LT3580I 데이터 시트보기 (PDF) - Linear Technology

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LT3580I

Boost/Inverting DC/DC Converter with 2A Switch, Soft-Start, and Synchronization

Linear Technology 

LT3580

APPLICATIONS INFORMATION

these materials retain their capacitance over wider voltage

and temperature ranges. A 4.7μF to 20μF output capaci-

tor is sufficient for most applications, but systems with

very low output currents may need only a 1μF or 2.2μF

output capacitor. Always use a capacitor with a sufficient

voltage rating. Many capacitors rated at 2.2μF to 20μF,

particularly 0805 or 0603 case sizes, have greatly reduced

capacitance at the desired output voltage. Solid tantalum

or OS-CON capacitors can be used, but they will occupy

more board area than a ceramic and will have a higher

ESR with greater output ripple.

Ceramic capacitors also make a good choice for the input

decoupling capacitor, which should be placed as closely as

possible to the LT3580. A 2.2μF to 4.7μF input capacitor

is sufficient for most applications.

Table 2 shows a list of several ceramic capacitor manufac-

turers. Consult the manufacturers for detailed information

on their entire selection of ceramic parts.

Table 2. Ceramic Capacitor Manufacturers

Kemet

www.kemet.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

Compensation—Adjustment

To compensate the feedback loop of the LT3580, a series

resistor-capacitor network in parallel with a single capacitor

should be connected from the VC pin to GND. For most

applications, the series capacitor should be in the range

of 470pF to 2.2nF with 1nF being a good starting value.

The parallel capacitor should range in value from 10pF to

100pF with 47pF a good starting value. The compensation

resistor, RC, is usually in the range of 5k to 50k. A good

technique to compensate a new application is to use a

100kΩ potentiometer in place of series resistor RC. With

the series capacitor and parallel capacitor at 1nF and 47pF

respectively, adjust the potentiometer while observing the

transient response and the optimum value for RC can be

found. Figures 3a to 3c illustrate this process for the circuit

of Figure 14 with a load current stepped between 400mA

and 500mA. Figure 3a shows the transient response with

RC equal to 1k. The phase margin is poor, as evidenced by

the excessive ringing in the output voltage and inductor

current. In Figure 3b, the value of RC is increased to 3k,

which results in a more damped response. Figure 3c

shows the results when RC is increased further to 10k. The

transient response is nicely damped and the compensation

procedure is complete.

VOUT

200mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 1k

200μs/DIV

3580 F03a

Figure 3a. Transient Response Shows Excessive Ringing

VOUT

200mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 3k

200μs/DIV

3580 F03b

Figure 3b. Transient Response Is Better

10

VOUT

200mV/DIV

AC COUPLED

IL

0.5A/DIV

RC = 10k

200μs/DIV

3580 F03c

Figure 3c. Transient Response Is Well Damped

3580fg

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