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LM27222SD Arkusz danych(PDF) 8 Page - Texas Instruments |
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LM27222SD Arkusz danych(HTML) 8 Page - Texas Instruments |
8 / 16 page GND OUT1 CMP1 CMPREF CMP2 VREF VDD U1 Q1 Q2 L1 R8 Q3 Q4 L2 R9 D1 C4 D2 C5 + C6 + C7 R5 R4 VCC5 VIN U2 LM27222 U3 LM27222 C3 C2 R6 R7 SYNC1 SYNC2 OUT2 C1 R1 R2 R3 VCC LEN IN GND CB HG SW LG VCC LEN IN GND CB HG SW LG 10: 0.1 PF 1.5: 1.5: 121: 121: 60.4: 60.4: 1 PF, 6.3V 1 PF, 6.3V 0.33 PF ** 0.6 PH 30A 1 m: 270 PF x 3 ESR = 9 m: /cap VOUT VIN * 0.6 PH 30A * ** 0.33 PF 10 PF x 6 1 m: LM27222 SNVS306B – SEPTEMBER 2004 – REVISED MARCH 2013 www.ti.com TYPICAL APPLICATION CIRCUIT DESCRIPITON The Application Example on the following page shows the LM27222 being used with the LM27212, a 2-phase hysteretic current mode controller. Although this circuit is capable of operating from 5V to 28V, the components are optimized for an input voltage range of 9V to 28V. The high-side FET is selected for low gate charge to reduce switching losses. For low duty cycles, the average current through the high-side FET is relatively small and thus we trade off higher conduction losses for lower switching losses. The low-side FET is selected solely on RDS_ON to minimize conduction losses. If the input voltage range were 4V to 6V, the MOSFET selection should be changed. First, much lower voltage FETs can be used, and secondly, high-side FET RDS_ON becomes a larger loss factor than the switching losses. Of course with a lower input voltage, the input capacitor voltage rating can be reduced and the inductor value can be reduced as well. For a 4V to 6V application, the inductor can be reduced to 200nH to 300nH. The switching frequency of the LM27212 is determined by the allowed ripple current in the inductor. This circuit is set for approximately 300kHz. At lower input voltages, higher frequencies are possible without suffering a significant efficiency loss. Although the LM27222 can support operating frequencies up to 2MHz in many applications, the LM27212 should be limited to about 1MHz. The control architecture of the LM27212 and the low propagation times of the LM27222 potentially gives this solution the fastest transient response in the industry. Application Example * Q1, Q3: 2 x Si7390DP ** Q2, Q4: 2 x Si7356DP 8 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Product Folder Links: LM27222 |
Podobny numer części - LM27222SD |
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Podobny opis - LM27222SD |
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