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UCC3857DWTR Datasheet(PDF) 4 Page - Texas Instruments |
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UCC3857DWTR Datasheet(HTML) 4 Page - Texas Instruments |
4 / 11 page 4 UCC1857 UCC2857 UCC3857 PIN DESCRIPTIONS AGND: Reference point of the internal reference and all thresholds, as well as the return for the remainder of the device except for the output drivers. CA–: Inverting input of the inner current loop error ampli- fier. CAO: Output of the inner current loop error amplifier. This output can swing between approximately 0.2V and 6V. It is one of the inputs to the PWM comparator. VAO: This is the output of the voltage loop error ampli- fier. It is internally clamped to approximately 5.6V by the UCC3857 and can swing as low as approximately 0.1V. Voltages below 0.5V on VAO will disable the MOSDRV output and force the IGDRV1 and IGDRV2 outputs to a zero overlap condition. CRMS: A capacitor is connected between CRMS and ground to average the AC line voltage over a half cycle. CRMS is internally connected to the RMS detection cir- cuitry. CT: A capacitor (low ESR, ESL) is tied between CT and ground to set the ramp generator switching frequency in conjunction with RT. The ramp generator frequency is ap- proximately given by: f RC SW TT ≈ 0.67 • . DELAY: A resistor to VREF and a capacitor to AGND are connected to DELAY to set the overlap delay time for the MOSDRV output stage. The overlap delay function can be disabled by removing the capacitor to AGND. IAC: A resistor is connected to the rectified AC input line voltage from IAC. This provides the internal multiplier and the RMS detector with instantaneous line voltage in- formation. IGDRV1: Driver output for one of the two external IGBT power switches. IGDRV2: Driver output for one of the two external IGBT power switches. MOSDRV: Driver output for the external power MOSFET switch. MOUT: Output of the analog multiply and divide circuit. The output current from MOUT is fed into a resistor to the return leg of the input bridge. The resultant waveform forms the sine reference for the current error amplifier. PKLMT: Inverting input of the peak current limit com- parator. The threshold for this comparator is nominally set to 0V. The peak limit comparator terminates the MOSDRV, IGDRV1 and IGDRV2 outputs when tripped. PGND: Return for all high level currents, internally tied to the output driver stages of the UCC3857. RT: A resistor, RT is tied between RT and ground to set the charging current for the internal ramp generator. The UCC3857 provides a temperature compensated 3.0V at RT. The oscillator charging current is therefore: 3.0V/RT. Current out of RT should be limited to 250 µA for best performance. VA–: This is the feedback input for the outer voltage con- trol loop. An external opto isolator circuit provides the ELECTRICAL CHARACTERISTICS: Unless otherwise stated, these specifications apply for TA = 0°C to 70°C for the UCC3857, –40°C to +85°C for the UCC2857, and –55°C to +125°C for the UCC1857, VVIN, VVD = 12V, RT = 19.2K, CT = 680pF. TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Soft Start Charge Current 10 µA Shutdown Comparator Threshold Measured on SS 0 0.4 V Multiplier Output Current, IAC Limited IAC = 100µA, VVAO = 5.5V, VCRMS = 0V –200 µA Output Current, Power Limited IAC = 100µA, VVAO = 5.5V, VCRMS = 1V –200 µA Output Current, Zero IAC = 0 –2 0 2 µA Gain Constant 2.5 1/V Zero Power, Peak Current Zero Power Comparator Threshold Measured on VAO 0.5 V Peak Current Limit Comparator Threshold Measured on PKLMT 0 V Note 1: Common mode voltages = 0V, VCAO = 3V |
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