 |
Datenblatt-Suchmaschine für elektronische Bauteile |
|
|
Datenblatt-Suchmaschine für elektronische Bauteile |
|
LM3671MFX-1.25 Datenblatt(PDF) 11 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM3671MFX-1.25 Datenblatt(HTML) 11 Page - National Semiconductor (TI) |
|
|
11 / 16 page  Operation Description (Continued) During PFM operation, the converter positions the output voltage slightly higher than the nominal output voltage during PWM operation, allowing additional headroom for voltage drop during a load transient from light to heavy load. The PFM comparators sense the output voltage via the feedback pin and control the switching of the output FETs such that the output voltage ramps between ~0.6% and ~1.7% above the nominal PWM output voltage. If the output voltage is below the ‘high’ PFM comparator threshold, the PMOS power switch is turned on. It remains on until the output voltage reaches the ‘high’ PFM threshold or the peak current ex- ceeds the I PFM level set for PFM mode. The typical peak current in PFM mode is: I PFM = 112mA + VIN/27 Ω . Once the PMOS power switch is turned off, the NMOS power switch is turned on until the inductor current ramps to zero. When the NMOS zero-current condition is detected, the NMOS power switch is turned off. If the output voltage is below the ‘high’ PFM comparator threshold (see Figure 7), the PMOS switch is again turned on and the cycle is re- peated until the output reaches the desired level. Once the output reaches the ‘high’ PFM threshold, the NMOS switch is turned on briefly to ramp the inductor current to zero and then both output switches are turned off and the part enters an extremely low power mode. Quiescent supply current during this ‘sleep’ mode is 16µA (typ), which allows the part to achieve high efficiencies under extremely light load con- ditions. When the output drops below the ‘low’ PFM thresh- old, the cycle repeats to restore the output voltage (average voltage in pfm mode) to ∼1.15% above the nominal PWM output voltage. If the load current should increase during PFM mode (see Figure 7) causing the output voltage to fall below the ‘low2’ PFM threshold, the part will automatically transition into fixed-frequency PWM mode. When V IN =2.8V the part tran- sitions from PWM to PFM mode at ~35mA output current and from PFM to PWM mode at ~85mA , when V IN=3.6V, PWM to PFM transition happens at ~50mA and PFM to PWM transition happens at ~100mA, when V IN =4.5V, PWM to PFM transition happens at ~65mA and PFM to PWM transition happens at ~115mA. SHUTDOWN MODE Setting the EN input pin low (<0.4V) places the LM3671 in shutdown mode. During shutdown the PFET switch, NFET switch, reference, control and bias circuitry of the LM3671 are turned off. Setting EN high (>1.0V) enables normal operation. While turning on the device with EN, soft start is activated. It is recommended to set EN pin low to turn off the LM3671 during system power up and undervoltage condi- 20108422 FIGURE 6. Typical PFM Operation 20108403 FIGURE 7. Operation in PFM Mode and Transfer to PWM Mode www.national.com 11 |
Ähnliche Teilenummer - LM3671MFX-1.25 |
|
Ähnliche Beschreibung - LM3671MFX-1.25 |
|
|
|
Link URL |
| Privatsphäre und Datenschutz |
| ALLDATASHEETDE.COM |
| War ALLDATASHEET hilfreich? [ DONATE ] |
Über Alldatasheet | Werbung | Kontakt | Privatsphäre und Datenschutz | Linktausch | Hersteller 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 |
German ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
