Datasheet LT8631 (Analog Devices) - 9

LT8631
PIN FUNCTIONS VIN (Pin 1):
The VIN pin powers the internal control circuitry pin. The voltage ramp rate on the TR/SS pin determines and is monitored by an undervoltage lockout comparator. the output voltage ramp rate. This pin can also be used The VIN pin is also connected to the drain of the on chip for voltage tracking. Do not leave this pin floating. power switch. The VIN pin has high dI/dt edges and must
FB (Pin 11):
The FB pin is the negative input to the er- be decoupled to the GND pin of the device. The input ror amplifier. The output switches to regulate this pin to decouple capacitor should be placed as close as possible 0.808V with respect to the GND pin. to the VIN and GND pins.
V EN/UV (Pin 3):
The EN/UV pin is used to enable the LT8631
OUT (Pin 12):
The VOUT pin is the output to the internal sense resistor that measures current flowing in the in- or to program the undervoltage lockout threshold with ex- ductor. Connect the output capacitor from the V ternal resistors. The LT8631 is in shutdown mode( I OUT pin Q < 5µA) to the GND pin. when the EN/UV pin voltage is below 1.19V and active mode when the voltage exceeds 1.19V. Tie EN/UV to the
NC13 (Pin 13):
No Internal Connection. Leave this pin VIN pin if the EN/UV feature isn’t required. open or connect to GND.
PG (Pin 5):
The PG pin is an open drain output that sinks
IND (Pin 14):
The IND pin is the input to the internal sense current when the feedback voltage deviates from the regula- resistor that measures current flowing in the inductor. tion point by ±7.5%. The PG pin has 1.9% of hysteresis.
NC15 (Pin 15):
No Internal Connection. Leave this pin
NC6 (Pin 6):
No Internal Connection. Leave this pin open open or connect to GND. or connect to GND.
INTVCC (Pin 16):
The INTVCC pin is the bypass pin for the
SYNC/MODE (Pin 7):
The voltage present at the SYNC/ internal 3V regulator. Connect a 2.2µF bypass capacitor MODE pin determines the LT8631 operating mode. Ground from the INTVCC pin to the GND pin. Do not load the INTVCC this pin for low ripple Burst Mode operation at low output pin with external circuitry. loads. Apply a DC voltage greater than the SYNC/MODE
BST (Pin 18):
The BST pin is used to provide a drive threshold for pulse-skipping operation at low output loads. voltage, higher than the V The LT8631 will synchronize it’s switching frequency to an IN voltage, to the topside power switch. Place a 0.1µF capacitor between the BST and SW external clock applied to the SYNC/MODE pin. The external pins as close as possible to the device. clock signal must have a duty cycle between 20% and 80% and be within the specified frequency range. The LT8631
SW (Pin 20):
The SW pin is the output of the internal power will operate in pulse-skipping mode when the SYNC/MODE switches. Place the inductor and BST capacitor as close pin is driven with an external clock. as possible to keep the SW PCB trace short.
RT (Pin 8):
A resistor with a value between 8.66k and
GND (Exposed Pad Pin 21):
The exposed pad GND pin 187k must be connected between the RT pin and the GND is the ONLY GROUND CONNECTION for the device. The pin. The R exposed pad should be soldered to a large copper area T resistor sets the switching frequency. Do not leave this pin floating. to reduce thermal resistance. The GND pin also serves as small signal ground. For ideal operation all small signal
NC9 (Pin 9):
No Internal Connection. Leave this pin open ground paths should connect to the GND pin at a single or connect to GND. point avoiding any high current ground returns.
TR/SS (Pin 10):
A capacitor with a minimum value of 100pF must be connected between the TR/SS pin and the GND 8631fb For more information www.linear.com/LT8631 9