LT8608 datasheet(8/24 Pages) LINER

8 / 24 page

LT8608/LT8608B

Rev C

For more information www.analog.com

PIN FUNCTIONS

BST: This pin is used to provide a drive voltage, higher

than the input voltage, to the topside power switch. Place

a 0.1µF boost capacitor as close as possible to the IC. Do

not place a resistor in series with this pin.

SW: The SW pin is the output of the internal power

switches. Connect this pin to the inductor and boost

capacitor. This node should be kept small on the PCB for

good performance.

INTVCC: Internal 3.5V Regulator Bypass Pin. The internal

power drivers and control circuits are powered from this

voltage. INTVCC max output current is 20mA. Voltage on

INTVCC will vary between 2.8V and 3.5V. Decouple this

pin to power ground with at least a 1μF low ESR ceramic

capacitor.DonotloadtheINTVCCpinwithexternalcircuitry.

RT: A resistor is tied between RT and ground to set the

switching frequency. When synchronizing, the RT resistor

should be chosen to set the LT8608 switching frequency

equal to or below the lowest synchronization input.

SYNC(MSOPOnly):ExternalClockSynchronizationInput.

Ground this pin for low ripple Burst Mode operation at low

output loads. Tie to a clock source for synchronization to

an external frequency. Leave floating for pulse-skipping

mode with no spread spectrum modulation. Tie to INTVCC

ortietoavoltagebetween3.2Vand5.0Vforpulse-skipping

mode with spread spectrum modulation. When in pulse-

skipping mode, the IQ will increase to several mA. There

is no SYNC pin in the LT8608 DFN package. The LT8608

DFN package internally ties SYNC to ground. The LT8608B

DFN package internally floats SYNC.

FB: The LT8608 regulates the FB pin to 0.778V. Connect

the feedback resistor divider tap to this pin.

TR/SS (MSOP Only): Output Tracking and Soft-Start Pin.

This pin allows user control of output voltage ramp rate

during start-up. A TR/SS voltage below 0.778V forces the

LT8608 to regulate the FB pin to equal the TR/SS pin volt-

age. When TR/SS is above 0.778V, the tracking function

is disabled and the internal reference resumes control of

the error amplifier. An internal 2μA pull-up current from

INTVCC on this pin allows a capacitor to program output

voltage slew rate. This pin is pulled to ground with a 300Ω

MOSFETduringshutdownandfaultconditions;useaseries

resistor if driving from a low impedance output. There is

no TR/SS pin in the LT8608 DFN or LT8608B and the node

is internally floated.

PG: The PG pin is the open-drain output of an internal

comparator. PG remains low until the FB pin is within

±8.5% of the final regulation voltage, and there are no fault

conditions. PG is valid when VIN is above 3.2V, regardless

of EN/UV pin state.

VIN: The VIN pin supplies current to the LT8608 internal

circuitry and to the internal topside power switch. This pin

must be locally bypassed. Be sure to place the positive

terminal of the input capacitor as close as possible to the

VIN pins, and the negative capacitor terminal as close as

possible to the GND pins.

EN/UV: The LT8608 is shut down when this pin is low and

active when this pin is high. The hysteretic threshold volt-

age is 1.05V going up and 1.00V going down. Tie to VIN

if the shutdown feature is not used. An external resistor

divider from VIN can be used to program a VIN threshold

below which the LT8608 will shut down.

GND: Exposed Pad Pin. The exposed pad must be con-

nected to the negative terminal of the input capacitor and

solderedtothePCBinordertolowerthethermalresistance.

LT8608 Datasheet(PDF) 8 Page - Linear Technology

LT8608 Datasheet(HTML) 8 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL