Datasheet LT3487 (Analog Devices) - 9
| Fabricante | Analog Devices |
| Descripción | Boost and Inverting Switching Regulator for CCD Bias |
| Páginas / Página | 16 / 9 — APPLICATIO S I FOR ATIO. Table 2. Recommended Ceramic Capacitor … |
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APPLICATIO S I FOR ATIO. Table 2. Recommended Ceramic Capacitor Manufacturers. MANUFACTURER. PHONE. URL. Inrush Current
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LT3487
U U W U APPLICATIO S I FOR ATIO Table 2. Recommended Ceramic Capacitor Manufacturers
where L is the inductance, r is the resistance of the inductor
MANUFACTURER PHONE URL
and C is the output capacitance. For low DCR inductors, Taiyo Yuden (408) 573-4150 www.t-yuden.com which is usually the case for this application, the peak Murata (814) 237-1431 www.murata.com inrush current can be simplifi ed as follows: Kemet (408) 986-0424 www.kemet.com ⎛ α π⎞ – •
Inrush Current
V – . 0 6 I IN = • e⎝⎜ ω 2 ⎠⎟ P L • ω The LT3487 uses internal Schottky diodes. When a sup- ply voltage is abruptly applied to the V Table 3 gives inrush peak currents for some component IN pin, the voltage difference between V selections. Note that inrush current is not a concern if the IN and VCAP generates inrush current fl owing from the input through the inductor L1 and the input voltage rises slowly. internal Schottky diode DP to charge the boost output
Table 3. Inrush Peak Current
capacitor C4. For the inverting channel, there is a similar
VIN (V) R (
Ω
) L (μH) C (μF) IP (A)
inrush current fl owing from the input through the inductor 5 0.18 10 4.7 1.44 L2 path, charging the fl ying capacitor C2 and returning 5 0.235 15 2.2 1.06 through the internal Schottky diode DN. The maximum 3.6 0.18 10 4.7 0.979 current the Schottky diodes in the LT3487 can sustain is 3.6 0.245 10 4.7 0.958 2A. The selection of inductor and capacitor values should 3.6 0.345 15 2.2 0.704 ensure that the peak inrush current is below 2A. The peak inrush current can be calculated as follows:
External Diode Selection
α ⎛ ω ⎞ As stated previously, the LT3487 has internal Schottky V – . – •arctan 0 6 ⎡ ⎛ ω ⎞ ⎤ diodes. The Schottky diode, DP, is suffi cient for most I IN = • e ω ⎝⎜ α ⎠⎟ • SIN P arctan ⎢ ⎥ L • ω ⎝⎜ ⎣ α ⎠⎟ ⎦ step-up applications. However, for high current inverter applications, a properly selected external Schottky diode in r + α = 1.5 parallel with DN can improve effi ciency. For external diode 2 • L selection, both forward voltage drop and diode capacitance ω = 1 r need to be considered. Schottky diodes rated for higher – L • C 4 • L2 current usually have lower forward voltage drops and larger capacitance, which can cause signifi cant switching losses at a 2MHz switching frequency. Some recommended Schottky diodes are listed in Table 4.
Table 4. Recommended Schottky Diodes DIODE CAPACITANCE PART NUMBER FORWARD CURRENT (mA) FORWARD VOLTAGE DROP (V) (pF at 10V) MANUFACTURER
PMEG2010AEB 1000 0.51 7.5 Philips www.semiconductors. philips.com CMDSH2-3 200 0.49 15 Central Semiconductor www.centralsemi.com RSX051VA-30 500 0.35 30 ROHM www.rohm.com ZHCS400 400 0.425 18 Zetex www.zetex.com 3487f 9
U U W U APPLICATIO S I FOR ATIO Table 2. Recommended Ceramic Capacitor Manufacturers
where L is the inductance, r is the resistance of the inductor
MANUFACTURER PHONE URL
and C is the output capacitance. For low DCR inductors, Taiyo Yuden (408) 573-4150 www.t-yuden.com which is usually the case for this application, the peak Murata (814) 237-1431 www.murata.com inrush current can be simplifi ed as follows: Kemet (408) 986-0424 www.kemet.com ⎛ α π⎞ – •
Inrush Current
V – . 0 6 I IN = • e⎝⎜ ω 2 ⎠⎟ P L • ω The LT3487 uses internal Schottky diodes. When a sup- ply voltage is abruptly applied to the V Table 3 gives inrush peak currents for some component IN pin, the voltage difference between V selections. Note that inrush current is not a concern if the IN and VCAP generates inrush current fl owing from the input through the inductor L1 and the input voltage rises slowly. internal Schottky diode DP to charge the boost output
Table 3. Inrush Peak Current
capacitor C4. For the inverting channel, there is a similar
VIN (V) R (
Ω
) L (μH) C (μF) IP (A)
inrush current fl owing from the input through the inductor 5 0.18 10 4.7 1.44 L2 path, charging the fl ying capacitor C2 and returning 5 0.235 15 2.2 1.06 through the internal Schottky diode DN. The maximum 3.6 0.18 10 4.7 0.979 current the Schottky diodes in the LT3487 can sustain is 3.6 0.245 10 4.7 0.958 2A. The selection of inductor and capacitor values should 3.6 0.345 15 2.2 0.704 ensure that the peak inrush current is below 2A. The peak inrush current can be calculated as follows:
External Diode Selection
α ⎛ ω ⎞ As stated previously, the LT3487 has internal Schottky V – . – •arctan 0 6 ⎡ ⎛ ω ⎞ ⎤ diodes. The Schottky diode, DP, is suffi cient for most I IN = • e ω ⎝⎜ α ⎠⎟ • SIN P arctan ⎢ ⎥ L • ω ⎝⎜ ⎣ α ⎠⎟ ⎦ step-up applications. However, for high current inverter applications, a properly selected external Schottky diode in r + α = 1.5 parallel with DN can improve effi ciency. For external diode 2 • L selection, both forward voltage drop and diode capacitance ω = 1 r need to be considered. Schottky diodes rated for higher – L • C 4 • L2 current usually have lower forward voltage drops and larger capacitance, which can cause signifi cant switching losses at a 2MHz switching frequency. Some recommended Schottky diodes are listed in Table 4.
Table 4. Recommended Schottky Diodes DIODE CAPACITANCE PART NUMBER FORWARD CURRENT (mA) FORWARD VOLTAGE DROP (V) (pF at 10V) MANUFACTURER
PMEG2010AEB 1000 0.51 7.5 Philips www.semiconductors. philips.com CMDSH2-3 200 0.49 15 Central Semiconductor www.centralsemi.com RSX051VA-30 500 0.35 30 ROHM www.rohm.com ZHCS400 400 0.425 18 Zetex www.zetex.com 3487f 9