Datasheet LTC3401 (Analog Devices) - 9

LTC3401
U U W U APPLICATIO S I FOR ATIO
Burst Mode operation is user controlled by driving the MODE/SYNC pin high to enable and low to disable. It is Rt SHDN MODE VC recommended that Burst Mode operation be entered after VIN FB SW VOUT the part has started up. GND PGOOD
COMPONENT SELECTION
VOUT
Inductor Selection
The high frequency operation of the LTC3401 allows the 3401 F01 use of small surface mount inductors. The minimum
Figure 1. Recommended Component Placement. Traces
inductance value is proportional to the operating fre-
Carrying High Current Are Direct. Trace Area FB and VC Pins
quency and is limited by the following constraints:
Are Kept Low. Lead Length to Battery Should be Kept Short
V • V – V
Output Capacitor Selection
3 IN MIN ( ) OUT MAX ( ) IN M ( IN ( )) L > H μ and L > H The output voltage ripple has several components. The f f • Ripple • VOUT MAX ( ) bulk value of the capacitor is set to reduce the ripple due where to charge into the capacitor each cycle. The max ripple due f = Operating Frequency (Hz) to charge is given by: Ripple = Allowable Inductor Current Ripple (A) I V VR P IN = • V V BULK IN(MIN) = Minimum Input Voltage (V) C • V • f OUT OUT VOUT(MAX) = Maximum Output Voltage (V) where The inductor current ripple is typically set to 20% to 40% IP = Peak Inductor Current of the maximum inductor current. The ESR can be a significant factor for ripple in most power For high efficiency, choose an inductor with a high fre- converters. The ripple due to capacitor ESR is simply given quency core material, such as ferrite, to reduce core by: losses. The inductor should have low ESR (equivalent series resistance) to reduce the I2R losses and must be VRCESR = IP • RESR V able to handle the peak inductor current at full load without where saturating. Molded chokes or chip inductors usually do R not have enough core to support the peak inductor cur- ESR = Capacitor Series Resistance rents in the 1A to 2A region. To minimize radiated noise, Low ESR capacitors should be used to minimize output use a toroid, pot core or shielded bobbin inductor. See voltage ripple. For surface mount applications, AVX TPS Table 1 for a list of component suppliers. series tantalum capacitors, Sanyo POSCAP, or Taiyo- Yuden ceramic capacitors are recommended. For through-
Table 1. Inductor Vendor Information
hole applications Sanyo OS-CON capacitors offer low ESR
SUPPLIER PHONE FAX WEBSITE
in a small package size. See Table 2 for a list of component Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com suppliers. Coiltronics (516) 241-7876 (516) 241-9339 www.coiltronics.com
Table 2. Capacitor Vendor Information
Murata (814) 237-1431 (814) 238-0490 www.murata.com
SUPPLIER PHONE FAX WEBSITE
(800) 831-9172 AVX (803) 448-9411 (803) 448-1943 www.avxcorp.com Sumida USA: (847) 956-0666 (847) 956-0702 www.japanlink.com Sanyo (619) 661-6322 (619) 661-1055 www.sanyovideo.com Japan: 81-3-3607-5111 81-3-3607-5144 sumida Taiyo Yuden (408) 573-4150 (408) 573-4159 www.t-yuden.com 3401fb 9