Datasheet LT3663 (Analog Devices) - 10

LT3663
applicaTions inForMaTion BOOST and BIAS Pin Considerations
boost diode. For reliable BOOST pin operation with 2.5V Capacitor C3 and the internal boost diode (see the Block outputs use a good external Schottky diode (such as the Diagram) are used to generate a boost voltage that is higher ON Semi, MBR0540) and a 1µF boost capacitor (see Figure than the input voltage. In most cases a 0.1µF capacitor 4b). For lower output voltages connect an external Schottky works wel . Figure 4 shows three ways to arrange the boost diode to the input (Figure 4c), or to another supply greater circuit. The BOOST pin must be more than 2.3V above the than 2.8V. Using VIN reduces the maximum input voltage SW pin for best efficiency. For outputs of 3V and above, the to 25V. The circuit in Figure 4a is more efficient because standard circuit (Figure 4a) is best. For outputs between the BOOST pin current comes from a lower voltage source. 2.8V and 3V, use a 1µF boost capacitor. A 2.5V output Take care to ensure that the maximum voltage ratings of presents a special case because it is marginal y adequate the BOOST pin is not exceeded. to support the boosted drive stage while using the internal VIN VIN BOOST VIN VIN BOOST C3 C3 SW SW LT3663 LT3663 D3 ISENSE ISENSE VOUT VOUT VOUT VOUT
(4a) For VOUT > 2.8V (4b) For 2.5V < VOUT < 2.8V
D3 VIN VIN BOOST C3 SW LT3663 ISENSE VOUT VOUT 3663 F04
(4c) For VOUT < 2.5V; VIN(MAX) = 25V Figure 4. Three Circuits to Generate BOOST Pin Voltage
3663fc 10 For more information www.linear.com/LT3663 Document Outline Description Typical Application Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Operation Applications Information Package Description