 |
Moteur de recherche de fiches techniques de composants électroniques |
|
|
Moteur de recherche de fiches techniques de composants électroniques |
|
LMQ61460 Fiches technique(PDF) 33 Page - Texas Instruments |
|
|
||||||||||||||||||||||||||||||
LMQ61460 Fiches technique(HTML) 33 Page - Texas Instruments |
|
|
33 / 55 page  been generated assuming typical derating for 16 V, X7R capacitors. If lower voltage, non-automotive grade, or lower temperature rated capacitors are used, more capacitors than listed will likely be needed. 8.2.2.5 Input Capacitor Selection The ceramic input capacitors provide a low impedance source to the converter in addition to supplying the ripple current and isolating switching noise from other circuits. A minimum of 10 μF of ceramic capacitance is required on the input of the device. This must be rated for at least the maximum input voltage that the application requires; preferably twice the maximum input voltage. This capacitance can be increased to help reduce input voltage ripple and maintain the input voltage during load transients. In addition, a small case size 100-nF ceramic capacitor must be used at each input/ground pin pair, VIN1/PGND1 and VIN2/PGND2, immediately adjacent to the converter. This provides a high-frequency bypass for the control circuits internal to the device. These capacitors also suppress SW node ringing, which reduces the maximum voltage present on the SW node and EMI. The two 100 nF must also be rated at 50 V with an X7R or better dielectric. The VQFN-HR (RJR) package provides two input voltage pins and two power ground pins on opposite sides of the package. This allows the input capacitors to be split, and placed optimally with respect to the internal power MOSFETs, thus improving the effectiveness of the input bypassing. In this example, two 4.7-μF and two 100-nF ceramic capacitors are used, one at each VIN/PGND location. A single 10-μF can also be used on one side of the package. Many times, it is desirable and necessary to use an electrolytic capacitor on the input in parallel with the ceramics. This is especially true if long leads or traces are used to connect the input supply to the converter. The moderate ESR of this capacitor can help damp any ringing on the input supply caused by the long power leads. The use of this additional capacitor also helps with momentary voltage dips caused by input supplies with unusually high impedance. Most of the input switching current passes through the ceramic input capacitors. The approximate worst case RMS value of this current can be calculated from Equation 12 and must be checked against the manufacturers' maximum ratings. I RMS § I OUT 2 (12) 8.2.2.6 BOOT Capacitor The device requires a bootstrap capacitor connected between the CBOOT pin and the SW pin. This capacitor stores energy that is used to supply the gate drivers for the high-side power MOSFET. A high-quality (X7R) ceramic capacitor of 100 nF and at least 10 V is required. 8.2.2.7 BOOT Resistor A BOOT resistor can be connected between the CBOOT and RBOOT pins. Unless EMI for the application being designed is critical, these two pins can be shorted. A 100 Ω resistor between these pins eliminates overshoot. Even with 0 Ω, overshoot and ringing are minimal, less than 2 V if input capacitors are placed correctly. A boot resistor of 100 Ω, which corresponds to approximately 2.7 ns SW node rise time and decreases efficiency by approximately 0.5% at 2 MHz. To maximize efficiency, 0 Ω is chosen for this example. Under most circumstances, selecting an RBOOT resistor value above 100 Ω is undesirable since the resulting small improvement in EMI is not enough to justify further decreased efficiency. 8.2.2.8 VCC The VCC pin is the output of the internal LDO used to supply the control circuits of the converter. This output requires a 1-μF, 16-V ceramic capacitor connected from VCC to AGND for proper operation. In general, avoid loading this output with any external circuitry. However, this output can be used to supply the pullup for the power-good function (see Section 7.3.5). A pullup resistor with a value of 100 kΩ is a good choice in this case. Note, VCC will remain high when VEN_WAKE< EN < VEN. The nominal output voltage on VCC is 3.3 V. Do not short this output to ground or any other external voltage. www.ti.com LMQ61460 SNVSBR8A – JULY 2020 – REVISED AUGUST 2020 Copyright © 2020 Texas Instruments Incorporated Submit Document Feedback 33 Product Folder Links: LMQ61460 |
Numéro de pièce similaire - LMQ61460 |
|
Description similaire - LMQ61460 |
|
|
Lien URL |
| Politique de confidentialité |
| ALLDATASHEET.FR |
| ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants 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 |
French ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
