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FAN5234QSCX Datasheet(PDF) 5 Page - Fairchild Semiconductor |
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FAN5234QSCX Datasheet(HTML) 5 Page - Fairchild Semiconductor |
5 / 15 page FAN5234 PRODUCT SPECIFICATION REV. 1.0.10 5/3/04 5 Figure 2. IC Block Diagram REF2 PGOOD EN C BOOT Q1 Q2 5V VDD ADAPTIVE GATE CONTROL LOGIC CURRENT PROCESSING HDRV SW LDRV PGND BOOT VDD HYST ISNS VIN C OUT VOUT PWM/HYST PWM S/H ILIM R SENSE ILIM det. HYST SS SS DUTY CYCLE CLAMP Σ PWM SR Q RAMP MODE OSC I OU T RAMP CLK OVP POR/UVLO Reference and Soft Start FPWM L OU T VREF EA PWM/HYST VSEN FPWM VIN Circuit Description Overview The FAN5234 is a PWM controller intended for low voltage power applications in modern notebook, desktop, and sub-notebook PCs. The output voltage of the controller can be set in the range of 0.9V to 5.5V by an external resistor divider. The synchronous buck converter can operate from either an unregulated DC source (such as a notebook battery) with voltage ranging from 2V to 24V, or from a regulated system rail. In either mode of operation the IC is biased from a +5V source. The PWM modulator uses an average current mode control with input voltage feed-forward for simplified feed- back loop compensation and improved line regulation. The controller includes integrated feedback loop compensation that dramatically reduces the number of external compo- nents. Depending on the load level, the converter can operate either in fixed frequency PWM mode or in a hysteretic mode. Switch-over from PWM to hysteretic mode improves the converters' efficiency at light loads and prolongs battery run time. In hysteretic mode, a comparator is synchronized to the main clock that allows seamless transition between the oper- ational modes and reduced channel-to-channel interaction. The hysteretic mode of operation can be inhibited indepen- dently using the FPWM pin if variable frequency operation is not desired. Oscillator Table 1. Converter Operating modes When VIN is from the battery, the oscillator's ramp ampli- tude is proportional to VIN, providing voltage feed-forward control for improved loop response. When in either of the Fixed modes, oscillator's ramp amplitude is fixed. The oper- ating frequency is then determined according to the connec- tion on the VIN pin (Table 1). Initialization and Soft Start Assuming EN is high, FAN5234 is initialized when VCC exceeds the rising UVLO threshold. Should VCC drop below the UVLO threshold, an internal Power-On Reset function disables the chip. Mode FSW (Khz) Converter Power VIN Pin Battery 300 2 to 24V Battery (>5V) Fixed 300 300 < 5.5V Fixed 100K Ω to GND Fixed 600 600 < 5.5V Fixed GND |
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