Datasheet LT3957A (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | Boost, Flyback, SEPIC and Inverting Converter with 5A, 40V Switch |
| Pages / Page | 28 / 7 — PIN FUNCTIONS. NC (Pins 1, 2, 10, 35, 36):. INTVCC (Pin 28):. SENSE2 (Pin … |
| File Format / Size | PDF / 567 Kb |
| Document Language | English |
PIN FUNCTIONS. NC (Pins 1, 2, 10, 35, 36):. INTVCC (Pin 28):. SENSE2 (Pin 3):. SGND (Pins 4, 23, 24, Exposed Pad Pin 37):
Model Line for this Datasheet
Text Version of Document
LT3957A
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 5.2V (typical). INTV
SENSE2 (Pin 3):
The Current Sense Input for the Control CC must be bypassed to SGND with a minimum of 4.7μF capacitor placed close to pin. INTV Loop. Connect this pin to SENSE1 pin directly or through CC can be connected directly to V a low pass filter (connect this pin to SENSE1 pin through IN, if VIN is less than 8V. INTV a resistor, and to SGND through a capacitor). CC can also be connected to a power supply whose voltage is higher than 5.5V, and lower than VIN, provided
SGND (Pins 4, 23, 24, Exposed Pad Pin 37):
Signal that supply does not exceed 8V. Ground. All small-signal components should connect to
V
this ground. SGND is connected to GND inside the IC to
C (Pin 30):
Error Amplifier Compensation Pin. Used to stabilize the voltage loop with an external RC network. Place ensure Kelvin connection for the internal switch current compensation components between the V sensing. Do not connect SGND and GND externally. C pin and SGND.
FBX (Pin 31):
Positive and Negative Feedback Pin. Re-
SENSE1 (Pin 6):
The Current Sense Output of the Inter- ceives the feedback voltage from the external resistor nal N-channel MOSFET. Connect this pin to SENSE2 pin divider between the output and SGND. Also modulates the directly or through a lowpass filter (connect this pin to switching frequency during start-up and fault conditions SENSE1 pin through a resistor, then connect SENSE2 to when FBX is close to SGND. SGND through a capacitor).
SS (Pin 32):
Soft-Start Pin. This pin modulates compen-
SW (Pins 8, 9, 20, 21, Exposed Pad Pin 38):
Drain of sation pin voltage (V Internal Power N-channel MOSFET. C) clamp. The soft-start interval is set with an external capacitor between SS pin and SGND.
GND (Pins 12, 13, 14, 15, 16, 17):
Ground. These pins The pin has a 10μA (typical) pull-up current source to an connect to the source terminal of internal power N-channel internal 2.5V rail. The soft-start pin is reset to SGND by an MOSFET through an internal sense resistor. GND is con- undervoltage condition at EN/UVLO, an INTVCC undervolt- nected to SGND inside the IC to ensure Kelvin connection age or overvoltage condition or an internal thermal lockout. for the internal switch current sensing. Do not connect
RT (Pin 33):
Switching Frequency Adjustment Pin. Set GND and SGND externally. the frequency using a resistor to SGND. Do not leave this
EN/UVLO (Pin 25):
Shutdown and Undervoltage Detect pin open. Pin. An accurate 1.22V (nominal) falling threshold with
SYNC (Pin 34):
Frequency Synchronization Pin. Used to externally programmable hysteresis detects when power synchronize the switching frequency to an outside clock. is okay to enable switching. Rising hysteresis is generated If this feature is used, an R by the external resistor divider and an accurate internal T resistor should be chosen to program a switching frequency 20% slower than the 2μA pull-down current. An undervoltage condition resets SYNC pulse frequency. Tie the SYNC pin to SGND if this soft-start. Tie to 0.4V, or less, to disable the device and feature is not used. SYNC is bypassed when FBX is close reduce VIN quiescent current below 1μA. to SGND.
VIN (Pin 27):
Input Supply Pin. The VIN pin can be locally bypassed with a capacitor to GND (not SGND). 3957afa 7
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 5.2V (typical). INTV
SENSE2 (Pin 3):
The Current Sense Input for the Control CC must be bypassed to SGND with a minimum of 4.7μF capacitor placed close to pin. INTV Loop. Connect this pin to SENSE1 pin directly or through CC can be connected directly to V a low pass filter (connect this pin to SENSE1 pin through IN, if VIN is less than 8V. INTV a resistor, and to SGND through a capacitor). CC can also be connected to a power supply whose voltage is higher than 5.5V, and lower than VIN, provided
SGND (Pins 4, 23, 24, Exposed Pad Pin 37):
Signal that supply does not exceed 8V. Ground. All small-signal components should connect to
V
this ground. SGND is connected to GND inside the IC to
C (Pin 30):
Error Amplifier Compensation Pin. Used to stabilize the voltage loop with an external RC network. Place ensure Kelvin connection for the internal switch current compensation components between the V sensing. Do not connect SGND and GND externally. C pin and SGND.
FBX (Pin 31):
Positive and Negative Feedback Pin. Re-
SENSE1 (Pin 6):
The Current Sense Output of the Inter- ceives the feedback voltage from the external resistor nal N-channel MOSFET. Connect this pin to SENSE2 pin divider between the output and SGND. Also modulates the directly or through a lowpass filter (connect this pin to switching frequency during start-up and fault conditions SENSE1 pin through a resistor, then connect SENSE2 to when FBX is close to SGND. SGND through a capacitor).
SS (Pin 32):
Soft-Start Pin. This pin modulates compen-
SW (Pins 8, 9, 20, 21, Exposed Pad Pin 38):
Drain of sation pin voltage (V Internal Power N-channel MOSFET. C) clamp. The soft-start interval is set with an external capacitor between SS pin and SGND.
GND (Pins 12, 13, 14, 15, 16, 17):
Ground. These pins The pin has a 10μA (typical) pull-up current source to an connect to the source terminal of internal power N-channel internal 2.5V rail. The soft-start pin is reset to SGND by an MOSFET through an internal sense resistor. GND is con- undervoltage condition at EN/UVLO, an INTVCC undervolt- nected to SGND inside the IC to ensure Kelvin connection age or overvoltage condition or an internal thermal lockout. for the internal switch current sensing. Do not connect
RT (Pin 33):
Switching Frequency Adjustment Pin. Set GND and SGND externally. the frequency using a resistor to SGND. Do not leave this
EN/UVLO (Pin 25):
Shutdown and Undervoltage Detect pin open. Pin. An accurate 1.22V (nominal) falling threshold with
SYNC (Pin 34):
Frequency Synchronization Pin. Used to externally programmable hysteresis detects when power synchronize the switching frequency to an outside clock. is okay to enable switching. Rising hysteresis is generated If this feature is used, an R by the external resistor divider and an accurate internal T resistor should be chosen to program a switching frequency 20% slower than the 2μA pull-down current. An undervoltage condition resets SYNC pulse frequency. Tie the SYNC pin to SGND if this soft-start. Tie to 0.4V, or less, to disable the device and feature is not used. SYNC is bypassed when FBX is close reduce VIN quiescent current below 1μA. to SGND.
VIN (Pin 27):
Input Supply Pin. The VIN pin can be locally bypassed with a capacitor to GND (not SGND). 3957afa 7
