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UC2874N-1 Fiches technique(PDF) 6 Page - Texas Instruments |
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UC2874N-1 Fiches technique(HTML) 6 Page - Texas Instruments |
6 / 12 page 6 UC1874-1,-2 UC2874-1,-2 UC3874-1,-2 VREF: VREF is the output of the precision reference. The output is capable of supplying 20mA to peripheral circuitry and is internally short circuit current limited. VREF is disabled and low whenever VCC is below the UVLO threshold, and when SS is pulled below 0.5V. A VREF “good” comparator senses VREF and disables the PWM stage until VREF has attained approximately 90% of its nominal value. Bypass VREF to GND with a 0.1mF ceramic capacitor for best performance. VSNS: This pin is the inverting input of the voltage ampli- fier and serves as the output voltage feedback point for the synchronous regulator. It senses the output voltage through a voltage divider which produces a nominal 2.0V. OPERATION: Refer to 5V, 25W Application Schematic The UC3874 employs a fixed frequency average current mode control buck topology to convert a higher battery voltage down to a tightly regulated output voltage. Spe- cial design techniques allow this bipolar IC to deliver ex- ceptional performance while consuming approximately 6mA of supply current over an input voltage range of 4.5 to 35 volts. Fixed frequency operation allows synchroni- zation to an existing system clock, and easier filtering. Average current mode control provides inherent slope compensation and accurate short circuit current limiting. An additional benefit is its ability to maintain a constant regulator gain regardless of whether the inductor current is continuous or discontinuous. The output inductor current is sensed by an external low value shunt resistor (Rsense). This signal at full load current should be no larger than 100mV in order to mini- mize sensing losses. The differential voltage across Rsense is amplified by the internal X10 instrumentation amplifier. The common mode input range for this ampli- fier extends from GND to VCC in order to maintain accu- rate current sensing under normal conditions as well as abnormal conditions such as output short circuit and low drop out (LDO) modes. The output of the X10 instrumen- tation amplifier is applied to the inverting input of the cur- rent amplifier through an external resistor. The converter’s output voltage feedback is applied to the APPLICATION DIAGRAM UDG-95006-1 |
Numéro de pièce similaire - UC2874N-1 |
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Description similaire - UC2874N-1 |
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