Datasheet LT3471 (Analog Devices) - 4

LT3471
TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency Peak Switch Current Start-Up Waveform vs Temperature vs SHDN/SS Voltage (Figure 2 Circuit)
1.50 2.0 TA = 25°C 1.45 1.8 ISUPPLY 1A/DIV 1.40 1.6 V 1.35 1.4 OUT1 2V/DIV 1.30 1.2 VOUT2 1.25 1.0 5V/DIV 1.20 0.8 CONTROL 1 AND 2 FREQUENCY (MHz) 1.15 SWITCH CURRENT (A) 0.6 5V/DIV 1.10 0.4 0.5ms/DIV 3471 G09 1.05 0.2 1.00 0 –50 –25 0 25 50 75 100 125 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2.0 TEMPERATURE (°C) VSHDN/SS (V) 3471 G07 3471 G08
PIN FUNCTIONS FB1N (Pin 1):
Negative Feedback Pin for Switcher 1. and minimize the metal trace area connected to this pin Connect resistive divider tap here. Minimize trace area at to minimize EMI. FB1N. Set VOUT = VFB1P(1 + R1/R2), or connect to ground
SHDN/SS2 (Pin 7):
Shutdown and Soft-Start Pin. Tie to for inverting topologies. 1.8V or more to enable device. Ground to shut down. Soft-
FB1P (Pin 2):
Positive Feedback Pin for Switcher 1. Connect start function is provided when the voltage at this pin is either to VREF or a divided down version of VREF, or connect ramped slowly to 1.8V with an external RC circuit. to a resistive divider tap for inverting topologies.
VIN (Pin 8):
Input Supply. Must be locally bypassed.
VREF (Pin 3):
1.00V Reference Pin. Can supply up to
SHDN/SS1 (Pin 9):
Same as SHDN/SS2 but for Switcher 1. 1mA of current. Do not pull this pin high. Must be locally Note: taking either SHDN/SS pin high will enable the part. bypassed with no less than 0.01μF and no more than 1μF. Each switcher is individually enabled with its respective A 0.1μF ceramic capacitor is recommended. Use this pin SHDN/SS pin. as the positive feedback reference or connect a resistor divider here for a smaller reference voltage.
SW1 (Pin 10):
Same as SW2 but for Switcher 1.
FB2P (Pin 4):
Same as FB1P but for Switcher 2.
Exposed Pad (Pin 11):
Ground. Connect directly to local ground plane. This ground plane also serves as a heat
FB2N (Pin 5):
Same as FB1N but for Switcher 2. sink for optimal thermal performance.
SW2 (Pin 6):
Switch Pin for Switcher 2 (Collector of in- ternal NPN power switch). Connect inductor/diode here 3471fb 4