 |
전자부품 데이터시트 검색엔진 |
|
|
전자부품 데이터시트 검색엔진 |
|
LM2653MTC-ADJ 데이터시트(PDF) 9 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM2653MTC-ADJ 데이터시트(HTML) 9 Page - National Semiconductor (TI) |
|
|
9 / 12 page  Design Procedure (Continued) R 1 and R2 (PROGRAMMING OUTPUT VOLTAGE) Use the following formula to select the appropriate resistor values: V OUT =VREF(1+R1/R2) where V REF = 1.238V Select resistors between 10k Ω and 100kΩ. (1% or higher accuracy metal film resistors for R 1 and R2.) COMPENSATION COMPONENTS In the control to output transfer function, the first pole F p1 can be estimated as 1/(2 πR OUTCOUT); The ESR zero Fz1 of the output capacitor is 1/(2 πESRC OUT); Also, there is a high frequency pole F p2 in the range of 45kHz to 150kHz: F p2 =Fs/( πn(1−D)) whereD=V OUT/VIN, n = 1+0.348L/(VIN−VOUT)(L isinµHs and V IN and VOUT in volts). The total loop gain G is approximately 500/I OUT where IOUT is in amperes. A Gm amplifier is used inside the LM2653. The output resis- tor R o of the Gm amplifier is about 80k Ω.C c1 and RC together with R o give a lag compensation to roll off the gain: F pc1 = 1/(2 πC c1(Ro+Rc)), Fzc1 = 1/2 πC c1Rc. In some applications, the ESR zero F z1 can not be cancelled by F p2. Then, Cc2 is needed to introduce Fpc2 to cancel the ESR zero, F p2 = 1/(2 πC c2Ro\Rc). The rule of thumb is to have more than 45˚ phase margin at the crossover frequency (G=1). If C OUT is higher than 68µF, Cc1 = 2.2nF, and Rc = 15K Ω are good choices for most applications. If the ESR zero is too low to be cancelled by F p2, add Cc2. If the transient response to a step load is important, choose R C to be higher than 10k Ω. EXTERNAL SCHOTTKY DIODE A Schottky diode D 1 is recommended to prevent the intrinsic body diode of the low-side MOSFET from conducting during the deadtime in PWM operation and hysteretic mode when both MOSFETs are off. If the body diode turns on, there is extra power dissipation in the body diode because of the reverse-recovery current and higher forward voltage; the high-side MOSFET also has more switching loss since the negative diode reverse-recovery current appears as the high-side MOSFET turn-on current in addition to the load current. These losses degrade the efficiency by 1-2%. The improved efficiency and noise immunity with the Schottky diode become more obvious with increasing input voltage and load current. The breakdown voltage rating of D 1 is preferred to be 25% higher than the maximum input voltage. Since D 1 is only on for a short period of time, the average current rating for D 1 only requires being higher than 30% of the maximum output current. It is important to place D 1 very close to the drain and source of the low-side MOSFET, extra parasitic inductance in the parallel loop will slow the turn-on of D 1 and direct the current through the body diode of the low-side MOSFET. PCB Layout Considerations Layout is critical to reduce noises and ensure specified performance. The important guidelines are listed as follows: 1. Minimize the parasitic inductance in the loop of input capacitors and the internal MOSFETs by connecting the input capacitors to V IN and PGND pins with short and wide traces. This is important because the rapidly switching current, together with wiring inductance can generate large voltage spikes that may result in noise problems. 2. Minimize the trace from the center of the output resistor divider to the FB pin and keep it away from noise sources to avoid noise pick up. For applications require tight regulation at the output, a dedicated sense trace (separated from the power trace) is recommended to connect the top of the resistor divider to the output. 3. If the Schottky diode D 1 is used, minimize the traces connecting D 1 to SW and PGND pins. 10104901 Schematic for the Typical Board Layout www.national.com 9 |
유사한 부품 번호 - LM2653MTC-ADJ |
|
유사한 설명 - LM2653MTC-ADJ |
|
|
|
링크 URL |
| 개인정보취급방침 |
| ALLDATASHEET.CO.KR |
| ALLDATASHEET 가 귀하에 도움이 되셨나요? [ DONATE ] |
Alldatasheet는? | 광고문의 | 운영자에게 연락하기 | 개인정보취급방침 | 링크교환 | 제조사별 검색 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 |
Korean ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
