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LT8610

42V, 2.5A Synchronous Step-Down Regulator with 2.5µA Quiescent Current

Linear Technology 

LT8610

OPERATION

The LT8610 is a monolithic, constant frequency, current

mode step-down DC/DC converter. An oscillator, with

frequency set using a resistor on the RT pin, turns on

the internal top power switch at the beginning of each

clock cycle. Current in the inductor then increases until

the top switch current comparator trips and turns off the

top power switch. The peak inductor current at which

the top switch turns off is controlled by the voltage on

the internal VC node. The error amplifier servos the VC

node by comparing the voltage on the VFB pin with an

internal 0.97V reference. When the load current increases

it causes a reduction in the feedback voltage relative to

the reference leading the error amplifier to raise the VC

voltage until the average inductor current matches the new

load current. When the top power switch turns off, the

synchronous power switch turns on until the next clock

cycle begins or inductor current falls to zero. If overload

conditions result in more than 3.3A flowing through the

bottom switch, the next clock cycle will be delayed until

switch current returns to a safe level.

If the EN/UV pin is low, the LT8610 is shut down and

draws 1µA from the input. When the EN/UV pin is above

1V, the switching regulator will become active.

To optimize efficiency at light loads, the LT8610 operates

in Burst Mode operation in light load situations. Between

bursts, all circuitry associated with controlling the output

switch is shut down, reducing the input supply current to

1.7μA. In a typical application, 2.5μA will be consumed

from the input supply when regulating with no load. The

SYNC pin is tied low to use Burst Mode operation and can

be tied to a logic high to use pulse-skipping mode. If a

clock is applied to the SYNC pin the part will synchronize to

an external clock frequency and operate in pulse-skipping

mode. While in pulse-skipping mode the oscillator operates

continuously and positive SW transitions are aligned to

the clock. During light loads, switch pulses are skipped

to regulate the output and the quiescent current will be

several hundred µA.

To improve efficiency across all loads, supply current to

internal circuitry can be sourced from the BIAS pin when

biased at 3.3V or above. Else, the internal circuitry will draw

current from VIN. The BIAS pin should be connected to

VOUT if the LT8610 output is programmed at 3.3V or above.

Comparators monitoring the FB pin voltage will pull the

PG pin low if the output voltage varies more than ±9%

(typical) from the set point, or if a fault condition is present.

The oscillator reduces the LT8610’s operating frequency

when the voltage at the FB pin is low. This frequency

foldback helps to control the inductor current when the

output voltage is lower than the programmed value which

occurs during start-up or overcurrent conditions. When

a clock is applied to the SYNC pin or the SYNC pin is

held DC high, the frequency foldback is disabled and the

switching frequency will slow down only during overcur-

rent conditions.

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For more information www.linear.com/LT8610

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