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UC1914 датащи(PDF) 4 Page - Texas Instruments |
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UC1914 датащи(HTML) 4 Page - Texas Instruments |
4 / 14 page 4 UC1914 UC2914 UC3914 PIN DESCRIPTIONS CT: A capacitor is connected to this pin in order to set the maximum fault time. The minimum fault time must be more than the time to charge external load capacitance. The fault time is defined as: T CT I FAULT CH = • 2 where ICH = 100µA+IPL, where IPL is the current into the power limit pin. Once the fault time is reached the output will shutdown for a time given by: T CT I SD DIS = • 2 where IDIS is nominally 3µA. FAULT: Open collector output which pulls low upon any of the following conditions: Timer fault, Shutdown, UVLO. This pin MUST be pulled up to VCC or another supply through a suitable impedance. GND: Ground reference for the IC. IMAX: This pin programs the maximum allowable sourcing current. Since REF is a –2V reference (with re- spect to VCC), a voltage divider can be derived from VCC to REF in order to generate the program level for the IMAX pin. The current level at which the output ap- pears as a current source is equal to the voltage on the IMAX pin, with respect to VCC, divided by the current sense resistor. If desired, a controlled current startup can be programmed with a capacitor on IMAX to VCC. LR: If this pin is held high and a fault occurs, the timer will be prevented from resetting the fault latch when CT is discharged below the reset comparator threshold. The part will not retry until this pin is brought to a logic low or a power-on-reset occurs. Pulling this pin low before the reset time is reached will not clear the fault until the reset time is reached. Floating or holding this pin low will result in the part repeatedly trying to reset itself if a fault oc- curs. OUT: Output drive to the MOSFET pass element. Inter- nal clamping ensures that the maximum VGS drive is 15V. OSC, OSCB: Complementary output drivers for interme- diate charge pump stages. A 0.01 µF capacitor should be placed between OSC and PMP, and OSCB and PMPB. PLIM: This feature ensures that the average MOSFET power dissipation is controlled. A resistor is connected from this pin to VCC. Current will flow into PLIM which adds to the fault timer charge current, reducing the duty cycle from the typical 3% level. When IPL >> 100 µA then the average MOSFET power dissipation is given by: PFET_AVG = IMAX • 3 • 10 –6 •R PL. PMP, PMPB: Complementary pins which couple charge pump capacitors to internal diodes and are used to pro- vide charge to the reservoir capacitor tied to VPUMP. Typical capacitor values used are 0.01 µF. REF: –2V reference with respect to VCC used to pro- gram the IMAX pin voltage. A 0.1 µF ceramic or tantalum capacitor MUST be tied between this pin and VCC to en- sure proper operation of the chip. SD: When this TTL compatible input is brought to a logic low, the output of the linear amplifier is driven low, FAULT is pulled low and the IC is put into a low power mode. The ABSOLUTE maximum voltage that can be placed on this pin is 12V. ELECTRICAL CHARACTERISTICS: Unless otherwise specified, TA = 0°C to 70°C for the UC3914, –40°C to 85°C for the UC2914, and –55°C to 125°C for the UC1914. VCC = 12V, VPUMP =VPUMP(max), SD = 5V, CP1 = CP2 = CPUMP = 0.01 µF. TA =TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS Latch Section LR Threshold High to Low 0.6 1.4 2.0 V Input Current LR = 5V 500 750 µA Power Limiting Section Duty Cycle Control In Fault, IPLIM = 200 µA 0.6 1.3 2.0 % In Fault, IPLIM = 3mA 0.05 0.12 0.20 % Overload Section Delay to Output (Note 1) 500 1250 ns Threshold Respect to IMAX –250 –200 –150 mV Note 1: Guaranteed by design. Not 100% tested in production. Note 2: A mathematical averaging is used to determine this value. See Application Section for more information. |
Аналогичный номер детали - UC1914 |
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Аналогичное описание - UC1914 |
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