 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3806 Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3806 Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 20 page  11 LTC3806 3806f The rising threshold voltage on the RUN pin is equal to the internal reference voltage of 1.230V. The comparator has 91mV of hysteresis to increase noise immunity. The turn-on and turn-off input voltage thresholds are programmed using a resistor divider according to the following formulas: VV R R VV R R IN OFF IN ON () () .• .• =+ =+ 1 139 1 2 1 1 230 1 2 1 The resistor R1 is typically chosen to be less than 1M. For applications where the RUN pin is only to be used as a logic input, the user should be aware of the 7V Absolute Maximum Rating for this pin! The RUN pin can be connected to the input voltage through an external 1M resistor, as shown in Figure 3c, for “always on” operation. Application Circuits A basic LTC3806 application circuit is shown in Figure 1. External component selection is driven by the character- istics of the load and the input supply. Duty Cycle Considerations Current and voltage stress on the power switch and synchronous rectifiers, input and output capacitor RMS currents and transformer utilization (size vs power) are impacted by duty factor. Unfortunately duty factor cannot be adjusted to simultaneously optimize all of these re- quirements. In general, avoid extreme duty factors since this severely impacts the current stress on most of the components. A reasonable target for duty factor is 50% at nominal input voltage. Using this rule of thumb, calculate the ideal transformer turns ratio: N V V D D IDEAL OUT IN = 1 1 • – APPLICATIO S I FOR ATIO For a 50% duty factor, this reduces to: N V V IDEAL OUT IN = 1 If NIDEAL is integer, use this for your turns ratio. If not, find a ratio of small integers that comes close to NIDEAL. If these conditions are met, bifilar winding techniques can be used that will improve coupling coefficient. Cross regulation will be better and primary-side snubbing may be reduced or eliminated. The selected turns ratio doesn’t have to be perfectly equal to NIDEAL because a flyback converter’s output voltage is not set through transformer action. Instead, the trans- former stores energy when the primary-side switch turns on and transfers this energy to the output(s) by flyback action when the primary-side switch turns off. Cross regulation may be improved by using a target duty factor which is less than 50%. This improves cross regulation because the secondary-side MOSFETs (syn- chronous rectifiers) will be on a larger percentage of the time (thereby increasing the average coupling between the outputs). Duty factor is reduced by proportionately in- creasing all turns ratios. Reduced duty factor has the following effect on MOSFET stresses: MOSFET MOSFET LOCATION CURRENT STRESS VOLTAGE STRESS Primary Increased Reduced Secondary Reduced Increased The duty factor with the selected turns ratio will equal: D V VN V OUT OUT IN = + () 1 1 • While the output(s)/input turns ratio are not critical, the turns ratio between outputs are critical and affect the accuracy of the slave output voltages. |
Similar Part No. - LTC3806 |
|
Similar Description - LTC3806 |
|
|
|
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
