Os motores de busca de Datasheet de Componentes eletrônicos |
|
LM3670MF-1.8 Folha de dados(PDF) 10 Page - National Semiconductor (TI) |
|
|
LM3670MF-1.8 Folha de dados(HTML) 10 Page - National Semiconductor (TI) |
10 / 17 page Typical Performance Characteristics (unless otherwise stated: V IN= 3.6V, VOUT= 1.8V) (Continued) Soft Start V IN,VOUT,IINDUCTOR vs. Time (I LOAD = 350mA) 20075824 Operation Description DEVICE INFORMATION The LM3670, a high efficiency step down DC-DC switching buck converter, delivers a constant voltage from either a single Li-Ion or three cell NiMH/NiCd battery to portable devices such as cell phones and PDAs. Using a voltage mode architecture with synchronous rectification, the LM3670 has the ability to deliver up to 350 mA depending on the input voltage and output voltage (voltage head room), and the inductor chosen (maximum current capability). There are three modes of operation depending on the cur- rent required - PWM (Pulse Width Modulation), PFM (Pulse Frequency Modulation), and shutdown. PWM mode handles current loads of approximately 70 mA or higher. Lighter output current loads cause the device to automatically switch into PFM for reduced current consumption (I Q = 15 µA typ) and a longer battery life. Shutdown mode turns off the de- vice, offering the lowest current consumption (I SHUTDOWN = 0.1 µA typ). The LM3670 can operate up to a 100% duty cycle (PMOS switch always on) for low drop out control of the output voltage. In this way the output voltage will be controlled down to the lowest possible input voltage. Additional features include soft-start, under voltage lock out, current overload protection, and thermal overload protection. As shown in Figure 1, only three external power components are required for implementation. CIRCUIT OPERATION The LM3670 operates as follows. During the first portion of each switching cycle, the control block in the LM3670 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 by storing energy in a magnetic field. During the second portion of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and then turns the NFET synchronous rectifier on. The inductor draws current from ground through the NFET to the output filter capacitor and load, which ramps the inductor current down with a slope of The output filter stores charge when the inductor current is high, and releases it when low, smoothing the voltage across the load. PWM OPERATION During PWM operation the converter operates as a voltage- mode controller with input voltage feed forward. This allows the converter to achieve excellent load and line regulation. The DC gain of the power stage is proportional to the input voltage. To eliminate this dependence, feed forward in- versely proportional to the input voltage is introduced. Internal Synchronous Rectification While in PWM mode, the LM3670 uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode. Current Limiting A current limit feature allows the LM3670 to protect itself and external components during overload conditions PWM mode implements cycle-by-cycle current limiting using an internal comparator that trips at 620 mA (typ). PFM OPERATION At very light load, the converter enters PFM mode and operates with reduced switching frequency and supply cur- rent to maintain high efficiency. www.national.com 10 |
Nº de peça semelhante - LM3670MF-1.8 |
|
Descrição semelhante - LM3670MF-1.8 |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes 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 |