 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
750312557 Datasheet(PDF) 8 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
750312557 Datasheet(HTML) 8 Page - Linear Technology |
|
|
8 / 24 page  LT8300 8 8300f operaTion The LT8300 is a current mode switching regulator IC de- signed specially for the isolated flyback topology. The key problem in isolated topologies is how to communicate the output voltage information from the isolated secondary side of the transformer to the primary side for regulation. Historically, opto-isolators or extra transformer windings communicatethisinformationacrosstheisolationbound- ary. Opto-isolator circuits waste output power, and the extra components increase the cost and physical size of the power supply. Opto-isolators can also cause system issuesduetolimiteddynamicresponse,nonlinearity,unit- to-unitvariationandagingoverlifetime.Circuitsemploying extra transformer windings also exhibit deficiencies, as using an extra winding adds to the transformer’s physical size and cost, and dynamic response is often mediocre. The LT8300 samples the isolated output voltage through the primary-side flyback pulse waveform. In this manner, neither opto-isolator nor extra transformer winding is re- quired for regulation. Since the LT8300 operates in either boundary conduction mode or discontinuous conduction mode, the output voltage is always sampled on the SW pin when the secondary current is zero. This method im- proves load regulation without the need of external load compensation components. The LT8300 is a simple to use micropower isolated flyback converterhousedina5-leadTSOT-23package.Theoutput voltage is programmed with a single external resistor. By integratingtheloopcompensationandsoft-startinside,the part further reduces the number of external components. As shown in the Block Diagram, many of the blocks are similar to those found in traditional switching regulators including reference, regulators, oscillator, logic, current amplifier, current comparator, driver, and power switch. The novel sections include a flyback pulse sense circuit, a sample-and-hold error amplifier, and a boundary mode detector, as well as the additional logic for boundary conduction mode, discontinuous conduction mode, and low ripple Burst Mode operation. Boundary Conduction Mode Operation TheLT8300featuresboundaryconductionmodeoperation at heavy load, where the chip turns on the primary power switch when the secondary current is zero. Boundary conduction mode is a variable frequency, variable peak- current switching scheme. The power switch turns on and the transformer primary current increases until an internally controlled peak current limit. After the power switch turns off, the voltage on the SW pin rises to the output voltage multiplied by the primary-to-secondary transformer turns ratio plus the input voltage. When the secondary current through the output diode falls to zero, the SW pin voltage collapses and rings around VIN. A boundary mode detector senses this event and turns the power switch back on. Boundaryconductionmodereturnsthesecondarycurrent to zero every cycle, so parasitic resistive voltage drops do not cause load regulation errors. Boundary conduc- tion mode also allows the use of smaller transformers compared to continuous conduction mode and does not exhibit sub-harmonic oscillation. Discontinuous Conduction Mode Operation As the load gets lighter, boundary conduction mode in- creases the switching frequency and decreases the switch peakcurrentatthesameratio.Runningatahigherswitching frequency up to several MHz increases switching and gate charge losses. To avoid this scenario, the LT8300 has an additional internal oscillator, which clamps the maximum switching frequency to be less than 750kHz. Once the switching frequency hits the internal frequency clamp, the part starts to delay the switch turn-on and operates in discontinuous conduction mode. Low Ripple Burst Mode Operation Unlike traditional flyback converters, the LT8300 has to turn on and off at least for a minimum amount of time and with a minimum frequency to allow accurate sampling of the output voltage. The inherent minimum switch cur- rent limit and minimum switch-off time are necessary to guarantee the correct operation of specific applications. As the load gets very light, the LT8300 starts to fold back theswitchingfrequencywhilekeepingtheminimumswitch current limit. So the load current is able to decrease while still allowing minimum switch-off time for the sample- and-hold error amplifier. Meanwhile, the part switches betweensleepmodeandactivemode,therebyreducingthe |
Similar Part No. - 750312557 |
|
Similar Description - 750312557 |
|
|
|
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
