Datasheet LT1933 (Analog Devices) - 9
| Hersteller | Analog Devices |
| Beschreibung | 600mA, 500kHz Step-Down Switching Regulator in SOT-23 and DFN Packages |
| Seiten / Seite | 20 / 9 — APPLICATIONS INFORMATION. Output Capacitor. Table 2.Inductor Vendors. … |
| Dateiformat / Größe | PDF / 371 Kb |
| Dokumentensprache | Englisch |
APPLICATIONS INFORMATION. Output Capacitor. Table 2.Inductor Vendors. Vendor. Phone. URL. Part Series. Comments
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LT1933
APPLICATIONS INFORMATION
switching current into a tight local loop, minimizing EMI. Ceramic capacitors have very low equivalent series re- A 2.2μF capacitor is capable of this task, but only if it is sistance (ESR) and provide the best ripple performance. placed close to the LT1933 and the catch diode; see the A good value is PCB Layout section. A second precaution regarding the C ceramic input capacitor concerns the maximum input OUT = 60/VOUT voltage rating of the LT1933. A ceramic input capacitor where COUT is in μF. Use X5R or X7R types, and keep combined with trace or cable inductance forms a high in mind that a ceramic capacitor biased with VOUT will quality (under damped) tank circuit. If the LT1933 circuit have less than its nominal capacitance. This choice will is plugged into a live supply, the input voltage can ring to provide low output ripple and good transient response. twice its nominal value, possibly exceeding the LT1933’s Transient performance can be improved with a high value voltage rating. This situation is easily avoided; see the Hot capacitor, but a phase lead capacitor across the feedback Plugging Safely section. resistor R1 may be required to get the full benefi t (see the Compensation section).
Output Capacitor
High performance electrolytic capacitors can be used for The output capacitor has two essential functions. Along the output capacitor. Low ESR is important, so choose one with the inductor, it fi lters the square wave generated that is intended for use in switching regulators. The ESR by the LT1933 to produce the DC output. In this role it should be specifi ed by the supplier, and should be 0.1Ω determines the output ripple, and low impedance at the or less. Such a capacitor will be larger than a ceramic switching frequency is important. The second function capacitor and will have a larger capacitance, because the is to store energy in order to satisfy transient loads and capacitor must be large to achieve low ESR. Table 2 lists stabilize the LT1933’s control loop. several capacitor vendors.
Table 2.Inductor Vendors Vendor Phone URL Part Series Comments
Panasonic (714) 373-7366 www.panasonic.com Ceramic, Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum T494, T495 Sanyo (408) 749-9714 www.sanyovideo.com Ceramic, Polymer, POSCAP Tantalum Murata (404)436-1300 www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden (864)963-6300 www.taiyo-yuden.com Ceramic 1933fe 9
APPLICATIONS INFORMATION
switching current into a tight local loop, minimizing EMI. Ceramic capacitors have very low equivalent series re- A 2.2μF capacitor is capable of this task, but only if it is sistance (ESR) and provide the best ripple performance. placed close to the LT1933 and the catch diode; see the A good value is PCB Layout section. A second precaution regarding the C ceramic input capacitor concerns the maximum input OUT = 60/VOUT voltage rating of the LT1933. A ceramic input capacitor where COUT is in μF. Use X5R or X7R types, and keep combined with trace or cable inductance forms a high in mind that a ceramic capacitor biased with VOUT will quality (under damped) tank circuit. If the LT1933 circuit have less than its nominal capacitance. This choice will is plugged into a live supply, the input voltage can ring to provide low output ripple and good transient response. twice its nominal value, possibly exceeding the LT1933’s Transient performance can be improved with a high value voltage rating. This situation is easily avoided; see the Hot capacitor, but a phase lead capacitor across the feedback Plugging Safely section. resistor R1 may be required to get the full benefi t (see the Compensation section).
Output Capacitor
High performance electrolytic capacitors can be used for The output capacitor has two essential functions. Along the output capacitor. Low ESR is important, so choose one with the inductor, it fi lters the square wave generated that is intended for use in switching regulators. The ESR by the LT1933 to produce the DC output. In this role it should be specifi ed by the supplier, and should be 0.1Ω determines the output ripple, and low impedance at the or less. Such a capacitor will be larger than a ceramic switching frequency is important. The second function capacitor and will have a larger capacitance, because the is to store energy in order to satisfy transient loads and capacitor must be large to achieve low ESR. Table 2 lists stabilize the LT1933’s control loop. several capacitor vendors.
Table 2.Inductor Vendors Vendor Phone URL Part Series Comments
Panasonic (714) 373-7366 www.panasonic.com Ceramic, Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum T494, T495 Sanyo (408) 749-9714 www.sanyovideo.com Ceramic, Polymer, POSCAP Tantalum Murata (404)436-1300 www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden (864)963-6300 www.taiyo-yuden.com Ceramic 1933fe 9