LT8650SPJVPBF datasheet(11/34 Pages) AD

11 / 34 page

LT8650SP

Rev. B

For more information www.analog.com

PIN FUNCTIONS

RT (Pin 1): A resistor is tied between RT and ground to

set the switching frequency.

GND (Pins 2, 10, Exposed Pad Pins 33–38): LT8650SP

System Ground. Connect these pins to the system ground

and the board ground plane. Place the negative terminal of

the input capacitors as close to the GND pins as possible.

The exposed pad must be soldered to the PCB in order to

lower the thermal resistance.

VIN1 (Pins 4, 5): The VIN1 pin supplies current to the

LT8650SP internal circuitry and to the internal top side

power switch of channel 1. This pin must be locally

bypassed. Be sure to place the positive terminal of the

input capacitor as close as possible to the VIN1 pin, and

the negative capacitor terminal as close as possible to the

GND pins. VIN1 must be 3V or higher for the LT8650SP

to operate.

VIN2 (Pins 7, 8): The VIN2 pin supplies current to the in-

ternal top side power switch of channel 2. This pin must

be locally bypassed. Be sure to place the positive terminal

of the input capacitor as close as possible to the VIN2 pin,

and the negative capacitor terminal as close as possible

to the GND pins. This input is capable of operating from

a different supply than VIN1. VIN1 must be present to run

channel 2.

EN/UV1 (Pin 11): Channel 1 of the LT8650SP is shut down

when this pin is low and active when this pin is high. The

hysteretic threshold voltage is 0.77V going up and 0.74V

going down. Tie to VIN1 if the shutdown feature is not

used. An external resistor divider from VIN1 can be used

to program a VIN threshold below which channel 1 of the

LT8650SP will shut down. Do not float this pin.

EN/UV2 (Pin 12): Channel 2 of the LT8650SP is shut down

when this pin is low and active when this pin is high. The

hysteretic threshold voltage is 0.77V going up and 0.74V

going down. Tie to VIN2 if shutdown feature is not used. An

external resistor divider from VIN2 can be used to program

a VIN threshold below which channel 2 of the LT8650SP

will shut down. Do not float this pin.

TEMP (Pin 13): Temperature Output Pin. This pin outputs

a voltage proportional to junction temperature. The pin is

250mV for 25°C and has a slope of 9.5mV/°C. The TEMP

pincanreportahigherthanactualtemperatureathighload

currents on channel 1, particularly at high temperature,

high VIN, and high inductor current ripple. For this reason,

the TEMP pin should not be used for active monitoring

or servo loops. See the Applications Information section

for more information.

PG1 (Pin 14): The PG1 pin is the open-drain output of an

internal comparator. PG1 remains low until the FB1 pin

is within ±7.5% of the final regulation voltage, and there

are no fault conditions. PG1 is pulled low during VIN1

UVLO, VCC UVLO, Thermal Shutdown, or when the EN/

UV1 pin is low.

PG2 (Pin 15): The PG2 pin is the open-drain output of an

internal comparator. PG2 remains low until the FB2 pin

is within ±7.5% of the final regulation voltage, and there

are no fault conditions. PG2 is pulled low during VIN1

UVLO, VCC UVLO, Thermal Shutdown, or when the EN/

UV2 pin is low.

SYNC (Pin 16): External Clock Synchronization Input.

Ground this pin for low ripple Burst Mode operation at

low output loads. Apply a DC voltage of 2.8V to 4V or tie

to VCC for forced continuous mode with spread spectrum

modulation. Float the SYNC pin for forced continuous

mode without spread spectrum modulation. Apply a clock

source to the SYNC pin for synchronization to an external

frequency. The LT8650SP will be in forced continuous

mode when an external frequency is applied.

CLKOUT(Pin17):Inforcedcontinuousmode,theCLKOUT

pin provides a 50% duty cycle square wave 90 degrees

out of phase with channel 1. This allows synchronization

with other regulators with up to four phases. When an

external clock is applied to the SYNC pin, the CLKOUT pin

will output a waveform with the same phase, duty cycle,

and frequency as the SYNC waveform. In burst mode,

the CLKOUT pin will be low. Float this pin if the CLKOUT

function is not used.

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