AN1126 STMICROELECTRONICS | Alldatasheet

Document overview

  • Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
  • PDF pages: 16

Technical content

3.3V are also possible (See Application Note AN938). the efficiency is 87%. At 3.5A output, the efficiency is 90%. vice in the L497x family can be used for this purpose. The U1 regulator acts as a master which regulates the output voltage. Figure 1. Current Sharing Operating Principle

result the output current delivered to the load is Iout = 2I- = 2I+ for every load condition. chosen as a compromise between error minimization and system efficiency. (LM358A), the maximum relative percentage error is 1.7% (120mA @ Iout = 7A). and connected to the output ground point. tors and the two SYNC pins are connected. Figure 2. Layout hints.

reducing of the capacitor cost and size. Minimization of ripple current through the output capacitor and ground path. Fast load transient response. Minimization of the RMS Current Through the Input Capacitor. ripple current through the coil of 0.1⋅ Iout. allows a savings of 1.23W which corresponds to the 3.5% of the power delivered to the load. Figure 5. RMS current through the input capacitor for a different phase delay, α , with a duty

with Iout = 7A, there is in both cases a ΔP% gain of 3% . Table1 shows in details the major tips for different output voltages. Table 1. Vcc = 12V , Iout = 7A, ESR=100mΩ . The gained power ΔP% versus duty cycle is shown in figure 10. Figure 10. Power saved vs. Iout.

Table 2. Output voltage selection Main Components Description. tor for each of the two sections. the maximum RMS input current. maximum and is given by Io/2 . So the RMS current to be sustained is 3.5A. The two selected capacitor, FA 680µF/50V Panasonic, are able to support this current. where Vf is the freewheeling diode forward voltage. The inductor ripple current is fixed at 15% of Iomax and it is 0.525A. wire 34 turns, which correspond to 84µH of inductance at light load. Figure 16. Board efficiency vs. output current.

With this choice the core losses are approximately 280mW. The temperature increasing of the core is 12°C approximately. Output Capacitor The selection of Cout is driven by the output ripple voltage required, 1% of Vo. This is defined by the ESR of the output capacitance and by the maximum ripple current (0.525A). The maximum ESR is: ESR = ΔVo/ΔIo = 0.051/0.525 = 97mΩ The selected capacitance is 220µF/35V FA Panasonic with ESR = 90mW and the ripple voltage is 0.92% of Vo (47mV). Bill of Material C1, C3 680 µF / 35V FA PANASONIC 16x15 Irms=1690mA C2 1.2nF/35V SMD 1206 C4 22nF SMD 1206 C16 4.7nF SMD 1206 C13 100nF/35V SMD 1206 C5,C15 15nF/35V SMD 1206 C6,C7,C12,C17,C18,C23 220nF/50V SMD 10% Kemet 1206 X7R C8,C21 220 µF/35V FA PANASONIC 8x15 C10,C20 1 µF/10V electrolitic (not SMD) C11,C22 not used C14 10nF/35V SMD 1206 C9,C19 220pF SMD 1206 U1,U2 L4973D3.3 R1 22k SMD 1% 1206, 0.25W R2 9.1k SMD 1% 1206, 0.25W R3,R10 2.7k SMD 1% 1206, 0.25W R4,R12 4.7k SMD 1% 1206, 0.25W R6,R9 0.025 Ohm 1W 1% DALE WSL-2512 R7 0 SMD 1206 R11,R5,R8 10K SMD 1% 1206, 0.25W D1 STPS640CB (DPAK) D2 STPS640CB (DPAK) U3 LM358 SO8 ST Z1 Diodo Zener 25V SOT23 L1,L2 43 µH KoolMu Magnetics core 77120 34 Turns d(mm)=0.91 AWG19 Stability Analysis of the Current Loop. In the current sharing configuration the U1 regulator acts as a master in order to regulate the output voltage. The second section U2 works as current follower. Its task is to deliver an output current equal to the current delivered from the first section. For the analysis of the stability, see Fig. 21, the current loop of the U2 section can be considered as a separated loop from the voltage loop of the U1 section, consid- ering that the current loop is quite faster than the voltage one. AN1126 APPLICATION NOTE

Figure 25. PCB Layout top view: Silk, component side and bottom layer (1:1.25 scale).

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics © 1999 STMicroelectronics – Printed in Italy – All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. http://www.st.com AN1126 APPLICATION NOTE