Datasheet LT1316 (Analog Devices) - 9
| Hersteller | Analog Devices |
| Beschreibung | Micropower DC/DC Converter with Programmable Peak Current Limit |
| Seiten / Seite | 16 / 9 — APPLICATIONS INFORMATION. Diodes. Capacitor Selection. Lowering Output … |
| Dateiformat / Größe | PDF / 313 Kb |
| Dokumentensprache | Englisch |
APPLICATIONS INFORMATION. Diodes. Capacitor Selection. Lowering Output Ripple Voltage
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LT1316
U U W U APPLICATIONS INFORMATION
4. Find IPEAK for 3.4µs on-time For through-hole applications Sanyo OS-CON capacitors offer extremely low ESR in a small package size. If peak t 3.4µs(3.3 – 0.2) I ON(VIN – VSAT) switch current is reduced using the R PEAK = = SET pin, capacitor L 52µH requirements can be eased and smaller, higher ESR units = 0.202A can be used. Ordinary generic capacitors can generally be used when peak switch current is less than 100mA, 5. Find RSET resistor although output voltage ripple may increase. V Overshoot = IN 300ns ) )
Diodes
L Most of the application circuits on this data sheet specify 3.3 = 300ns = 19mA ) the Motorola MBR0520L surface mount Schottky diode. 52µH This 0.5A, low drop diode suits the LT1316 well. In lower current applications, a 1N4148 can be used although Find RSET from Figure 3 for 0.202A – 19mA = 0.183A efficiency will suffer due to the higher forward drop. This R effect is particularly noticeable at low output voltages. For SET ≈ 13k higher output voltage applications, such as LCD bias These discontinuous mode equations are designed to generators, the extra drop is a small percentage of the minimize peak current at the expense of inductor size. If output voltage so the efficiency penalty is small. The low smaller inductors are desired peak current must be cost of the 1N4148 makes it attractive wherever it can be increased. used. In through-hole applications the 1N5818 is the all around best choice.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
Lowering Output Ripple Voltage
be used at the output of the LT1316 to minimize output To obtain lower output ripple voltage, a small feedforward ripple voltage. High quality input bypassing is also capacitor of about 50pF to 100pF may be placed from required. For surface mount applications AVX TPS series VOUT to FB as detailed in Figure 6. Ripple voltages with tantalum capacitors are recommended. These have been and without the added capacitor are pictured in Figures specifically designed for switch mode power supplies and 7 and 8. have low ESR along with high surge current ratings. L1 SHUTDOWN 47µH D1 VOUT R1 + C1 1M 47µF V 100pF IN SW 1% SHDN FB + 2 LT1316 R2 47µF CELLS 324k 1% RSET GND 10k 1316 F06
Figure 6. 2-Cell to 5V Step-Up Converter with Reduced Output Ripple Voltage
9
U U W U APPLICATIONS INFORMATION
4. Find IPEAK for 3.4µs on-time For through-hole applications Sanyo OS-CON capacitors offer extremely low ESR in a small package size. If peak t 3.4µs(3.3 – 0.2) I ON(VIN – VSAT) switch current is reduced using the R PEAK = = SET pin, capacitor L 52µH requirements can be eased and smaller, higher ESR units = 0.202A can be used. Ordinary generic capacitors can generally be used when peak switch current is less than 100mA, 5. Find RSET resistor although output voltage ripple may increase. V Overshoot = IN 300ns ) )
Diodes
L Most of the application circuits on this data sheet specify 3.3 = 300ns = 19mA ) the Motorola MBR0520L surface mount Schottky diode. 52µH This 0.5A, low drop diode suits the LT1316 well. In lower current applications, a 1N4148 can be used although Find RSET from Figure 3 for 0.202A – 19mA = 0.183A efficiency will suffer due to the higher forward drop. This R effect is particularly noticeable at low output voltages. For SET ≈ 13k higher output voltage applications, such as LCD bias These discontinuous mode equations are designed to generators, the extra drop is a small percentage of the minimize peak current at the expense of inductor size. If output voltage so the efficiency penalty is small. The low smaller inductors are desired peak current must be cost of the 1N4148 makes it attractive wherever it can be increased. used. In through-hole applications the 1N5818 is the all around best choice.
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
Lowering Output Ripple Voltage
be used at the output of the LT1316 to minimize output To obtain lower output ripple voltage, a small feedforward ripple voltage. High quality input bypassing is also capacitor of about 50pF to 100pF may be placed from required. For surface mount applications AVX TPS series VOUT to FB as detailed in Figure 6. Ripple voltages with tantalum capacitors are recommended. These have been and without the added capacitor are pictured in Figures specifically designed for switch mode power supplies and 7 and 8. have low ESR along with high surge current ratings. L1 SHUTDOWN 47µH D1 VOUT R1 + C1 1M 47µF V 100pF IN SW 1% SHDN FB + 2 LT1316 R2 47µF CELLS 324k 1% RSET GND 10k 1316 F06
Figure 6. 2-Cell to 5V Step-Up Converter with Reduced Output Ripple Voltage
9