 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3402 Datasheet(PDF) 11 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3402 Datasheet(HTML) 11 Page - Linear Technology |
|
|
11 / 36 page  LTC1871 11 1871fe APPLICATIONS INFORMATION Programming the Operating Frequency The choice of operating frequency and inductor value is a tradeoff between efficiency and component size. Low frequency operation improves efficiency by reducing MOSFET and diode switching losses. However, lower frequency operation requires more inductance for a given amount of load current. The LTC1871 uses a constant frequency architecture that can be programmed over a 50kHz to 1000kHz range with a single external resistor from the FREQ pin to ground, as shown in Figure 1. The nominal voltage on the FREQ pin is 0.6V, and the current that flows into the FREQ pin is used to charge and discharge an internal oscillator capacitor. A graph for selecting the value of RT for a given operating frequency is shown in Figure 6. INTVCC Regulator Bypassing and Operation An internal, P-channel low dropout voltage regulator pro- duces the 5.2V supply which powers the gate driver and logic circuitry within the LTC1871, as shown in Figure 7. The INTVCC regulator can supply up to 50mA and must be bypassed to ground immediately adjacent to the IC pins with a minimum of 4.7μF tantalum or ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the MOSFET gate driver. For input voltages that don’t exceed 7V (the absolute maximum rating for this pin), the internal low dropout regulator in the LTC1871 is redundant and the INTVCC pin can be shorted directly to the VIN pin. With the INTVCC pin shorted to VIN, however, the divider that programs the regulated INTVCC voltage will draw 10μA of current from the input supply, even in shutdown mode. For applications that require the lowest shutdown mode input supply cur- rent, do not connect the INTVCC pin to VIN. Regardless of whether the INTVCC pin is shorted to VIN or not, it is always necessary to have the driver circuitry bypassed with a 4.7μF tantalum or low ESR ceramic capacitor to ground immediately adjacent to the INTVCC and GND pins. In an actual application, most of the IC supply current is used to drive the gate capacitance of the power MOSFET. As a result, high input voltage applications in which a large power MOSFET is being driven at high frequencies can cause the LTC1871 to exceed its maximum junction Figure 6. Timing Resistor (RT) Value FREQUENCY (kHz) 100 300 1000 1871 F06 10 100 200 1000 900 800 700 600 500 400 0 Figure 7. Bypassing the LDO Regulator and Gate Driver Supply + 1.230V R2 R1 P-CH 5.2V DRIVER GATE CVCC 4.7μF CIN INPUT SUPPLY 2.5V TO 30V GND PLACE AS CLOSE AS POSSIBLE TO DEVICE PINS M1 1871 F07 INTVCC VIN GND LOGIC |
Similar Part No. - LTC3402 |
|
Similar Description - LTC3402 |
|
|
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
