Datasheet LT3477 (Analog Devices) - 6

LT3477
pin FuncTions (QFN/TSSOP) NC (Pins 1, 2, 20/Pins 18, 19, 20):
No Connect Pin. Okay linearly. If IADJ2 is tied to higher than 650mV, the default to connect to ground or VIN, or to float. current sense voltage is 100mV. If current sense ampli-
V
fier 2 is not used, always tie IADJ2 to higher than 650mV.
IN (Pin 3/Pin 1):
Input Supply. Must be locally bypassed. Powers the internal control circuitry.
IADJ1 (Pin 12/Pin 10):
First Current Sense Adjustment.
R
Setting I
T (Pin 4/Pin 2):
Timing Resistor Pin. Adjusts the switch- ADJ1 to be less than 625mV leads to adjustment ing frequency. Connect a 17.2k resistor between R of the sensed voltage of the first current sense amplifier T and GND for a 1MHz switching frequency. Do not leave this pin linearly. If IADJ1 is tied to higher than 650mV, the default open. See Table 4 for additional R current sense voltage is 100mV. If current sense ampli- T values and switching frequencies. fier 1 is not used, always tie IADJ1 to higher than 650mV.
SHDN (Pin 5/Pin 3):
Shutdown. Tie to 2V or greater to
ISP2 (Pin 13/Pin 11):
Second Current Sense (+) Pin. The enable the device. Tie below 0.3V to turn off the device. noninverting input to the second current sense amplifier. Connect to I
SS (Pin 6/Pin 4):
Soft-Start. Place a soft-start capacitor SN2 if not used. here. Leave floating if not in use.
ISN2 (Pin 14/Pin 12):
Second Current Sense (–) Pin. The inverting input to the second current sense amplifier. Con-
VC (Pin 7/Pin 5):
Compensation Pin for Error Amplifier. nect to I Connect a series RC from this pin to GND. Typical values SP2 if not used. are 1kΩ and 4.7nF.
ISP1 (Pin 15/Pin 13):
First Current Sense (+) Pin. The noninverting input to the first current sense amplifier.
FBN (Pin 8/Pin 6):
The Inverting Input to the Error Ampli- Connect to I fier. Connect resistive divider tap here for positive output SN1 if not used. voltage.
ISN1 (Pin 16/Pin 14):
First Current Sense (–) Pin. The in-
FBP (Pin 9/Pin 7):
The Noninverting Input to the Error verting input to the first current sense amplifier. Connect Amplifier. Connect resistive divider tap here for negative to ISP1 if not used. output voltage.
GND (Pins 17/Pin 15):
Ground. Tie directly to local
V
ground plane.
REF (Pin 10/Pin 8):
Bandgap Voltage Reference. Internally set to 1.235V. Connect this pin to FBP if generating a posi-
SW (Pins 18, 19/Pins 16, 17):
Switch Pins. Collector of tive output or to an external resistor divider if generating the internal NPN power switch. Connect the inductor and a negative voltage. This pin can provide up to 100µA of diode here and minimize the metal trace area connected current and can be locally bypassed with a 100pF capacitor. to this pin to minimize electromagnetic interference.
IADJ2 (Pin 11/Pin 9):
Second Current Sense Adjustment.
Exposed Pad (Pin 21/Pin 21):
Power Ground. Must be Setting IADJ2 to be less than 625mV leads to adjustment of soldered to PCB ground for electrical contact and rated the sensed voltage of the second current sense amplifier thermal performance. 3477fd 6 For more information www.linear.com/LT3477 Document Outline Description Typical Application Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Pin Functions Package Description Typical Application Related Parts