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LM2612BBLX bảng dữ liệu(PDF) 11 Page - National Semiconductor (TI) |
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LM2612BBLX bảng dữ liệu(HTML) 11 Page - National Semiconductor (TI) |
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11 / 19 page  Device Information The LM2612 is a simple, step-down DC-DC converter opti- mized for powering low-voltage CPUs or DSPs in cell phones and other miniature battery powered devices. It pro- vides pin-selectable output voltages of 1.05V, 1.3V, 1.5V or 1.8V from a single 2.8V to 5.5V LiION battery cell. It is designed for a maximum load current of 400mA (300mA for B grade). The device has all three of the pin-selectable operating modes required for cell phones and other complex portable devices. Such applications typically spend a small portion of their time operating at full power. During full power operation, synchronized or fixed-frequency PWM mode offers full out- put current capability while minimizing interference to sensi- tive IF and data acquisition circuits. PWM mode uses syn- chronous rectification for high efficiency: typically 91% for a 100mA load with 1.8V output, 2.8V input. These applications spend the remainder of their time in low-current standby operation or shutdown to conserve battery power. During standby operation, hysteretic PFM mode reduces quiescent current to 160µA typ to maximize battery life. Shutdown mode turns the device off and reduces battery consumption to 0.02µA (typ.). The LM2612 offers good performance and a full set of fea- tures. It is based on a current-mode switching buck architecture. The SYNC/MODE input accepts an external clock between 500kHz and 1MHz. The output voltage selec- tion pins eliminate external feedback resistors. Additional features include soft-start, current overload protection, over- voltage protection and thermal shutdown protection. The LM2612 is constructed using a chip-scale 10-pin micro SMD package. The micro SMD package offers the smallest possible size for space critical applications, such as cell phones. Required external components are only a small 10uH inductor, and tiny 10uF and 22uF ceramic capacitors for reduced board area. Circuit Operation Referring to Figure 1, Figure 2, and Figure 3 the LM2612 operates as follows: During the first part of each switching cycle, the control block in the LM2612 turns on the internal PFET switch. This allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor limits the current to a ramp with a slope of (V IN -V OUT)/L, by storing energy in a magnetic field. During the second part of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and then turns the NFET synchronous rectifier on. In response, the inductor’s magnetic field collapses, generating a voltage that forces current from ground through the synchronous rectifier to the output filter capacitor and load. As the stored energy is transferred back into the circuit and depleted, the inductor current ramps down with a slope of V OUT/L. If the inductor current reaches zero before the next cycle, the synchronous rectifier is turned off to prevent current reversal. The output filter capacitor stores charge when the inductor current is high, and releases it when low, smoothing the voltage across the load. The output voltage is regulated by modulating the PFET switch on-time to control the average current sent to the load. The effect is identical to sending a duty-cycle modu- lated rectangular wave formed by the switch and synchro- nous rectifier to a low-pass filter created by the inductor and output filter capacitor. The output voltage is equal to the average voltage at the SW pin. 20041803 FIGURE 1. Typical Operating Circuit www.national.com 11 |
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Mô tả tương tự - LM2612BBLX |
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