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UC2855BN Fiches technique(PDF) 4 Page - Texas Instruments |
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UC2855BN Fiches technique(HTML) 4 Page - Texas Instruments |
4 / 12 page 4 UC2855A/B UC3855A/B ELECTRICAL CHARACTERISTICS:Unless otherwise specified: VCC = 18V, RT = 15k, RVS = 23k, CT = 470pF, CI = 150pF, VRMS = 1.5V, IAC = 100 µA, ISENSE = 0V, CAOUT = 4V, VAOUT= 3.5V, VSENSE = 3V. –40°C to 85°C (UC2855A/B), 0°C to 70 °C (UC3855A/B). PARAMETER TEST CONDITIONS MIN TYP MAX UNITS ZVT Reset Threshold 2.3 2.6 2.9 V Input Bias Current V = 2.5V, VCT =0 6 20 µA Propagation Delay Measured at ZVTOUT 100 ns Maximum Pulse Width 400 ns Output High Voltage lOUT = −100mA, VCC = 15V 12 12.8 V Output Low Voltage lOUT = 100mA 1 2.2 V lOUT = 10mA 300 900 mV Output Low (UVLO) lOUT = 50mA, VCC = 0V 0.9 1.5 V Output RISE/FALL Time CLOAD = 1nF 35 ns Output Peak Current CLOAD = 10nF 0.75 A Current Synthesizer ION to CS Offset VION = 0V 30 50 mV Cl Discharge Current IAC = 50 µA 105 118 140 µA IAC = 500 µA5 µA IAC Offset Voltage 0.3 0.65 1.1 V ION Buffer Slew Rate 10 V/ µs ION Input Bias Current VION =2V 2 15 µA RVS Output Voltage 23k from RVS to GND 2.87 3 3.13 V Note 1: Gain constant (K) = IAC VA V VIMO OUT RMS • • (– . ) () 15 2 at VRMS = 1.5V, VAOUT = 5.5V. PIN DESCRIPTIONS CA This is the inverting input to the current amplifier. Connect the required compensation components be- tween this pin and CAOUT. The common mode operating range for this input is between −0.3V and 5V. CAO: This is the output of the wide bandwidth current amplifier and one of the inputs to the PWM duty cycle comparator. The output signal generated by this amplifier commands the PWM to force the correct input current. The output can swing from 0.1V to 7.5V. CI: The level shifted current sense signal is impressed upon a capacitor connected between this pin and GND. The buffered current sense transformer signal charges the capacitor when the boost switch is on. When the switch is off, the current synthesizer discharges the ca- pacitor at a rate proportional to the dI/dt of the boost in- ductor current. In this way, the discharge current is approximately equal to 3 4 V RRVS IAC – . Discharging the CI capacitor in this fashion, a “recon- structed” version of the inductor current is generated us- ing only one current sense transformer. CS: The reconstructed inductor current waveform gener- ated on the CI pin is level shifted down a diode drop to this pin. Connect the current amplifier input resistor be- tween CS and the inverting input of the current amplifier. The waveform on this pin is compared to the multiplier output waveform through the average current sensing current amplifier. The input to the peak current limiting comparator is also connected to this pin. A voltage level greater than 1.5 volts on this pin will trip the comparator and disable the gate driver output. CT: A capacitor from CT to GND sets the PWM oscillator frequency according to the following equation: f CT ≈ • 1 11200 . Use a high quality ceramic capacitor with low ESL and ESR for best results. A minimum CT value of 200pF in- sures good accuracy and less susceptibility to circuit lay- out parasitics. The oscillator and PWM are designed to provide practical operation to 500kHz. GND: All voltages are measured with respect to this pin. All bypass and timing capacitors connected to GND should have leads as short and direct as possible. |
Numéro de pièce similaire - UC2855BN |
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Description similaire - UC2855BN |
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