 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3853EUJ-PBF Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3853EUJ-PBF Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 36 page  LTC3853 11 3853f OPERATION Main Control Loop The LTC3853 is a constant-frequency, current mode step-down controller with three channels operating 120 degrees out-of-phase. During normal operation, each top MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the main current comparator, ICMP, resets the RS latch. The peak inductor current at which ICMP resets the RS latch is controlled by the voltage on the ITH pin, which is the output of each error amplifier, EA. The VFB pin receives the voltage feedback signal, which is compared to the internal reference voltage by the EA. When the load current increases, it causes a slight decrease in VFB relative to the 0.8V reference, which in turn causes the ITH voltage to increase until the average inductor current matches the new load current. After the top MOSFET has turned off, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the reverse current comparator IREV, or the beginning of the next cycle. INTVCC/EXTVCC/DRVCC12 Power Power for the top and bottom MOSFET drivers of phase 3 and most other internal circuitry is derived from the INTVCC pin. DRVCC12 provides driver power for phase 1 and phase 2. This pin must be externally tied to INTVCC. If EXTVCC is taken above 4.7V, the 5V regulator is turned off and an internal switch is turned on connecting EXTVCC. Using the EXTVCCpinallowstheINTVCCpowertobederived from a high efficiency external source such as one of the LTC3853 switching regulator outputs. Each top MOSFET driver is biased from the floating boot- strap capacitor, CB, which normally recharges during each off cycle through an external diode when the top MOSFET turns off. If the input voltage, VIN, decreases to a voltage close to VOUT, the loop may enter dropout and attempt to turn on the top MOSFET continuously. The dropout detec- tor detects this and forces the top MOSFET off for about one-twelfth of the clock period every fifth cycle to allow CB to recharge. However, it is recommended that there is always a load be present during the drop-out transition to ensure CB is recharged. Shutdown and Start-Up (RUN1, RUN2, RUN3 and TK/SS1, TK/SS2, TK/SS3 Pins) The three channels of the LTC3853 can be independently shut down using the RUN1, RUN2 and RUN3 pins. Pulling any of these pins below 1.2V shuts down the main control loop for that controller. Pulling all pins low disables all three controllers and most internal circuits, including the INTVCC regulator. Releasing any RUN pin allows an internal 0.5μA current to pull up the pin and enable that control- ler. Alternatively, the RUN pin may be externally pulled up or driven directly by logic. Be careful not to exceed the absolute maximum rating of 6V on this pin. The start-up of each controller’s output voltage VOUT is controlled by the voltage on the TK/SS1, TK/SS2 and TK/SS3 pins. When the voltage on the TK/SS pin is less than the 0.8V internal reference, the LTC3853 regulates the VFB voltage to the TK/SS pin voltage instead of the 0.8V reference. This allows the TK/SS pin to be used to program a soft-start by connecting an external capacitor from the TK/SS pin to SGND. An internal 1.3μA pull-up current charges this capacitor, creating a voltage ramp on the TK/SS pin. As the TK/SS voltage rises linearly from 0V to 0.8V (and beyond), the output voltage VOUT rises smoothly from zero to its final value. Alternatively the TK/SS pin can be used to cause the start-up of VOUT to “track” that of another supply. Typically, this requires connecting to the TK/SS pin an external resistor divider from the other supply to ground (see the Applications Information section). When the corresponding RUN pin is pulled low to disable a controller, or when INTVCC drops below its undervoltage lockout threshold of 3.35V, the TK/SS pin is pulled low by an internal MOSFET. When in undervoltage lockout, all controllers are disabled and the external MOSFETs are held off. Light Load Current Operation (Burst Mode Operation, Pulse Skipping or Continuous Conduction) The LTC3853 can be enabled to enter high efficiency Burst Mode operation, constant-frequency pulse skipping mode, or forced continuous conduction mode. To select forced continuous operation, tie the MODE/PLLIN pin to a DC |
Similar Part No. - LTC3853EUJ-PBF |
|
Similar Description - LTC3853EUJ-PBF |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
