 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3780IG Datasheet(PDF) 13 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3780IG Datasheet(HTML) 13 Page - Linear Technology |
|
|
13 / 30 page  LTC3780 13 3780ff For more information www.linear.com/LTC3780 operaTion MAIN CONTROL LOOP The LTC3780 is a current mode controller that provides an output voltage above, equal to or below the input voltage. The LTC proprietary topology and control architecture em- ploys a current-sensing resistor in buck or boost modes. The sensed inductor current is controlled by the voltage on the ITH pin, which is the output of the amplifier EA. The VOSENSE pin receives the voltage feedback signal, which is compared to the internal reference voltage by the EA. The top MOSFET drivers are biased from floating boost- strap capacitors CAandCB(Figure11),whicharenormally rechargedthroughanexternaldiodewhenthetopMOSFET is turned off. Schottky diodes across the synchronous switch D and synchronous switch B are not required, but provide a lower drop during the dead time. The addition of the Schottky diodes will typically improve peak efficiency by 1% to 2% at 400kHz. The main control loop is shut down by pulling the RUN pin low. When the RUN pin voltage is higher than 1.5V, an internal 1.2µA current source charges soft-start capacitor CSS at the SS pin. The ITH voltage is then clamped to the SS voltage while CSS is slowly charged during start-up. This “soft-start” clamping prevents abrupt current from being drawn from the input power supply. POWER SWITCH CONTROL Figure 1 shows a simplified diagram of how the four power switches are connected to the inductor, VIN, VOUT and GND. Figure 2 shows the regions of operation for the LTC3780 as a function of duty cycle D. The power switches are properly controlled so the transfer between modes is continuous. When VIN approaches VOUT, the buck-boost region is reached; the mode-to-mode transition time is typically 200ns. Buck Region (VIN > VOUT) Switch D is always on and switch C is always off during this mode. At the start of every cycle, synchronous switch B is turned on first. Inductor current is sensed when synchronous switch B is turned on. After the sensed in- ductor current falls below the reference voltage, which is proportional to VITH, synchronous switch B is turned off and switch A is turned on for the remainder of the cycle. switches A and B will alternate, behaving like a typical synchronous buck regulator. The duty cycle of switch A increases until the maximum duty cycle of the converter in buck mode reaches DMAX_BUCK, given by: DMAX_BUCK = 100% – DBUCK-BOOST where DBUCK-BOOST = duty cycle of the buck-boost switch range: DBUCK-BOOST = (200ns • f) • 100% and f is the operating frequency in Hz. Figure 3 shows typical buck mode waveforms. If VIN approaches VOUT, the buck-boost region is reached. Buck-Boost (VIN @ VOUT) When VIN is close to VOUT, the controller is in buck-boost mode. Figure 4 shows typical waveforms in this mode. Every cycle, if the controller starts with switches B and D turned on, switches A and C are then turned on. Finally, switches A and D are turned on for the remainder of the time. If the controller starts with switches A and C turned TG2 BG2 TG1 BG1 RSENSE 3780 F01 A B D C L SW2 SW1 VIN VOUT A ON, B OFF PWM C, D SWITCHES D ON, C OFF PWM A, B SWITCHES FOUR SWITCH PWM 98% DMAX BOOST 3% DMIN BUCK DMIN BOOST DMAX BUCK BOOST REGION BUCK REGION BUCK/BOOST REGION 3780 F02 Figure 1. Simplified Diagram of the Output Switches Figure 2. Operating Mode vs Duty Cycle |
Similar Part No. - LTC3780IG |
|
Similar Description - LTC3780IG |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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
