Datasheet LT1944-1 (Analog Devices) - 6
| Manufacturer | Analog Devices |
| Description | Dual Micropower Step-Up DC/DC Converter |
| Pages / Page | 8 / 6 — APPLICATIO S I FOR ATIO. Setting the Output Voltage. Capacitor Selection. … |
| File Format / Size | PDF / 151 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Setting the Output Voltage. Capacitor Selection. Diode Selection. Lowering Output Voltage Ripple
Model Line for this Datasheet
Text Version of Document
LT1944-1
U U W U APPLICATIO S I FOR ATIO
limited to 100mA (or 175mA), the power switch of the
Setting the Output Voltage
LT1944-1 can handle larger currents without problem, but Set the output voltage for each switching regulator by the overall efficiency will suffer. Best results will be ob- choosing the appropriate values for feedback resistors R1 tained when IPEAK is kept below 400mA for the LT1944-1. and R2 (see Figure 1).
Capacitor Selection
V OUT Low ESR (Equivalent Series Resistance) capacitors should R1= R2 − 1 1 2 V 3 . be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are the best choice, as they have a very low ESR and are available in very small
Diode Selection
packages. Their small size makes them a good companion For most LT1944-1 applications, the Philips BAT54 or to the LT1944-1’s MS10 package. Solid tantalum capaci- Central Semiconductor CMDSH-3 surface mount Schottky tors (like the AVX TPS, Sprague 593D families) or OS-CON diodes are an ideal choice. Schottky diodes, with their low capacitors can be used, but they will occupy more board forward voltage drop and fast switching speed, are the area than a ceramic and will have a higher ESR. Always use best match for the LT1944-1. Many different manufactur- a capacitor with a sufficient voltage rating. ers make equivalent parts, but make sure that the compo- Ceramic capacitors also make a good choice for the input nent is rated to handle at least 100mA. decoupling capacitor, which should be placed as close as
Lowering Output Voltage Ripple
possible to the LT1944-1. A 4.7µF input capacitor is sufficient for most applications. Table 2 shows a list of Using low ESR capacitors will help minimize the output several capacitor manufacturers. Consult the manufactur- ripple voltage, but proper selection of the inductor and the ers for more detailed information and for their entire output capacitor also plays a big role. The LT1944-1 selection of related parts. provides energy to the load in bursts by ramping up the inductor current, then delivering that current to the load.
Table 2. Recommended Capacitors
If too large of an inductor value or too small of a capacitor
CAPACITOR TYPE VENDOR
value is used, the output ripple voltage will increase Ceramic Taiyo Yuden (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 output capacitor value or add a 4.7pF feed-forward capaci- (803) 448-9411 tor in the feedback network of the LT1944-1 (see the www.avxcorp.com circuits in the Typical Applications section). Adding this Ceramic Murata small, inexpensive 4.7pF capacitor will greatly reduce the (714) 852-2001 www.murata.com output voltage ripple. 6
U U W U APPLICATIO S I FOR ATIO
limited to 100mA (or 175mA), the power switch of the
Setting the Output Voltage
LT1944-1 can handle larger currents without problem, but Set the output voltage for each switching regulator by the overall efficiency will suffer. Best results will be ob- choosing the appropriate values for feedback resistors R1 tained when IPEAK is kept below 400mA for the LT1944-1. and R2 (see Figure 1).
Capacitor Selection
V OUT Low ESR (Equivalent Series Resistance) capacitors should R1= R2 − 1 1 2 V 3 . be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are the best choice, as they have a very low ESR and are available in very small
Diode Selection
packages. Their small size makes them a good companion For most LT1944-1 applications, the Philips BAT54 or to the LT1944-1’s MS10 package. Solid tantalum capaci- Central Semiconductor CMDSH-3 surface mount Schottky tors (like the AVX TPS, Sprague 593D families) or OS-CON diodes are an ideal choice. Schottky diodes, with their low capacitors can be used, but they will occupy more board forward voltage drop and fast switching speed, are the area than a ceramic and will have a higher ESR. Always use best match for the LT1944-1. Many different manufactur- a capacitor with a sufficient voltage rating. ers make equivalent parts, but make sure that the compo- Ceramic capacitors also make a good choice for the input nent is rated to handle at least 100mA. decoupling capacitor, which should be placed as close as
Lowering Output Voltage Ripple
possible to the LT1944-1. A 4.7µF input capacitor is sufficient for most applications. Table 2 shows a list of Using low ESR capacitors will help minimize the output several capacitor manufacturers. Consult the manufactur- ripple voltage, but proper selection of the inductor and the ers for more detailed information and for their entire output capacitor also plays a big role. The LT1944-1 selection of related parts. provides energy to the load in bursts by ramping up the inductor current, then delivering that current to the load.
Table 2. Recommended Capacitors
If too large of an inductor value or too small of a capacitor
CAPACITOR TYPE VENDOR
value is used, the output ripple voltage will increase Ceramic Taiyo Yuden (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 output capacitor value or add a 4.7pF feed-forward capaci- (803) 448-9411 tor in the feedback network of the LT1944-1 (see the www.avxcorp.com circuits in the Typical Applications section). Adding this Ceramic Murata small, inexpensive 4.7pF capacitor will greatly reduce the (714) 852-2001 www.murata.com output voltage ripple. 6
