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LTC3786 Datasheet(PDF) 9 Page - Linear Technology |
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LTC3786 Datasheet(HTML) 9 Page - Linear Technology |
9 / 36 page LTC3787 9 3787fc TYPICAL PERFORMANCE CHARACTERISTICS PIN FUNCTIONS FREQ (Pin 1/Pin 4): Frequency Control Pin for the Internal VCO. Connecting the pin to GND forces the VCO to a fixed low frequency of 350kHz. Connecting the pin to INTVCC forces the VCO to a fixed high frequency of 535kHz. The frequency can be programmed from 50kHz to 900kHz by connecting a resistor from the FREQ pin to GND. The resistor and an internal 20μA source current create a volt- age used by the internal oscillator to set the frequency. Alternatively, this pin can be driven with a DC voltage to vary the frequency of the internal oscillator. PHASMD (Pin 2/Pin 5): This pin can be floated, tied to SGND, or tied to INTVCC to program the phase relationship between the rising edges of BG1 and BG2, as well as the phase relationship between BG1 and CLKOUT. CLKOUT (Pin 3/Pin 6): A Digital Output Used for Daisy- chaining Multiple LTC3787 ICs in Multiphase Systems. The PHASMD pin voltage controls the relationship between BG1 and CLKOUT. This pin swings between SGND and INTVCC. PLLIN/MODE (Pin 4/Pin 7): External Synchronization Input to Phase Detector and Forced Continuous Mode Input. When an external clock is applied to this pin, it will force the controller into forced continuous mode of operation and the phase-locked loop will force the rising BG1 signal to be synchronized with the rising edge of the external clock. When not synchronizing to an external clock, this input determines how the LTC3787 operates at light loads. Pulling this pin to ground selects Burst Mode operation. An internal 100k resistor to ground also invokes Burst Mode operation when the pin is floated. Tying this pin to INTVCC forces continuous inductor current operation. Tying this pin to a voltage greater than 1.2V and less than INTVCC – 1.3V selects pulse-skipping operation. This can be done by adding a 100k resistor between the PLLIN/ MODE pin and INTVCC. SGND (Pin 5/Pin 8): Signal Ground. All small-signal components and compensation components should connect to this ground, which in turn connects to PGND at a single point. RUN (Pin 6/Pin 9): Run Control Input. Forcing this pin below 1.28V shuts down the controller. Forcing this pin below 0.7V shuts down the entire LTC3787, reducing quiescent current to approximately 8μA. An external resistor divider connected to VIN can set the threshold for converter operation. Once running, a 4.5μA current is sourced from the RUN pin allowing the user to program hysteresis using the resistor values. Maximum Current Sense Threshold vs Duty Cycle Charge Pump Charging Current vs Operating Frequency DUTY CYCLE (%) 0 80 100 70 60 40 20 40 10 90 30 50 80 60 100 20 0 120 3787 G25 ILIM = INTVCC ILIM = FLOAT ILIM = GND (QFN/SSOP) Charge Pump Charging Current vs Switch Voltage SWITCH VOLTAGE (V) 5 0 20 30 80 50 15 25 30 10 60 70 40 10 20 35 40 3787 G27 FREQ = INTVCC FREQ = GND OPERATING FREQUENCY (kHz) 50 0 20 30 80 50 250 450 550 10 60 70 40 150 350 650 750 3787 G26 T = 130°C T = 155°C T = 25°C T = – 45°C T = – 60°C |
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