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UC3874Q-2 Datasheet(PDF) 4 Page - Texas Instruments |
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UC3874Q-2 Datasheet(HTML) 4 Page - Texas Instruments |
4 / 10 page 4 UC1874-1,-2 UC2874-1,-2 UC3874-1,-2 ELECTRICAL CHARACTERISTICS: Unless otherwise stated these specifications apply for TA = –55°C to +125°C for UC1874; TA = –25°C to +85°C for UC2874; 0°C to +70°C for UC3874; VCC = 12V, Ct = 680pF, CCAP = 1 F; CBOOT = 0.1 F; TA =TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Sleep/Soft start/Bootstrap Section (continued) Bootstrap Regulation Voltage UCX874-2, Low Driver ON 9.5 10.2 12.5 V UCX874-1, Low Driver ON 6 7.5 9 V Bootstrap Refresh Voltage UCX874-2, VCAOUT >VCTPEAK 789 V UCX874-1, VCAOUT >VCTPEAK 2.7 3.5 4 V High Side Driver Output Section Output High Voltage IOUT = –50mA, Boot = 23V 21 22.2 V Output Low Voltage IOUT = 50mA 1 2.2 V IOUT = 10mA 300 500 mV Output Low (UVLO) IOUT = 50mA, VCC = 0V 0.9 1.5 V Output Rise Time COUT = 1nF 40 160 ns Output Fall Time COUT = 1nF 30 100 ns Low Side Driver Output Section Output High Voltage IOUT = –50mA, VCAP = 11V 8.8 9.5 V Output Low Voltage IOUT = 50mA 1 2.2 V IOUT = 10mA 300 500 mV Output Low (UVLO) IOUT = 50mA, VCC = 0V 0.9 1.5 V Output Rise/Fall Time CLOAD = 1nF 40 160 ns Output Fall Time COUT = 1nF 30 100 ns X10 Amplifier Section Gain VISNS ± VISNS = 20mV to 80mV 9.2 9.8 10.4 V/V Slew Rate Rising TA = 25°C 1 1.4 V/ s Slew Rate Falling TA = 25°C 2 3.5 V/ s Input Resistance TA = 25°C 60 100 165 k PIN DESCRIPTIONS BOOT: This pin provides the high side rail for the HDRIVE output. An external capacitor (CBST)is connected between this pin and the drain of the external low side MOSFET. When the low side MOSFET is conducting Cbst is charged to 11V via an external diode tied to CAP. When the low side MOSFET turns off and the high side MOSFET turns on, the Cbst bootstraps itself up with the source of high side MOSFET, ultimately providing a 10V Vgs for the upper MOSFET. Since this 10V is referenced to the source of the high side N-channel MOSFET, the actual voltage on BOOT and HDRIVE is approximately 10V above VCC while the high side MOSFET is conducting. The voltage on BOOT is continuously monitored during low input voltage conditions when the duty cycle equals approximately 100% to insure that a sufficient gate drive level is being supplied by the UC3874. If the voltage on BOOT falls below 8V (UC3874-2) or 3.5V (UC3874-1), the IC forces the low side driver to cycle itself on for the few cycles required to replenish CBST. In this way, virtual 100% duty cycle operation is provided. CA-: This is the inverting input to the current amplifier. Connect a series resistor and capacitor between this pin and CAOUT to set the current loop compensation. An in- put resistor between this pin and ISOUT provides the in- ductor current sense signal to the amplifier and also sets the high frequency gain of the amplifier. The com- mon mode operating range for this input is between GND and 4V. The normal range during operation is between 2V and 3V. CAOUT: 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 duty cycle to maintain output voltage in regulation. The output can swing from 0.1V to 4V. |
Similar Part No. - UC3874Q-2 |
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Similar Description - UC3874Q-2 |
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