Datasheet
SLUS489 − OCTOBER 2001
24
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APPLICATION INFORMATION
Table 1. SMT Commercial Inductor Manufacturers
Coilcraft Inc. (800) 322−2645 1102 Silver Lake RD, Cary, IL 60013
Coiltronics Inc. (407) 241−7876 6000 Park of Commerce Blvd, Boca Raton, FL 33487
Dale Electronics, Inc. (605) 665−9301 East Highway 50, Yankton, SD 57078
Pulse Engineering Ltd. (204) 633−432 1300 Keewatin Street, Winnipeg, MB R2X 2R9
Sumida
1−847−545−6700
Fax 1−847−545−6720
1701 Golf Road, Tower 3, Suite 400,
Rolling Meadows, IL 60008
BH Electronics (612) 894−9590 12219 Wood Lake Drive, Burnsville, MN 55337
Tokin America Inc. (408) 432−8020 155 Nicholson Lane, San Jose CA 95134
selecting the filter capacitor
The input and output filter capacitors must have low ESR and low ESL. Surface-mount tantalum, OSCONs or
multilayer ceramics (MLCs) are recommended. The capacitor selected must have the proper ripple current
rating for the application. Some recommended capacitor types are listed in Table 2.
Table 2. Recommended SMT Filter Capacitors
Manufacturer Part Number Features
AVX TPS series Low ESR tantalum
Kemet T410 series Low ESR tantalum
Murata GRM series Low ESR ceramic
Sanyo OSCON series Low ESR organic
Sprague
591D series Low ESR, low profile tantalum
Sprague
594D series Low ESR tantalum
Tokin Y5U, Y5V Type Low ESR ceramic
Taiyo Yuden X5R Type Low ESR ceramic
circuit layout and grounding
As with any high-frequency switching power supply, circuit layout, hookup, and grounding are critical for proper
operation. Although this may be a relatively low-power, low-voltage design, these issues are still very important.
The MOSFET turn-on and turn-off times necessary to maintain high efficiency at high switching frequencies of
1 MHz or more result in high dv/dt and di/dts. This makes stray circuit inductance especially critical. In addition,
the high impedances associated with low-power designs, such as in the feedback divider, make them especially
susceptible to noise pickup.
layout
The component layout should be as tight as possible to minimize stray inductance. This is especially true of the
high-current paths, such as in series with the MOSFETs and the input and output filter capacitors.
The components associated with the feedback, compensation and timing should be kept away from the power
components (MOSFETs, inductor). Keep all components as close to the device pins as possible. Nodes that
are especially noise sensitive are the FB, RT and COMP pins.