Datasheet LT1936 (Analog Devices) - 10
| 制造商 | Analog Devices |
| 描述 | 1.4A, 500kHz Step-Down Switching Regulator |
| 页数 / 页 | 20 / 10 — APPLICATIONS INFORMATION. Table 2. Capacitor Vendors. VENDOR. PHONE. URL. … |
| 文件格式/大小 | PDF / 306 Kb |
| 文件语言 | 英语 |
APPLICATIONS INFORMATION. Table 2. Capacitor Vendors. VENDOR. PHONE. URL. PART SERIES. COMMENTS. Frequency Compensation
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LT1936
APPLICATIONS INFORMATION Table 2. Capacitor Vendors VENDOR PHONE URL PART SERIES COMMENTS
Panasonic (714) 373-7366 www.panasonic.com Ceramic, Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum T494, T495 Sanyo (408) 749-9714 www.sanyovideo.com Ceramic, Polymer, POSCAP Tantalum Murata (404) 436-1300 www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden (864) 963-6300 www.taiyo-yuden.com Ceramic This is the minimum output capacitance required, not This capacitor (CF) is not part of the loop compensation the nominal capacitor value. For example, a 3.3V output but is used to fi lter noise at the switching frequency, and requires 20μF of output capacitance. If a small 22μF, 6.3V is required only if a phase-lead capacitor is used or if the ceramic capacitor is used, the circuit may be unstable be- output capacitor has high ESR. An alternative to using cause the effective capacitance is lower than the nominal external compensation components is to use the internal capacitance when biased at 3.3V. Look carefully at the RC network by tying the COMP pin to the VC pin. This re- capacitor’s data sheet to fi nd out what the actual capaci- duces component count but does not provide the optimum tance is under operating conditions (applied voltage and transient response when the output capacitor value is high, temperature). A physically larger capacitor, or one with a and the circuit may not be stable when the output capacitor higher voltage rating, may be required. value is low. If the internal compensation network is not used, tie COMP to ground or leave it fl oating. High performance electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one Loop compensation determines the stability and transient that is intended for use in switching regulators. The ESR performance. Designing the compensation network is a bit should be specifi ed by the supplier, and should be 0.05Ω or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the LT1936 capacitor must be large to achieve low ESR. Table 2 lists CURRENT MODE SW POWER STAGE OUTPUT several capacitor vendors. g ERROR m = 2mho AMPLIFIER R1 CPL – FB
Frequency Compensation
gm = 250μmho The LT1936 uses current mode control to regulate the + ESR 1.2V C1 + output. This simplifi es loop compensation. In particular, the 600k C1 LT1936 does not require the ESR of the output capacitor 150pF 50k POLYMER CERAMIC for stability, so you are free to use ceramic capacitors to OR VC COMP GND TANTALUM achieve low output ripple and small circuit size. R Frequency compensation is provided by the components CF C R2 tied to the V CC C pin, as shown in Figure 1. Generally a capaci- tor (CC) and a resistor (RC) in series to ground are used. 1936 F01 In addition, there may be lower value capacitor in parallel.
Figure 1. Model for Loop Response
1936fd 10
APPLICATIONS INFORMATION Table 2. Capacitor Vendors VENDOR PHONE URL PART SERIES COMMENTS
Panasonic (714) 373-7366 www.panasonic.com Ceramic, Polymer, EEF Series Tantalum Kemet (864) 963-6300 www.kemet.com Ceramic, Tantalum T494, T495 Sanyo (408) 749-9714 www.sanyovideo.com Ceramic, Polymer, POSCAP Tantalum Murata (404) 436-1300 www.murata.com Ceramic AVX www.avxcorp.com Ceramic, Tantalum TPS Series Taiyo Yuden (864) 963-6300 www.taiyo-yuden.com Ceramic This is the minimum output capacitance required, not This capacitor (CF) is not part of the loop compensation the nominal capacitor value. For example, a 3.3V output but is used to fi lter noise at the switching frequency, and requires 20μF of output capacitance. If a small 22μF, 6.3V is required only if a phase-lead capacitor is used or if the ceramic capacitor is used, the circuit may be unstable be- output capacitor has high ESR. An alternative to using cause the effective capacitance is lower than the nominal external compensation components is to use the internal capacitance when biased at 3.3V. Look carefully at the RC network by tying the COMP pin to the VC pin. This re- capacitor’s data sheet to fi nd out what the actual capaci- duces component count but does not provide the optimum tance is under operating conditions (applied voltage and transient response when the output capacitor value is high, temperature). A physically larger capacitor, or one with a and the circuit may not be stable when the output capacitor higher voltage rating, may be required. value is low. If the internal compensation network is not used, tie COMP to ground or leave it fl oating. High performance electrolytic capacitors can be used for the output capacitor. Low ESR is important, so choose one Loop compensation determines the stability and transient that is intended for use in switching regulators. The ESR performance. Designing the compensation network is a bit should be specifi ed by the supplier, and should be 0.05Ω or less. Such a capacitor will be larger than a ceramic capacitor and will have a larger capacitance, because the LT1936 capacitor must be large to achieve low ESR. Table 2 lists CURRENT MODE SW POWER STAGE OUTPUT several capacitor vendors. g ERROR m = 2mho AMPLIFIER R1 CPL – FB
Frequency Compensation
gm = 250μmho The LT1936 uses current mode control to regulate the + ESR 1.2V C1 + output. This simplifi es loop compensation. In particular, the 600k C1 LT1936 does not require the ESR of the output capacitor 150pF 50k POLYMER CERAMIC for stability, so you are free to use ceramic capacitors to OR VC COMP GND TANTALUM achieve low output ripple and small circuit size. R Frequency compensation is provided by the components CF C R2 tied to the V CC C pin, as shown in Figure 1. Generally a capaci- tor (CC) and a resistor (RC) in series to ground are used. 1936 F01 In addition, there may be lower value capacitor in parallel.
Figure 1. Model for Loop Response
1936fd 10