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LM25088 Fiches technique(PDF) 8 Page - Texas Instruments |
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LM25088 Fiches technique(HTML) 8 Page - Texas Instruments |
8 / 33 page FB VIN VCC SW RT Regulator DRIVER BOOT LEVEL SHIFT THERMAL SHUTDOWN UVLO ERROR AMP DIS COMP TRACK SAMPLE and HOLD CLK GND CLK CSG CS CLK RAMP GENERATOR + SHUTDOWN PWM I- LIMIT OUT RAMP SS VIN STANDBY 5 uA 1.2 VIN EN Ir HG CLK S R Q Q CLK FREQUENCY DITHERING STANDBY SYNC DITHER LM5088 -1 ONLY OSCILLATOR HICCUP RESTART LOGIC Rs RFB1 DITHER RES RFB2 Q L D VOUT CBOOT UVLO MINIMUM OFF- TIME LOGIC 7.7V HICCUP RESTART LM5088 - 2 ONLY 5V A = -10 CRES/DITH CSYNC 1.2V RUV2 RUV1 CFT CIN CSS CHF RCOMP CCOMP RRT CRAMP COUT 0.9V 0.4V 5V 11 uA CVCC LM25088 VIN (4.5V-42V) 1.205V LM25088 SNVS609G – DECEMBER 2008 – REVISED MARCH 2011 www.ti.com Block Diagram Figure 15. Block Diagram DETAILED OPERATION The LM25088 Wide Input Range Buck Controller features all the functions necessary to implement an efficient high voltage step-down converter using a minimum number of external components. The control method is based on peak current mode control utilizing an emulated current ramp. Peak current mode control provides inherent line voltage feed-forward, cycle-by-cycle current limiting and ease of loop compensation. The use of an emulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable processing of very small duty cycles necessary in high input voltage applications. The operating frequency is user programmable from 50 kHz to 1 MHz. The LM25088-1 provides a ±5% frequency dithering function to reduce the conducted and radiated EMI, while the LM25088-2 provides a versatile restart timer for overload protection. Additional features include the low dropout bias regulator, tri-level enable input to control shutdown and standby modes, soft-start, and voltage tracking and oscillator synchronization capability. The device is available in a thermally enhanced HTSSOP-16 pin package. The functional block diagram and typical application schematic of the LM25088 are shown in Figure 15. The LM25088 is well suited for a wide range of applications where efficient step-down of high, unregulated input voltage is required. The LM25088’s typical applications include Telecom, Industrial and Automotive. High Voltage Low-Dropout Regulator The LM25088 contains a high voltage, low-dropout regulator that provides the VCC bias supply for the controller and the bootstrap MOSFET gate driver. The input pin (VIN) can be connected directly to an input voltage as high as 42V. The output of the VCC regulator (7.8V) is internally current limited to 25 mA. Upon power up, the regulator sources current into the capacitor connected to the VCC pin. When the voltage at the VCC pin exceeds the upper VCC UV threshold of 4.0V and the EN pin is greater than 1.2 Volts, the output (HG) is enabled and a soft-start sequence begins. The output is terminated if VCC falls below its lower UV threshold (3.8V) or the EN pin falls below 1.1V. When VIN is less than VCC regulation point of 7.8V, then the internal pass device acts as a switch. Thereby, VCC tracks VIN with a voltage drop determined by the RDS(ON) of the internal switch and operating current of the controller. The required VCC capacitor value is dependant on system startup characteristics with a minimum value no less than 0.1 µF. 8 Submit Documentation Feedback Copyright © 2008–2011, Texas Instruments Incorporated Product Folder Links: LM25088 |
Numéro de pièce similaire - LM25088_14 |
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Description similaire - LM25088_14 |
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