Datasheet LT8697 (Analog Devices) - 9

LT8697
PIN FUNCTIONS SYNC (Pin 1):
External Clock Synchronization Input.
PGND (Pins 7, 8):
Power Switch Ground. These pins are Tie to a clock source for synchronization to an external the return path of the internal bottom side power switch frequency and forced continuous mode. Tie to INTVCC if and must be tied together. Place the negative terminal of not used. Do not float. the input capacitor as close as possible to the PGND pins.
TR/SS (Pin 2):
Output Tracking and Soft-Start Pin. This
NC (Pins 9-12):
No Connect. These pins are floating and pin allows user control of output voltage ramp rate during are not connected to the LT8697. Tie these pins to the start-up. A TR/SS voltage below 0.97V forces the LT8697 same copper as the exposed pad. See Figure 8. to regulate VUSB5V to 5 times the TR/SS voltage. When
SW (Pins 13, 14, 15):
The SW pins are the outputs of the TR/SS is above 0.97V, the tracking function is disabled internal power switches. Tie these pins together and con- and the internal reference resumes control of the error nect them to the inductor and boost capacitor. This node amplifier. An internal 2.2µA pull-up current from INTVCC should be kept small on the PCB for good performance. on this pin allows a capacitor to program output voltage Do not drive these pins above V slew rate. This pin is pulled to ground when EN/UV is low, IN. during thermal shutdown and when VIN below its under-
BST (Pin 16):
This pin is used to provide a drive voltage, voltage lockout threshold; use a series resistor of at least higher than the input voltage, to the topside power switch. 10k if driving from a low impedance output. Place a 0.1µF boost capacitor between this pin and SW as close as possible to the LT8697 IC.
RT (Pin 3):
Tie a resistor between RT and ground to set the switching frequency.
INTVCC (Pin 17):
Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are powered
EN/UV (Pin 4):
The LT8697 is shut down when this pin from this voltage. The INTV is low and active when this pin is high. The hysteretic CC maximum output current is 20mA. INTV threshold voltage is 1.00V going up and 0.96V when going CC current will be supplied from SYS if V down. Tie to V SYS > 3.1V, otherwise current will be drawn from VIN. IN if the shutdown feature is not used. An Decouple this pin to power ground with at least a 1µF low external resistor divider from VIN can be used to program ESR ceramic capacitor. Do not load the INTV a V CC pin with IN threshold below which the LT8697 will shut down. external circuitry.
VIN (Pins 5, 6):
The VIN pins supply current to the LT8697
SYS (Pin 18):
The internal regulator will draw current internal circuitry and to the internal topside power switch. from SYS instead of V These pins must be tied together and be locally bypassed. IN when SYS is tied to a voltage higher than 3.3V. The SYS pin must be tied to the side of Place the positive terminal of the input capacitor as close the inductor opposite the SW pin and must be bypassed as possible to the VIN pins, and the negative terminal as by the output capacitor. SYS is also the secondary input close as possible to the PGND pins. to the error amp and regulates to a maximum of 5.8V. 8697fb For more information www.linear.com/LT8697 9 Document Outline Features Applications Typical Application Absolute Maximum Ratings Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts