation, these DC/DC converters increase battery run times in portable applications where low power consumption is essential and PC-board space is at a premium.
While ADP1612 supports an input DC voltage range of 1.8 to 5.5 V, the ADP1613 handles an input DC range of 2.5 to 5.5 V. The adjustable output voltage allows the boost converters to extend battery life with unregulated input voltage operation. The boost converters use a pulse-width modulated (PWM) current-mode architecture to regulate the output voltage across load conditions and to help reduce the risk of in-rush currents at startup. As a result, the devices are able to deliver up to 94 percent efficiency with fast transient response and stable output voltage levels for greater system reliability.
A typical application circuit for the boost converters is depicted in Figure 1. Both the ADP1612 and ADP1613 can operate at 650 kHz or 1.3 MHz. While the higher switching frequency allows the use of a smaller inductor, efficiency drops by approximately 2 percent with every doubling of the switching frequency. In these converters, the switching frequency is pin-selectable. For 650-kHz operation, the FREQ pin is connected to ground (GND) or to pin V_IN for 1.3 MHz operation.
 
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