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UC3750G-XX-AF5-R датащи(PDF) 5 Page - Unisonic Technologies |
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UC3750G-XX-AF5-R датащи(HTML) 5 Page - Unisonic Technologies |
5 / 8 page UC3750 Preliminary CMOS IC UNISONICTECHNOLOGIESCO.,LTD 5 of 8 www.unisonic.com.tw QW-R502-360.b DESCRIPTION INFORMATION 1. Detailed Operating Description The UTC UC3750 is a step-down DC−DC controllers designed specially in portable applications powered by battery cells. The UTC UC3750 combines the advantages of Pulse frequency modulation (PFM) and Constant-frequency pulse width modulation (PWM) which can provide excellent efficiency with light loads and high efficiency and low output voltage ripple at heavy loads respectively. This device can provide up to 2.0 A loading current with appropriate external P-type MOSFET connected. Because of working at high switching frequency, it’ s possible to use small size surface mount inductor and capacitors to reduce PCB area and provide better interference handling for noise sensitive applications. 2. The Internal Oscillator The UTC UC3750 needs an oscillator to govern the switching of a PWM control cycles. The UTC UC3750 has an internal Fixed− frequency oscillator. The oscillator signal generates all the using timing signals. And the oscillator frequency is set to 600 kHz ±15%. 3. Voltage Reference and Soft-Start The UTC UC3750 has a built-in soft-start (SS) circuit that controls the ramping up of the internal reference voltage during the power-up of the converter. This function effectively enables the output voltage rise gradually over the specified soft-start time (8 ms typ.), which prevents the output voltage from overshooting during startup of the converter. The UTC UC3750 includes an internal high accuracy voltage reference. This reference voltage is connected to the inverting input terminal of the error amplifier (EA), A1, which compared with portion of the output voltage that is derived from an integrated voltage divider with precise trimming to give the required output voltage with ±2% accuracy. 4. Voltage Mode Pulse width modulation (PWM) Control Scheme The UTC UC3750 is working in constant-frequency pulse width modulation (PWM) voltage mode control. The controller operates with the internal oscillator which generates the required ramp function to compare with the output of the error amplifier (EA), A1. The error amplifier (EA) compares the internally divided-down output voltage with the voltage reference to produce an error voltage at its output. This error voltage is compared with the ramp function to generate the control pulse to drive the external power switch. On a cycle-by-cycle basis, the greater the error voltage is greater; the switch is held on longer. Hence, corresponding corrective action will be made to keep the output voltage within regulation. Constant-frequency PWM reduces output voltage ripple and noise, which is one of the important characteristics for noise sensitive communication applications. The high switching frequency allows small size surface mount components to improve layout compactness, reducing PC board area, eliminating audio and emission interference. 5. Power-Saving Pulse-Frequency-Modulation (PFM) Control Scheme The converter enters the discontinuous conduction mode (DCM) operation when the load is decreasing, which means the inductor current will decrease to 0 before the next switching cycle starts. In DCM operation, the ON time for each switching cycle will decrease significantly when the output current decreases. In order to maintain high conversion efficiency even at light load conditions, the ON time for each switching cycle is closely monitored and for any ON time is smaller than the preset value (320 ns), the switching pulse will be skipped. As a result, when the loading current is small, the converter will be operating in a “Constant ON time (320 ns nominal), variable OFF time” Pulse frequency modulation (PFM) mode. This innovative control scheme improves the conversion efficiency for the system at light load and standby operating conditions hence extend the operating life of the battery. 6. Low Power Shutdown Mode Once the CE pin is tied to GND the UTC UC3750 can’t work. In shutdown mode, the internal reference, oscillator, control circuitry, driver and internal feedback voltage divider are turned off and the output voltage falls to 0 V. Because most of the internal circuits can’t work and the current paths are cut-off, the device consume rather small in this condition. 7. Under-Voltage Lockout (UVLO) The UTC UC3750 incorporated the UVLO to prevent operation of the P-channel MOSFET below rated input voltage levels. The comparator will turn-off the control circuitry and shut the converter down, once the input supply voltage drops below about 2.2 V. |
Аналогичный номер детали - UC3750G-XX-AF5-R |
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Аналогичное описание - UC3750G-XX-AF5-R |
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