LTM8048 datasheet(9/22 Pages) LINER

9 / 22 page

LTM8045

8045fa

For more information www.linear.com/8045

PIN FUNCTIONS

VOUT– (Bank 1): VOUT– is the negative output of the

LTM8045. Apply an external capacitor between VOUT+and

VOUT–. Tie this net to GND to configure the LTM8045 as

a positive output SEPIC regulator.

VOUT+ (Bank 2): VOUT+ is the positive output of the

LTM8045. Apply an external capacitor between VOUT+ and

VOUT–. Tie this net to GND to configure the LTM8045 as

a negative output inverting regulator.

GND (Bank 3): Tie these GND pins to a local ground plane

below the LTM8045 and the circuit components. GND

MUST BE CONNECTED EITHER TO VOUT+ OR VOUT– FOR

PROPER OPERATION. In most applications, the bulk of

the heat flow out of the LTM8045 is through these pads,

so the printed circuit design has a large impact on the

thermal performance of the part. See the PCB Layout and

Thermal Considerations sections for more details. Return

the feedback divider (RFB) to this net.

VIN(Bank4):TheVINpinsuppliescurrenttotheLTM8045’s

internal regulator and to the internal power switch. This

pin must be locally bypassed with an external, low ESR

capacitor.

FB (Pin A3): If configured as a SEPIC, the LTM8045

regulates its FB pin to 1.215V. Apply a resistor between

FB and VOUT+. Its value should be RFB = [(VOUT – 1.215)/

0.0833]kΩ. If the LTM8045 is configured as an inverting

converter,theLTM8045regulatestheFBpinto5mV.Apply

a resistor between FB and VOUT– of value RFB = [(|VOUT|

+ 0.005)/0.0833]kΩ.

SYNC (Pin E1): To synchronize the switching frequency

to an outside clock, simply drive this pin with a clock. The

high voltage level of the clock needs to exceed 1.3V, and

the low level should be less than 0.4V. Drive this pin to

less than 0.4V to revert to the internal free running clock.

Ground this pin if the SYNC function is not used. See the

Applications Information section for more information.

SS(PinF1):Placeasoft-startcapacitorhere.Uponstart-up,

the SS pin will be charged by a (nominally) 275k resistor

to about 2.2V.

RT (Pin G1): The RT pin is used to program the switching

frequency of the LTM8045 by connecting a resistor from

this pin to ground. The necessary resistor value for the

LTM8045isdeterminedbytheequationRT=(91.9/fOSC)–1,

where fOSC is the typical switching frequency in MHz and

RT is in kΩ. Do not leave this pin open.

RUN (Pin G3): This pin is used to enable/disable the chip

and restart the soft-start sequence. Drive below 1.235V

to disable the chip. Drive above 1.385V to activate chip

and restart the soft-start sequence. Do not float this pin.

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