Moteur de recherche de fiches techniques de composants électroniques |
|
LM2727 Fiches technique(PDF) 10 Page - Texas Instruments |
|
LM2727 Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 32 page LM2727, LM2737 SNVS205D – AUGUST 2002 – REVISED MARCH 2013 www.ti.com APPLICATION INFORMATION THEORY OF OPERATION The LM2727 is a voltage-mode, high-speed synchronous buck regulator with a PWM control scheme. It is designed for use in set-top boxes, thin clients, DSL/Cable modems, and other applications that require high efficiency buck converters. It has power good (PWRGD), output shutdown (SD), over voltage protection (OVP) and under voltage protection (UVP). The over-voltage and under-voltage signals are OR gated to drive the Power Good signal and a shutdown latch, which turns off the high side gate and turns on the low side gate if pulled low. Current limit is achieved by sensing the voltage VDS across the low side FET. During current limit the high side gate is turned off and the low side gate turned on. The soft start capacitor is discharged by a 95µA source (reducing the maximum duty cycle) until the current is under control. The LM2737 does not latch off during UVP or OVP, and uses the HIGH and LOW comparators for the powergood function only. START UP When VCC exceeds 4.2V and the enable pin EN sees a logic high the soft start capacitor begins charging through an internal fixed 10µA source. During this time the output of the error amplifier is allowed to rise with the voltage of the soft start capacitor. This capacitor, Css, determines soft start time, and can be determined approximately by: (1) An application for a microprocessor might need a delay of 3ms, in which case CSS would be 12nF. For a different device, a 100ms delay might be more appropriate, in which case CSS would be 400nF. (390 10%) During soft start the PWRGD flag is forced low and is released when the voltage reaches a set value. At this point this chip enters normal operation mode, the Power Good flag is released, and the OVP and UVP functions begin to monitor Vo. NORMAL OPERATION While in normal operation mode, the LM2727/37 regulates the output voltage by controlling the duty cycle of the high side and low side FETs. The equation governing output voltage is: (2) The PWM frequency is adjustable between 50kHz and 2MHz and is set by an external resistor, RFADJ, between the FREQ pin and ground. The resistance needed for a desired frequency is approximately: (3) MOSFET GATE DRIVERS The LM2727/37 has two gate drivers designed for driving N-channel MOSFETs in a synchronous mode. Power for the drivers is supplied through the BOOTV pin. For the high side gate (HG) to fully turn on the top FET, the BOOTV voltage must be at least one VGS(th) greater than Vin. (BOOTV ≥ 2*Vin) This voltage can be supplied by a separate, higher voltage source, or supplied from a local charge pump structure. In a system such as a desktop computer, both 5V and 12V are usually available. Hence if Vin was 5V, the 12V supply could be used for BOOTV. 12V is more than 2*Vin, so the HG would operate correctly. For a BOOTV of 12V, the initial gate charging current is 2A, and the initial gate discharging current is typically 6A. 10 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated Product Folder Links: LM2727 LM2737 |
Numéro de pièce similaire - LM2727_15 |
|
Description similaire - LM2727_15 |
|
|
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 |