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UC1875-SP датащи(PDF) 7 Page - Texas Instruments |
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UC1875-SP датащи(HTML) 7 Page - Texas Instruments |
7 / 20 page (RAMP) (SLOPE) dV Sense Voltage = dT R x C UC1875-SP www.ti.com SLUSAQ9 – DECEMBER 2011 PIN DESCRIPTIONS CLKSYNC (bi-directional clock and synchronization pin): Used as an output, this pin provides a clock signal. As an input, this pin provides a synchronization point. In its simplest usage, multiple devices, each with their own local oscillator frequency, may be connected together by the CLOCKSYNC pin and will synchronize on the fastest oscillator. This pin may also be used to synchronize the device to an external clock, provided the external signal is of higher frequency than the local oscillator. A resistor load may be needed on this pin to minimize the clock pulse width. E/AOUT (Error Amplifier Output): This is is the gain stage for overall feedback control. Error amplifier output voltage levels below 1 volt will force 0 ° phase shift. Since the error amplifier has a relatively low current drive capability, the output may be overridden by driving with a sufficiently low impedance source. CS+ (Current Sense): The non-inverting input to the current-fault comparator whose reference is set internally to a fixed 2.5 V (separate from VREF). When the voltage at this pin exceeds 2.5 V the current-fault latch is set, the outputs are forced OFF and a SOFT-START cycle is initiated. If a constant voltage above 2.5 V is applied to this pin the outputs are disabled from switching and held in a low state until the CS+ pin is brought below 2.5 V. The outputs may begin switching at 0 degrees phase shift before the SOFTSTART pin begins to rise -- this condition will not prematurely deliver power to the load. FREQSET (Oscillator Frequency Set pin): A resistor and a capacitor from FREQSET to GND will set the oscillator frequency. DELSETA-B, DELSETC-D (Output Delay Control): The user programmed current flowing from these pins to GND set the turn-on delay for the corresponding output pair. This delay is introduced between turn-off of one switch and turn-on of another in the same leg of the bridge to provide a dead time in which the resonant switching of the external power switches takes place. Separate delays are provided for the two half-bridges to accommodate differences in the resonant capacitor charging currents. EA – (Error Amplifier Inverting Input): This is normally connected to the voltage divider resistors which sense the power supply output voltage level. EA+ (Error Amplifier Non-Inverting Input): This is normally connected to a reference voltage used for comparison with the sensed power supply output voltage level at the EA+ pin. GND (Signal Ground): All voltages are measured with respect to GND. The timing capacitor, on the FREQSET pin, any bypass capacitor on the VREF pin, bypass capacitors on VIN and the ramp capacitor, on the RAMP pin, should be connected directly to the ground plane near the signal ground pin. OUTA – OUTD (Outputs A-D): The outputs are 2 A totem-pole drivers optimized for both MOSFET gates and level-shifting transformers. The outputs operate as pairs with a nominal 50% duty-cycle. The A-B pair is intended to drive one half-bridge in the external power stage and is syncronized with the clock waveform. The C-D pair will drive the other half-bridge with switching phase shifted with respect to the A-B outputs. PWRGND (Power Ground): VC should be bypassed with a ceramic capacitor from the VC pin to the section of the ground plane that is connected to PWRGND. Any required bulk reservoir capacitor should parallel this one. Power ground and signal ground may be joined at a single point to optimize noise rejection and minimize DC drops. RAMP (Voltage Ramp): This pin is the input to the PWM comparator. Connect a capacitor from here to GND. A voltage ramp is developed at this pin with a slope: Current mode control may be achieved with a minimum amount of external circuitry, in which case this pin provides slope compensation. Because of the 1.3 V offset between the ramp input and the PWM comparator, the error amplifier output voltage can not exceed the effective ramp peak voltage and duty cycle clamping is easily achievable with appropriate values of R(SLOPE) and C(RAMP). SLOPE (Set Ramp Slope/Slope Compensation): A resistor from this pin to VCC will set the current used to generate the ramp. Connecting this resistor to the DC input line voltage will provide voltage feed-forward. Copyright © 2011, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Link(s): UC1875-SP |
Аналогичный номер детали - UC1875-SP |
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Аналогичное описание - UC1875-SP |
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