Datasheet LT1934, LT1934 (Analog Devices) - 10
| Fabricante | Analog Devices |
| Descripción | Micropower Step-Down Switching Regulators in ThinSOT |
| Páginas / Página | 20 / 10 — APPLICATIONS INFORMATION. Output Capacitor and Output Ripple. Ceramic … |
| Formato / tamaño de archivo | PDF / 245 Kb |
| Idioma del documento | Inglés |
APPLICATIONS INFORMATION. Output Capacitor and Output Ripple. Ceramic Capacitors. Table 3. Capacitor Vendors. VENDOR. PHONE URL
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- LT1934EDCB#PBF LT1934EDCB#TRMPBF LT1934EDCB#TRPBF LT1934EDCB-1#PBF LT1934EDCB-1#TRMPBF LT1934EDCB-1#TRPBF LT1934ES6#TRMPBF LT1934ES6#TRPBF LT1934ES6-1#TRMPBF LT1934ES6-1#TRPBF LT1934IDCB#PBF LT1934IDCB#TRMPBF LT1934IDCB#TRPBF LT1934IDCB-1#PBF LT1934IDCB-1#TRMPBF LT1934IDCB-1#TRPBF LT1934IS6#PBF LT1934IS6#TRMPBF LT1934IS6#TRPBF LT1934IS6-1#PBF LT1934IS6-1#TRMPBF LT1934IS6-1#TRPBF
Versión de texto del documento
LT1934/LT1934-1
APPLICATIONS INFORMATION
capacitor is subject to large surge currents if the LT1934 The LT1934-1, with its lower switch current, can use a circuit is connected to a low impedance supply, and that B-case tantalum capacitor. some electrolytic capacitors (in particular tantalum) must With a high quality capacitor fi ltering the ripple current be specifi ed for such use. from the inductor, the output voltage ripple is determined by the hysteresis and delay in the LT1934’s feedback
Output Capacitor and Output Ripple
comparator. This ripple can be reduced further by adding The output capacitor fi lters the inductor’s ripple current and a small (typically 10pF) phase lead capacitor between the stores energy to satisfy the load current when the LT1934 output and the feedback pin. is quiescent. In order to keep output voltage ripple low, the impedance of the capacitor must be low at the LT1934’s
Ceramic Capacitors
switching frequency. The capacitor’s equivalent series Ceramic capacitors are small, robust and have very low resistance (ESR) determines this impedance. Choose one ESR. However, ceramic capacitors can cause problems with low ESR intended for use in switching regulators. The when used with the LT1934. contribution to ripple voltage due to the ESR is approxi- mately I Not all ceramic capacitors are suitable. X5R and X7R LIM • ESR. ESR should be less than ~150mΩ for the LT1934 and less than ~500mΩ for the LT1934-1. types are stable over temperature and applied voltage and give dependable service. Other types (Y5V and Z5U) The value of the output capacitor must be large enough have very large temperature and voltage coeffi cients of to accept the energy stored in the inductor without a large capacitance. In the application circuit they may have only change in output voltage. Setting this voltage step equal to a small fraction of their nominal capacitance and voltage 1% of the output voltage, the output capacitor must be: ripple may be much larger than expected. COUT > 50 • L • (ILIM/VOUT)2 Ceramic capacitors are piezoelectric. The LT1934’s switch- For example, an LT1934 producing 3.3V with L = 47μH ing frequency depends on the load current, and at light requires 33μF. This value can be relaxed if small circuit loads the LT1934 can excite the ceramic capacitor at audio size is more important than low output ripple. frequencies, generating audible noise. If this is unaccept- able, use a high performance electrolytic capacitor at the Sanyo’s POSCAP series in B-case and C-case sizes output. The input capacitor can be a parallel combination provides very good performance in a small package for of a 2.2μF ceramic capacitor and a low cost electrolytic the LT1934. Similar performance in traditional tantalum capacitor. The level of noise produced by the LT1934-1 capacitors requires a larger package (C- or D-case).
Table 3. Capacitor 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 1934fe 10
APPLICATIONS INFORMATION
capacitor is subject to large surge currents if the LT1934 The LT1934-1, with its lower switch current, can use a circuit is connected to a low impedance supply, and that B-case tantalum capacitor. some electrolytic capacitors (in particular tantalum) must With a high quality capacitor fi ltering the ripple current be specifi ed for such use. from the inductor, the output voltage ripple is determined by the hysteresis and delay in the LT1934’s feedback
Output Capacitor and Output Ripple
comparator. This ripple can be reduced further by adding The output capacitor fi lters the inductor’s ripple current and a small (typically 10pF) phase lead capacitor between the stores energy to satisfy the load current when the LT1934 output and the feedback pin. is quiescent. In order to keep output voltage ripple low, the impedance of the capacitor must be low at the LT1934’s
Ceramic Capacitors
switching frequency. The capacitor’s equivalent series Ceramic capacitors are small, robust and have very low resistance (ESR) determines this impedance. Choose one ESR. However, ceramic capacitors can cause problems with low ESR intended for use in switching regulators. The when used with the LT1934. contribution to ripple voltage due to the ESR is approxi- mately I Not all ceramic capacitors are suitable. X5R and X7R LIM • ESR. ESR should be less than ~150mΩ for the LT1934 and less than ~500mΩ for the LT1934-1. types are stable over temperature and applied voltage and give dependable service. Other types (Y5V and Z5U) The value of the output capacitor must be large enough have very large temperature and voltage coeffi cients of to accept the energy stored in the inductor without a large capacitance. In the application circuit they may have only change in output voltage. Setting this voltage step equal to a small fraction of their nominal capacitance and voltage 1% of the output voltage, the output capacitor must be: ripple may be much larger than expected. COUT > 50 • L • (ILIM/VOUT)2 Ceramic capacitors are piezoelectric. The LT1934’s switch- For example, an LT1934 producing 3.3V with L = 47μH ing frequency depends on the load current, and at light requires 33μF. This value can be relaxed if small circuit loads the LT1934 can excite the ceramic capacitor at audio size is more important than low output ripple. frequencies, generating audible noise. If this is unaccept- able, use a high performance electrolytic capacitor at the Sanyo’s POSCAP series in B-case and C-case sizes output. The input capacitor can be a parallel combination provides very good performance in a small package for of a 2.2μF ceramic capacitor and a low cost electrolytic the LT1934. Similar performance in traditional tantalum capacitor. The level of noise produced by the LT1934-1 capacitors requires a larger package (C- or D-case).
Table 3. Capacitor 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 1934fe 10