Datasheet LTC3785-1 (Analog Devices) - 5

LTC3785-1
TYPICAL PERFORMANCE CHARACTERISTICS Normalized Oscillator Frequency VFB vs Temperature vs Temperature Oscillator Frequency vs RT
1.2255 1.0 1200 1.2250 0.8 1000 1.2245 0.6 0.4 1.2240 800 0.2 1.2235 (V) 0 600 FBV 1.2230 –0.2 1.2225 400 –0.4 CHANGE FROM 25°C (%) 1.2220 –0.6 OSCILLATOR FREQUENCY (kHz) 200 1.2215 –0.8 1.2210 –1.0 0 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 20 40 60 80 100 TEMPERATURE (°C) TEMPERATURE (°C) RT (kΩ) 37851 G07 37851 G08 37851 G09
VIN Start-Up Voltage VIN Burst Quiescent Current OV and UV Thresholds vs Temperature vs Temperature vs Temperature
2.490 100 8 6 OV THRESHOLD 2.485 95 4 2 2.480 90 0 2.475 CURRENT (mA) –2 IN THRESHOLD (%) START-UP VOLTAGE (V) V IN 85 –4 V 2.470 –6 UV THRESHOLD 2.465 80 –8 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 37851 G10 37851 G11 37851 G12
PIN FUNCTIONS RUN/SS (Pin 1):
Run Control and Soft-Start Input. An
VC (Pin 2):
Error Amp Output. A frequency compensation internal 1μA charges the soft-start capacitor and will network is connected from this pin to the FB pin to compen- charge to approximately 2.5V. During a current limit fault, sate the loop. See the section Closing the Feedback Loop the soft-start capacitor will incrementally discharge. Once in the Applications Information section for guidelines. the pin drops below 1.225V the IC will enter fault mode,
FB (Pin 3):
Feedback Pin. Connect resistor divider tap turning off the outputs for 32 times the soft-start time. If here. The feedback reference voltage is typically 1.225V >5μA (at RUN/SS = 1.225V) is applied externally, the part The output voltage can be adjusted from 2.7V to 10V ac- will latch off after a fault is detected. If >40μA (at RUN/SS cording to the following formula: = 1.225V) is applied externally, current limit faults will not discharge the SS capacitor. R1+R2 VOUT = 1.225V • R2 37851fa 5