 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3736-2 Datasheet(PDF) 10 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3736-2 Datasheet(HTML) 10 Page - Linear Technology |
|
|
10 / 28 page  10 LTC3736-2 37362fa Main Control Loop The LTC3736-2 uses a constant frequency, current mode architecture with the two controllers operating 180 de- grees out of phase. During normal operation, the top external P-channel power MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the current comparator (ICMP) resets the latch. The peak inductor current at which ICMP resets the RS latch is determined by the voltage on the ITH pin, which is driven by the output of the error amplifier (EAMP). The VFB pin receives the output voltage feedback signal from an exter- nal resistor divider. This feedback signal is compared to the internal 0.6V reference voltage by the EAMP. When the load current increases, it causes a slight decrease in VFB relative to the 0.6V reference, which in turn causes the ITH voltage to increase until the average inductor current matches the new load current. While the top P-channel MOSFET is off, the bottom N-channel MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IRCMP, or the beginning of the next cycle. Shutdown, Soft-Start and Tracking Start-Up (RUN/SS and TRACK Pins) The LTC3736-2 is shut down by pulling the RUN/SS pin low. In shutdown, all controller functions are disabled and the chip draws only 9 µA.TheTGoutputsareheldhigh(off) and the BG outputs low (off) in shutdown. Releasing RUN/SS allows an internal 0.7 µA current source to charge up the RUN/SS pin. When the RUN/SS pin reaches 0.65V, the LTC3736-2’s two controllers are enabled. The start-up of VOUT1 is controlled by the LTC3736-2’s internal soft-start. During soft-start, the error amplifier EAMP compares the feedback signal VFB1 to the internal soft-start ramp (instead of the 0.6V reference), which rises linearly from 0V to 0.6V in about 1ms. This allows the output voltage to rise smoothly from 0V to its final value, while maintaining control of the inductor current. The 1ms soft-start time can be increased by connecting the optional external soft-start capacitor CSS between the RUN/SS and SGND pins. As the RUN/SS pin continues to OPERATIO rise linearly from approximately 0.65V to 1.3V (being charged by the internal 0.7 µA current source), the EAMP regulates the VFB1 proportionally linearly from 0V to 0.6V. The start-up of VOUT2 is controlled by the voltage on the TRACK pin. When the voltage on the TRACK pin is less than the 0.6V internal reference, the LTC3736-2 regulates the VFB2 voltage to the TRACK pin instead of the 0.6V reference. Typically, a resistor divider on VOUT1 is con- nected to the TRACK pin to allow the start-up of VOUT2 to “track” that of VOUT1. For one-to-one tracking during start- up, the resistor divider would have the same values as the divider on VOUT2 that is connected to VFB2. Light Load Operation (Pulse-Skipping or Continuous Conduction) (SYNC/FCB Pin) The LTC3736-2 can be enabled to enter high efficiency pulse-skipping operation or forced continuous conduc- tion mode at low load currents. To select pulse-skipping operation, tie the SYNC/FCB pin to a DC voltage above 0.6V (e.g., VIN). To select forced continuous operation, tie the SYNC/FCB to a DC voltage below 0.6V (e.g., SGND). This 0.6V threshold between pulse-skipping operation and forced continuous mode can be used in secondary wind- ing regulation as described in the Auxiliary Winding Con- trol Using SYNC/FCB Pin discussion in the Applications Information section. In forced continuous operation, the inductor current is allowed to reverse at light loads or under large transient conditions. The peak inductor current is determined by the voltage on the ITH pin. The P-channel MOSFET is turned on every cycle (constant frequency) regardless of the ITH pin voltage. In this mode, the efficiency at light loads is lower than in pulse-skipping operation. However, continuous mode has the advantages of lower output ripple and less interference with audio circuitry. When the SYNC/FCB pin is tied to a DC voltage above 0.6V or when it is clocked by an external clock source to use the phase-locked loop (see Frequency Selection and Phase- Locked Loop), the LTC3736-2 operates in PWM pulse- skipping mode at light loads. In this mode, the current comparator ICMP may remain tripped for several cycles and (Refer to Functional Diagram) |
Similar Part No. - LTC3736-2 |
|
Similar Description - LTC3736-2 |
|
|
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
