 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC1624IS Datasheet(PDF) 9 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC1624IS Datasheet(HTML) 9 Page - Linear Technology |
|
|
9 / 28 page  9 LTC1624 APPLICATIONS INFORMATION ratings that are ideal for input capacitor applications. Consult the manufacturer for other specific recommend- ations. INTVCC Regulator An internal regulator produces the 5V supply that powers the drivers and internal circuitry within the LTC1624. Good VIN bypassing is necessary to supply the high transient currents required by the MOSFET gate drivers. High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maxi- mum junction temperature rating for the LTC1624 to be exceeded. The supply current is dominated by the gate charge supply current as discussed in the Efficiency Considerations section. The junction temperature can be estimated by using the equations given in Note 1 of the Electrical Characteristics table. For example, the LTC1624 is limited to less than 17mA from a 30V supply: TJ = 70°C + (17mA)(30V)(110°C/W) = 126°C To prevent maximum junction temperature from being exceeded, the input supply current must be checked operating in continuous mode at maximum VIN. Step-Down Converter: Topside MOSFET Driver Supply (CB, DB) An external bootstrap capacitor CB connectedtotheBOOST pin supplies the gate drive voltage for the topside MOSFET. Capacitor CB in the functional diagram is charged through internal diode DB from INTVCC when the SW pin is low. When the topside MOSFET is to be turned on, the driver places the CB voltage across the gate to source of the MOSFET. This enhances the MOSFET and turns on the topside switch. The switch node voltage SW rises to VIN and the BOOST pin rises to VIN + INTVCC. The value of the boost capacitor CB needs to be 50 times greater than the total input capacitance of the topside MOSFET. In most applications 0.1 µF is adequate. Significant efficiency gains can be realized by supplying topside driver operating voltage from the output, since the VIN current resulting from the driver and control currents will be scaled by a factor of (Duty Cycle)/(Efficiency). For 5V regulators this simply means connecting the BOOST monly used for design because even significant deviations do not offer much relief. Note that capacitor manufacturer’s ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor, or to choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. Always consult the manufacturer if there is any question. The selection of COUT is driven by the required effective series resistance (ESR). Typically, once the ESR require- ment is satisfied the capacitance is adequate for filtering. The output ripple ( ∆VOUT) is determined by: ∆∆ V I ESR fC OUT L OUT ≈+ 1 4 where f = operating frequency, COUT = output capacitance and ∆IL = ripple current in the inductor. The output ripple is highest at maximum input voltage since ∆IL increases with input voltage. With ∆IL = 0.4IOUT(MAX) the output ripple will be less than 100mV at maximum VIN, assuming: COUT Required ESR < 2RSENSE Manufacturers such as Nichicon, United Chemicon and SANYO should be considered for high performance through-hole capacitors. The OS-CON semiconductor dielectric capacitor available from SANYO has the lowest ESR(size) product of any aluminum electrolytic at a some- what higher price. Once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. In surface mount applications multiple capacitors may have to be paralleled to meet the ESR or RMS current handling requirements of the application. Aluminum elec- trolytic and dry tantalum capacitors are both available in surface mount configurations. In the case of tantalum it is critical that the capacitors are surge tested for use in switching power supplies. An excellent choice is the AVX TPS series of surface mount tantalums, available in case heights ranging from 2mm to 4mm. Other capacitor types include SANYO OS-CON, Nichicon WF series and Sprague 595D series and the new ceramics. Ceramic capacitors are now available in extremely low ESR and high ripple current |
Similar Part No. - LTC1624IS |
|
Similar Description - LTC1624IS |
|
|
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
