LT8602 datasheet(14/30 Pages) LINER

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LT8602

8602fb

For more information www.linear.com/LT8602

operaTion

TheLT8602isaquadchannel,constantfrequency,current

mode, monolithic buck switching regulator with power-on

reset. All channels are synchronized to a single oscillator.

Two of the channels are high voltage (up to 42V input)

while the other two are low voltage (up to 5.5V input) and

are typically powered from the high voltage buck outputs.

Start-Up

When enabled by setting the EN/UVLO voltage above its

threshold,theLT8602startschargingtheINTVCCcapacitor

fromVIN.IfBIASishigherthan3.1V,BIASsuppliescurrent

to the INTVCC regulator to reduce VIN quiescent current.

High Voltage Buck Regulators

Each high voltage channel is a synchronous buck regulator

that operates from an independent PVIN pin. The internal

top power MOSFET is turned on at the beginning of each

oscillator cycle, and turned off when the current flowing

through the top MOSFET reaches a level determined by

the error amplifier. The error amplifier measures the output

voltage through an external resistor divider tied to the FB

pin to control the peak current in the top switch. The refer-

ence of the error amplifier is determined by the lower of

the internal 1V reference and the voltage at its TRKSS pin.

While the top MOSFET is off, the bottom MOSFET is

turned on for the remainder of the oscillator cycle or

until the inductor current starts to reverse. If overload

conditions result in more than 2A (Ch 1) or 3.3A (Ch 2)

flowing through the bottom switch, the next clock cycle

will be delayed until switch current returns to a safe level.

Low Voltage Buck Regulators

Each low voltage channel is a synchronous buck regulator

that operates from an independent PVIN pin. The PVIN pins

have an undervoltage lockout set at 2.35V. Each internal

top power MOSFET is turned on at the beginning of each

oscillator cycle, and turned off when the current flowing

through the top MOSFET reaches a level determined

by the error amplifier. The error amplifier measures the

output voltage through an external resistor divider tied to

the FB pin to control the peak current in the top switch.

The reference of the error amplifier is an internal 800mV

reference. Each LV channel has a RUN pin to allow power

sequencing and an internal soft-start circuit ramps the

output voltage up in 1ms.

While the top MOSFET is off, the bottom MOSFET is turned

on for the remainder of the oscillator cycle or until the

inductor current starts to reverse. If overload conditions

resultinmorethan2.4Aflowingthroughthebottomswitch,

the next clock cycle will be delayed until switch current

returns to a safe level.

Multiphase Switching

The oscillator generates two clock signals 180° out of

phase.Channels1and3operateonCLK1,whilechannels2

and 4 operate on CLK2. Since a buck regulator only draws

input current during the top switch on cycle, multiphase

operationreducespeakinputcurrentanddoublestheinput

currentfrequency.Theseeffectsreduceinputcurrentripple

and reduce the input capacitance required.

Light Load Operation

At light load, the regulators operate in low ripple burst

mode. Low ripple burst mode shuts down most internal

circuitry between switch on cycles to conserve power

while still retaining low ripple at the output.

Undervoltage Lockout

The EN/UVLO pin is used to put the LT8602 in shutdown,

reducing the input current to less than 1μA. The accurate

1.2VthresholdoftheEN/UVLOpinallowsaprogrammable

VIN undervoltage lockout through an external resistor

divider tied to the EN/UVLO pin. A 50mV (typ) hysteresis

voltageontheEN/UVLOpinpreventsswitchingnoisefrom

inadvertently shutting down the LT8602.

LT8602 Datasheet(PDF) 14 Page - Linear Technology

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