Datasheet LT3958 (Analog Devices) - 8

LT3958
pin FuncTions NC (Pins 1, 2, 10, 35, 36):
No Internal Connection. Leave
INTVCC (Pin 28):
Regulated Supply for Internal Loads these pins open or connect them to the adjacent pins. and Gate Driver. Supplied from VIN and regulated to
SENSE2 (Pin 3):
The Current Sense Input for the Control 7.2V (typical). INTVCC must be bypassed to SGND with a Loop. Connect this pin to SENSE1 pin directly or through minimum of 4.7µF capacitor placed close to pin. INTVCC a low pass filter (connect this pin to SENSE1 pin through can be connected directly to VIN, if VIN is less than 11.5V. a resistor, and to SGND through a capacitor). INTVCC can also be connected to a power supply whose voltage is higher than 7.5V, and lower than VIN, provided
SGND (Pins 4, 23, 24, Exposed Pad Pin 37):
Signal that supply does not exceed 11.5V. Ground. All small-signal components should connect to this ground. SGND is connected to GND inside the IC to
VC (Pin 30):
Error Amplifier Compensation Pin. Used to ensure Kelvin connection for the internal switch current stabilize the voltage loop with an external RC network. sensing. Do not connect SGND and GND externally. Place compensation components between the VC pin and SGND.
SENSE1 (Pin 6):
The Current Sense Output of the Inter- nal N-channel MOSFET. Connect this pin to SENSE2 pin
FBX (Pin 31):
Positive and Negative Feedback Pin. Re- directly or through a low pass filter (connect this pin to ceives the feedback voltage from the external resistor SENSE1 pin through a resistor, then connect SENSE2 to divider between the output and SGND. Also modulates the SGND through a capacitor). switching frequency during start-up and fault conditions when FBX is close to SGND.
SW (Pins 8,9,20,21, Exposed Pad Pin 38):
Drain of Internal Power N-channel MOSFET.
SS (Pin 32):
Soft-Start Pin. This pin modulates compen- sation pin voltage (VC) clamp. The soft-start interval is
GND (Pins 12,13,14,15,16,17):
Ground. These pins con- set with an external capacitor between SS pin and SGND. nect to the source terminal of internal power N-channel The pin has a 10µA (typical) pull-up current source to MOSFET through an internal sense resistor. GND is con- an internal 2.5V rail. The soft-start pin is reset to SGND nected to SGND inside the IC to ensure Kelvin connection by an undervoltage condition at EN/UVLO, an INTVCC for the internal switch current sensing. Do not connect undervoltage or overvoltage condition or an internal GND and SGND externally. thermal lockout.
EN/UVLO (Pin 25):
Shutdown and Undervoltage Detect
RT (Pin 33):
Switching Frequency Adjustment Pin. Set Pin. An accurate 1.22V (nominal) falling threshold with the frequency using a resistor to SGND. Do not leave this externally programmable hysteresis detects when power pin open. is okay to enable switching. Rising hysteresis is generated by the external resistor divider and an accurate internal
SYNC (Pin 34):
Frequency Synchronization Pin. Used to 2µA pull-down current. An undervoltage condition resets synchronize the switching frequency to an outside clock. sort-start. Tie to 0.4V, or less, to disable the device and If this feature is used, an RT resistor should be chosen reduce V to program a switching frequency 20% slower than the IN quiescent current below 1µA. SYNC pulse frequency. Tie the SYNC pin to SGND if this
VIN (Pin 27):
Input Supply Pin. VIN pin can be locally feature is not used. SYNC is ignored when FBX is close bypassed with a capacitor to GND (not SGND). to SGND. 3958fa 8 For more information www.linear.com/LT3958 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Revision History Typical Applications Related Parts