công cụ tìm kiếm bảng dữ liệu linh kiện điện tử |
|
LM20242 bảng dữ liệu(PDF) 10 Page - Texas Instruments |
|
|
LM20242 bảng dữ liệu(HTML) 10 Page - Texas Instruments |
10 / 28 page LM20242 SNVS534D – OCTOBER 2007 – REVISED MAY 2008 www.ti.com OPERATION DESCRIPTION GENERAL The LM20242 switching regulator features all of the functions necessary to implement an efficient low voltage buck regulator using a minimum number of external components. This easy to use regulator features two integrated switches and is capable of supplying up to 2A of continuous output current. The regulator utilizes peak current mode control with nonlinear slope compensation to optimize stability and transient response over the entire output voltage range. Peak current mode control also provides inherent line feed-forward, cycle-by-cycle current limiting and easy loop compensation. The switching frequency can be varied from 100 kHz to 1 MHz with an external resistor to ground. The device can operate at high switching frequency allowing use of a small inductor while still achieving efficiencies as high as 93%. The precision internal voltage reference allows the output to be set as low as 0.8V. Fault protection features include: current limiting, thermal shutdown, over voltage protection, and shutdown capability. The device is available in the HTSSOP package featuring an exposed pad to aid thermal dissipation. The typical application circuit for the LM20242 is shown in Figure 9 in the design guide. PRECISION ENABLE The enable (EN) pin allows the output of the device to be enabled or disabled with an external control signal. This pin is a precision analog input that enables the device when the voltage exceeds 1.25V (typical). The EN pin has 50 mV of hysteresis and will disable the output when the enable voltage falls below 1.2V (typical). If the EN pin is not used, it should be disconnected so the internal 2 µA pull-up will default this function to the enabled condition. Since the enable pin has a precise turn-on threshold it can be used along with an external resistor divider network from VIN to configure the device to turn-on at a precise input voltage. The precision enable circuitry will remain active even when the device is disabled. PEAK CURRENT MODE CONTROL In most cases, the peak current mode control architecture used in the LM20242 only requires two external components to achieve a stable design. The compensation can be selected to accommodate any capacitor type or value. The external compensation also allows the user to set the crossover frequency and optimize the transient performance of the device. For duty cycles above 50% all current mode control buck converters require the addition of an artificial ramp to avoid sub-harmonic oscillation. This artificial linear ramp is commonly referred to as slope compensation. What makes the LM20242 unique is the amount of slope compensation will change depending on the output voltage. When operating at high output voltages the device will have more slope compensation than when operating at lower output voltages. This is accomplished in the LM20242 by using a non-linear parabolic ramp for the slope compensation. The parabolic slope compensation of the LM20242 is much better than the traditional linear slope compensation because it optimizes the stability of the device over the entire output voltage range. CURRENT LIMIT The precise current limit enables the device to operate with smaller inductors that have lower saturation currents. When the peak inductor current reaches the current limit threshold, an over current event is triggered and the internal high-side FET turns off and the low-side FET turns on, allowing the inductor current to ramp down until the next switching cycle. For each sequential over-current event, the reference voltage is decremented and PWM pulses are skipped resulting in a current limit that does not aggressively fold back for brief over-current events, while at the same time providing frequency and voltage foldback protection during hard short circuit conditions. SOFT-START AND VOLTAGE TRACKING The SS/TRK pin is a dual function pin that can be used to set the startup time or track an external voltage source. The startup or soft-start time can be adjusted by connecting a capacitor from the SS/TRK pin to ground. The soft-start feature allows the regulator output to gradually reach the steady state operating point, thus reducing stresses on the input supply and controlling startup current. If no soft-start capacitor is used the device defaults to the internal soft-start circuitry resulting in a startup time of approximately 1 ms. For applications that require a monotonic startup or utilize the PGOOD pin, an external soft-start capacitor is recommended. The SS/TRK pin can also be set to track an external voltage source. The tracking behavior can be adjusted by two external resistors connected to the SS/TRK pin as shown in Figure 14 in the design guide. 10 Submit Documentation Feedback Copyright © 2007–2008, Texas Instruments Incorporated Product Folder Links: LM20242 |
Số phần tương tự - LM20242 |
|
Mô tả tương tự - LM20242 |
|
|
Link URL |
Chính sách bảo mật |
ALLDATASHEET.VN |
Cho đến nay ALLDATASHEET có giúp ích cho doanh nghiệp của bạn hay không? [ DONATE ] |
Alldatasheet là | Quảng cáo | Liên lạc với chúng tôi | Chính sách bảo mật | Trao đổi link | Tìm kiếm theo nhà sản xuất 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 |