LT8602 datasheet(16/38 Pages) LINER

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LT8603

8603f

For more information www.linear.com/LT8603

OPERATION

Multiphase Switching

The oscillator generates two clock signals 180° out of

phase with each other. Channels 1 and 3 operate from

CLK1, while Channels 2 and 4 operate from CLK2. The

clock for Channel 4 may be selected as either a ÷1,

÷2 or ÷5 version of CLK2 using the FSEL4A and FSEL4B

pins. Regardless of the divide ratio chosen, the Channel 4

clock edges remain aligned to the CLK2 edges.

Since a buck regulator only draws input current during the

top switch on cycle, multiphase operation reduces peak

input current and doubles the input current frequency.

These effects reduce input current ripple and reduce the

input capacitance required.

Undervoltage Lockout

The EN/UVLO pin is used to put the LT8603 in shutdown,

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

1.2V threshold of the EN/UVLO pin provides a program-

mable VIN undervoltage lockout through an external resis-

tor divider tied to the EN/UVLO pin. A 50mV hysteresis

voltage on the EN/UVLO pin prevents switching noise

from inadvertently shutting down the LT8603.

Power Good Comparators

Channels 1, 2 and 3 have power good comparators that

trip when the feedback pin is more than 8% above or

below its reference voltage. Channel 4 has a power good

comparator that indicates when the output voltage is more

than 8% below its reference. The PG output pins are open-

drain and pulled low when the corresponding output is out

of regulation. The PG outputs are not valid until INTVCC

rises to 2.7V.

Power-On Reset Timer

The LT8603 includes a power-on reset timer. The

power-on reset timeout period is adjustable using an

external capacitor on the CPOR pin as described in the

Applications Information section. The timer is initiated

when the POREN pin is higher than 1.2V. The output of

the POR timer, the RST pin, is an open-drain output with

a weak internal pull-up of 100k to approximately 2V. RST

is held low until the expiration of the POR timer. The RST

pin is only valid when the LT8603 is enabled and INTVCC

is above 2.7V.

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