công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
|
LM3200 bảng dữ liệu(PDF) 11 Page - National Semiconductor (TI) |
|
|
LM3200 bảng dữ liệu(HTML) 11 Page - National Semiconductor (TI) |
11 / 15 page Operation Description (Continued) sophisticated portable device with complex power manage- ment needs. Fixed-frequency PWM operation offers regu- lated output at high efficiency while minimizing interference with sensitive IF and data acquisition circuits. Bypass mode (Forced or Automatic) turns on an internal FET bypass switch to power the PA directly from the battery. Shutdown mode turns the device off and reduces battery consumption to 0.1 µA (typ). DC PWM mode output voltage precision is +/-2% for 3.6V OUT. Efficiency is typically around 96% for a 120 mA load with 3.2V output, 3.6V input. PWM mode quiescent current is 0.7 mA typ. The output voltage is dynamically programmable from 0.8V to 3.6V by adjusting the voltage on the control pin without the need for external feedback resis- tors. This ensures longer battery life by being able to change the PA supply voltage dynamically depending on its trans- mitting power. Additional features include current overload protection, over voltage protection and thermal shutdown. The LM3200 is constructed using a chip-scale 10-pin micro SMD package. This package offers the smallest possible size, for space-critical applications such as cell phones, where board area is an important design consideration. Use of a high switching frequency (2 MHz) reduces the size of external components. As shown in Figure 1, only few exter- nal components are required for implementation. Use of a micro SMD package requires special design considerations for implementation. (See Micro SMD Package Assembly and use in the Applications Information section.) Its fine bump- pitch requires careful board design and precision assembly equipment. Use of this package is best suited for opaque- case applications, where its edges are not subject to high- intensity ambient red or infrared light. Also, the system con- troller should set EN low during power-up and other low supply voltage conditions. (See Shutdown Mode in the De- vice Information section.) Circuit Operation Referring to Figure 1, the LM3200 operates as follows. Dur- ing the first part of each switching cycle, the control block in the LM3200 turns on the internal PFET (P-channel MOS- FET) 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 around (V IN-VOUT)/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 (N-channel MOSFET) synchronous rectifier on. In response, the inductor’s magnetic field col- lapses, 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 around V OUT/L. The output filter capacitor stores charge when the inductor current is going high, and releases it when inductor current is going 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 modulated rectangular wave formed by the switch and synchronous rectifier at SW to a low-pass filter formed by the inductor and output filter capacitor. The output voltage is equal to the average voltage at the SW pin. PWM Mode While in PWM (Pulse Width Modulation) mode, the output voltage is regulated by switching at a constant frequency and then modulating the energy per cycle to control power to the load. Energy per cycle is set by modulating the PFET switch on-time pulse width to control the peak inductor cur- rent. This is done by comparing the signal from the PFET drain current to a slope-compensated reference current gen- erated by the error amplifier. At the beginning of each cycle, the clock turns on the PFET switch, causing the inductor current to ramp up. When the current sense signal ramps past the error amplifier signal, the PWM comparator turns off the PFET switch and turns on the NFET synchronous recti- fier, ending the first part of the cycle. If an increase in load pulls the output down, the error amplifier output increases, which allows the inductor current to ramp higher before the comparator turns off the PFET. This increases the average current sent to the output and adjusts for the increase in the load. Before appearing at the PWM comparator, a slope 20126136 FIGURE 1. Typical Operating System Circuit www.national.com 11 |
Số phần tương tự - LM3200 |
|
Mô tả tương tự - LM3200 |
|
|
Link URL |
Chính sách bảo mật |
ALLDATASHEET.VN |
Cho đến nay ALLDATASHEET có giúp ích cho doanh nghiệp của bạn hay không? [ DONATE ] |
Alldatasheet là | Quảng cáo | Liên lạc với chúng tôi | Chính sách bảo mật | Trao đổi link | Tìm kiếm theo nhà sản xuất All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |