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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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LTC3124 датащи(PDF) 20 Page - Linear Technology |
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LTC3124 датащи(HTML) 20 Page - Linear Technology |
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20 / 28 page  LTC3124 20 3124f For more information www.linear.com/LTC3124 APPLICATIONS INFORMATION Decide how much phase margin ( Φm) is desired. Greater phasemargincanoffermorestabilitywhilelowerphasemar- gin can yield faster transient response. Typically, Φm≈60° is optimal for minimizing transient response time while allowing sufficient margin to account for component variability. Φ1 is the phase boost of Z1, P2, and P5 while Φ2 is the phase boost of Z4 and P4. Select Φ1 and Φ2 such that: Φ1 + Φ2 = Φm + tan− 1 ƒC Z3 and Φ1 ≤ 74°; Φ2 ≤ 2 • tan−1 VOUT 1.2V − 90° where VOUT is in V and ƒC and Z3 are in kHz. Setting Z1, P5, Z4, and P4 such that Z1 = ƒC a1 , P5 = ƒC a1, Z4 = ƒC a2 , P4 = ƒC a2 allows a1 and a2 to be determined using Φ1 and Φ2 a1 = tan2 Φ1 + 90° 2 , a2 = tan2 Φ2 +90° 2 The compensation will force the converter gain GBOOST to unity at ƒC by using the following expression for CC: CC = 103 • gma •R2 •GƒC a1 − 1 ( ) a2 2 π • ƒC • R1+R2 ( ) a1 pF (gma in µS, ƒC in kHz, GƒC in V/V) Once CC is calculated, RC and CF are determined by: RC = 106 • a1 2 π • ƒC •CC k Ω (ƒC in kHz, CC in pF) CF = CC a1 − 1 Amethodforimprovingtheconverter’stransientresponse uses a small feedforward series network of a capacitor and a resistor across the top resistor of the feedback divider (from VOUT to FB). This adds a phase-lead zero and pole to the transfer function of the converter. The values of these phase lead components are given by the expressions: RPL = R1 − a2 • R1•R2 R1 +R2 a2 − 1 k Ω and CPL = 106 a2 − 1 ( ) R1+R2 ( ) 2 π • ƒC •R1 2 a2 pF where R1, R2, and RPL are in kΩ and ƒC is in kHz. Note that selecting Φ2 = 0° forces a2 = 1, and so the converter will have Type II compensation and therefore no feedforward: RPL is open (infinite impedance) and CPL = 0pF. If a2 = 0.833 • VOUT (its maximum), feedforward is maximized; RPL = 0 and CPL is maximized for this com- pensation method. Once the compensation values have been calculated, ob- taining a converter bode plot is strongly recommended to verify calculations and adjust values as required. Using the circuit in Figure 8 as an example, Table 4 shows the parameters used to generate the Bode plot shown in Figure 9. Table 4. Bode Plot Parameters PARAMETER VALUE UNITS COMMENT VIN 5 V App Specific VOUT 12 V App Specific RL 8 Ω App Specific COUT at No Bias COUT at 12V Bias 22 × 2 14 × 2 µF µF App Specific App Specific RESR 2.5 mΩ App Specific LA, LB 4.7 µH App Specific fSWITCH 1 MHz Adjustable R1 1020 kΩ Adjustable R2 113 kΩ Adjustable gma 100 µS Fixed RO 10 MΩ Fixed gmp 3.4 S Fixed η 90 % App Specific RC 84.5 kΩ Adjustable CC 680 pF Adjustable CF 56 pF Adjustable RPL Open kΩ Optional CPL 0 pF Optional |
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