Datasheet LT8607, LT8607B (Analog Devices) - 9

LT8607/LT8607B
PIN FUNCTIONS BST:
This pin is used to provide a drive voltage, higher
TR/SS (MSOP Only):
Output Tracking and Soft-Start Pin. than the input voltage, to the topside power switch. Place This pin allows user control of output voltage ramp rate a 0.1µF boost capacitor as close as possible to the IC. Do during start-up. A TR/SS voltage below 0.778V forces the not place a resistor in series with this pin. LT8607 to regulate the FB pin to equal the TR/SS pin volt-
SW:
The SW pin is the output of the internal power age. The LT8607-5 will track the TR/SS pin voltage based switches. Connect this pin to the inductor and boost on a factor set by the internal resistor divider. The part capacitor. This node should be kept small on the PCB for will track to 6.43 times the TR/SS voltage. When TR/SS good performance. is above 0.778V, the tracking function is disabled and the internal reference resumes control of the error amplifier.
INTVCC:
Internal 3.5V Regulator Bypass Pin. The internal An internal 2µA pull-up current from INTVCC on this pin power drivers and control circuits are powered from this allows a capacitor to program output voltage slew rate. voltage. INTVCC max output current is 20mA. Voltage on This pin is pulled to ground with a 300Ω MOSFET dur- INTVCC will vary between 2.8V and 3.5V. Decouple this ing shutdown and fault conditions; use a series resistor pin to power ground with at least a 1µF low ESR ceramic if driving from a low impedance output. There is no TR/ capacitor. Do not load the INTVCC pin with external circuitry. SS pin on the LT8607 or LT8607B DFN and the node is
RT:
A resistor is tied between RT and ground to set the internally floated. switching frequency. When synchronizing, the RT resistor
PG:
The PG pin is the open-drain output of an internal should be chosen to set the LT8607 switching frequency comparator. PG remains low until the FB pin is within to equal or below the lowest synchronization input. ±8.5% of the final regulation voltage, and there are no
SYNC (MSOP Only):
External Clock Synchronization fault conditions. PG is valid when VIN is above 3.2V and Input. Ground this pin for low ripple Burst Mode operation when EN/UV is high. PG is pulled low when VIN is above at low output loads. Tie to a clock source for synchroni- 3.2V and EN/UV is low. If VIN is near zero, PG will be high zation to an external frequency. Leave floating for pulse- impedance. skipping mode with no spread spectrum modulation. Tie
VIN:
The VIN pin supplies current to the LT8607 internal to INTVCC or tie to a voltage between 3.2V and 5.0V for circuitry and to the internal topside power switch. This pin pulse-skipping mode with spread spectrum modulation. must be locally bypassed. Be sure to place the positive When in pulse-skipping mode, the IQ regulating no load terminal of the input capacitor as close as possible to the will increase to several mA. There is no SYNC pin on VIN pins, and the negative capacitor terminal as close as the LT8607 DFN package. The LT8607 DFN internal y possible to the GND pins. ties SYNC to ground. The LT8607B package internal y floats SYNC.
EN/UV:
The LT8607 is shut down when this pin is low and active when this pin is high. The hysteretic threshold volt-
FB (LT8607/LT8607B Only):
The LT8607 regulates the age is 1.05V going up and 1.00V going down. Tie to VIN FB pin to 0.778V. Connect the feedback resistor divider if the shutdown feature is not used. An external resistor tap to this pin. divider from VIN can be used to program a VIN threshold
V
below which the LT8607 will shut down.
OUT (LT8607-5 Only):
The LT8607-5 regulates the VOUT pin to 5V. This pin connects to a 6.6MΩ internal divider.
GND:
Exposed Pad Pin. The exposed pad must be con- nected to the negative terminal of the input capaci- tor and soldered to the PCB in order to lower the thermal resistance. Rev. D For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts