Datasheet LT1944 (Analog Devices) - 6
| Fabricante | Analog Devices |
| Descripción | Dual Micropower Step-Up DC/DC Converter |
| Páginas / Página | 8 / 6 — APPLICATIO S I FOR ATIO. Setting the Output Voltage. Capacitor Selection. … |
| Formato / tamaño de archivo | PDF / 168 Kb |
| Idioma del documento | Inglés |
APPLICATIO S I FOR ATIO. Setting the Output Voltage. Capacitor Selection. Diode Selection. Lowering Output Voltage Ripple
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LT1944
U U W U APPLICATIO S I FOR ATIO
limited to 350mA, the power switch of the LT1944 can
Setting the Output Voltage
handle larger currents without problem, but the overall Set the output voltage for each switching regulator by efficiency will suffer. Best results will be obtained when choosing the appropriate values for feedback resistors R1 IPEAK is kept below 700mA for the LT1944. and R2 (see Figure 1).
Capacitor Selection
V R = R OUT 1 2 − 1 Low ESR (Equivalent Series Resistance) capacitors should 1 2 V 3 . be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are the best choice, as they
Diode Selection
have a very low ESR and are available in very small packages. Their small size makes them a good companion For most LT1944 applications, the Motorola MBR0520 to the LT1944’s MS10 package. Solid tantalum capacitors surface mount Schottky diode (0.5A, 20V) is an ideal (like the AVX TPS, Sprague 593D families) or OS-CON choice. Schottky diodes, with their low forward voltage capacitors can be used, but they will occupy more board drop and fast switching speed, are the best match for the area than a ceramic and will have a higher ESR. Always use LT1944. For higher output voltage applications the 30V a capacitor with a sufficient voltage rating. MBR0530 or 40V MBR0540 can be used. Many different manufacturers make equivalent parts, but make sure that Ceramic capacitors also make a good choice for the input the component is rated to handle at least 0.35A. decoupling capacitor, which should be placed as close as possible to the LT1944. A 4.7µF input capacitor is suffi-
Lowering Output Voltage Ripple
cient for most applications. Table 2 shows a list of several Using low ESR capacitors will help minimize the output capacitor manufacturers. Consult the manufacturers for ripple voltage, but proper selection of the inductor and the more detailed information and for their entire selection of output capacitor also plays a big role. The LT1944 pro- related parts. vides energy to the load in bursts by ramping up the
Table 2. Recommended Capacitors
inductor current, then delivering that current to the load.
CAPACITOR TYPE VENDOR
If too large of an inductor value or too small of a capacitor Ceramic Taiyo Yuden value is used, the output ripple voltage will increase (408) 573-4150 because the capacitor will be slightly overcharged each www.t-yuden.com burst cycle. To reduce the output ripple, increase the Ceramic AVX (803) 448-9411 output capacitor value or add a 4.7pF feed-forward capaci- www.avxcorp.com tor in the feedback network of the LT1944 (see the circuits Ceramic Murata in the Typical Applications section). Adding this small, (714) 852-2001 inexpensive 4.7pF capacitor will greatly reduce the output www.murata.com voltage ripple. 6
U U W U APPLICATIO S I FOR ATIO
limited to 350mA, the power switch of the LT1944 can
Setting the Output Voltage
handle larger currents without problem, but the overall Set the output voltage for each switching regulator by efficiency will suffer. Best results will be obtained when choosing the appropriate values for feedback resistors R1 IPEAK is kept below 700mA for the LT1944. and R2 (see Figure 1).
Capacitor Selection
V R = R OUT 1 2 − 1 Low ESR (Equivalent Series Resistance) capacitors should 1 2 V 3 . be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are the best choice, as they
Diode Selection
have a very low ESR and are available in very small packages. Their small size makes them a good companion For most LT1944 applications, the Motorola MBR0520 to the LT1944’s MS10 package. Solid tantalum capacitors surface mount Schottky diode (0.5A, 20V) is an ideal (like the AVX TPS, Sprague 593D families) or OS-CON choice. Schottky diodes, with their low forward voltage capacitors can be used, but they will occupy more board drop and fast switching speed, are the best match for the area than a ceramic and will have a higher ESR. Always use LT1944. For higher output voltage applications the 30V a capacitor with a sufficient voltage rating. MBR0530 or 40V MBR0540 can be used. Many different manufacturers make equivalent parts, but make sure that Ceramic capacitors also make a good choice for the input the component is rated to handle at least 0.35A. decoupling capacitor, which should be placed as close as possible to the LT1944. A 4.7µF input capacitor is suffi-
Lowering Output Voltage Ripple
cient for most applications. Table 2 shows a list of several Using low ESR capacitors will help minimize the output capacitor manufacturers. Consult the manufacturers for ripple voltage, but proper selection of the inductor and the more detailed information and for their entire selection of output capacitor also plays a big role. The LT1944 pro- related parts. vides energy to the load in bursts by ramping up the
Table 2. Recommended Capacitors
inductor current, then delivering that current to the load.
CAPACITOR TYPE VENDOR
If too large of an inductor value or too small of a capacitor Ceramic Taiyo Yuden value is used, the output ripple voltage will increase (408) 573-4150 because the capacitor will be slightly overcharged each www.t-yuden.com burst cycle. To reduce the output ripple, increase the Ceramic AVX (803) 448-9411 output capacitor value or add a 4.7pF feed-forward capaci- www.avxcorp.com tor in the feedback network of the LT1944 (see the circuits Ceramic Murata in the Typical Applications section). Adding this small, (714) 852-2001 inexpensive 4.7pF capacitor will greatly reduce the output www.murata.com voltage ripple. 6