Datasheet LT8415 (Analog Devices) - 8

LT8415
APPLICATIONS INFORMATION Inductor Selection
capacitor placed on the CAP node is recommended to filter Several inductors that work well with the LT8415 are listed the inductor current while a 0.1μF to 1μF capacitor placed in Table 1. The tables are not complete, and there are many on the VOUT node will give excellent transient response other manufacturers and devices that can be used. Consult and stability. To make the VREF pin less sensitive to noise, each manufacturer for more detailed information and for putting a capacitor on the VREF pin is recommended, but their entire selection of related parts, as many different not required. A 47nF to 220nF 0402 capacitor will be suf- sizes and shapes are available. ficient. See also Soft-Start section for more information about a capacitor across VREF. Table 2 shows a list of several Inductors with a value of 47μH or higher are recommended capacitor manufacturers. Consult the manufacturers for for most LT8415 designs. Inductors with low core losses more detailed information and for their entire selection and small DCR (copper wire resistance) are good choices of related parts. for LT8415 applications. For full output power, the induc-
Table 2. Recommended Ceramic Capacitor Manufacturers
tor should have a saturation current rating higher than the peak inductor current. The peak inductor current can be
MANUFACTURER PHONE WEBSITE
calculated as: Taiyo Yuden (408) 573-4150 www.t-yuden.com Murata (814) 237-1431 www.murata.com AVX (843) 448-9411 www.avxcorp.com I VIN •150 •10−6 PK = ILIMIT + mA Kemet (408)986-0424 www.kemet.com L TDK (847) 803-6100 www.tdk.com where the worst case ILIMIT is 30mA. L is the inductance value in Henrys and V
Setting Output Voltage
IN is the input voltage to the boost circuit. The output voltage is set by the FBP pin voltage, and VOUT
Table 1. Recommended Inductors for LT8415
is equal to 31.85 • VFBP when the output is regulated,
L DCR SIZE
shown in Figure 1. Since the VREF pin provides a good
PART (µH) (µH) (mm) VENDOR
reference (~1.235V), the FBP voltage can be easily set by LQH2MCN680K02 68 6.6 2.0 × 1.6 × 0.9 Murata a resistor divider from the V LQH32CN101K53 100 3.5 3.2 REF pin to ground. The series × 2.5 × 2.0 www.murata.com resistance of this resistor divider should be kept larger than DO2010-683ML 68 8.8 2.0 × 2.0 × 1.0 Coilcraft DO2010-104ML 100 15.7 2.0 200KΩ to prevent loading down the V × 2.0 × 1.0 www.coilcraft.com REF pin. The FBP pin LPS3015-104ML 100 3.4 3.0 × 3.0 × 1.4 can also be biased directly by an external reference. For LPS3015-154ML 150 6.1 3.0 × 3.0 × 1.4 over voltage protection, the output voltage is limited to 40V. Therefore, if VFBP is higher than 1.235V, the output
Capacitor Selection
voltage will stay at 40V. 50 The small size and low ESR of ceramic capacitors make them suitable for most LT8415 applications. X5R and 40 X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges 30 than other types such as Y5V or Z5U. A 2.2μF or higher TAGE (V) input capacitor and a 0.1μF to 1μF output capacitor are 20 sufficient for most applications. Always use a capacitor OUTPUT VOL with a sufficient voltage rating. Many ceramic capacitors 10 rated at 0.1μF to 1μF have greatly reduced capacitance when bias voltages are applied. Be sure to check actual 0 0 0.5 1 1.5 2 capacitance at the desired output voltage. Generally a 0603 FBP VOLTAGE (V) or 0805 size capacitor will be adequate. A 0.1μF to 1μF 8415 F01
Figure 1. FBP to VOUT Transfer Curve
8415fb 8 For more information www.linear.com/LT8415