LTM8046 datasheet(8/20 Pages) LINER

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LTM8046

8046fb

For more information www.linear.com/LTM8046

pin FuncTions

VIN (Bank 1): VIN supplies current to the LTM8046’s

internal regulator and to the integrated power switch.

These pins must be locally bypassed with an external,

low ESR capacitor.

GND (Bank 2): This is the primary side local ground of

the LTM8046 primary. In most applications, the bulk of

the heat flow out of the LTM8046 is through the GND and

VOUT–pads,sotheprintedcircuitdesignhasalargeimpact

onthethermalperformanceofthepart.SeethePCBLayout

and Thermal Considerations sections for more details.

VOUT– (Bank 3): VOUT– is the return for VOUT. VOUT and

VOUT– comprise the isolated output of the LTM8046. In

most applications, the bulk of the heat flow out of the

LTM8046 is through the GND and VOUT– pads, so the

printed circuit design has a large impact on the thermal

performance of the part. See the PCB Layout and Thermal

Considerationssectionsformoredetails.Applyanexternal

capacitor between VOUT and VOUT–.

VOUT (Bank 4): VOUT and VOUT– comprise the isolated

output of the LTM8046 flyback stage. Apply an external

capacitor between VOUT and VOUT–. Do not allow VOUT– to

exceed VOUT.

RUN (Pin L3): A resistive divider connected to VIN and this

pin programs the minimum voltage at which the LTM8046

will operate. Below 1.24V, the LTM8046 does not deliver

power to the secondary. Above 1.24V, power will be de-

livered to the secondary and 8µA will be fed into the SS

pin. When RUN is less than 1.24V, the pin draws 2.5µA,

allowing for a programmable hysteresis. Do not allow a

negative voltage (relative to GND) on this pin.

BIAS (Pin L4): This pin supplies the power necessary to

operate the LTM8046. It must be locally bypassed with

a low ESR capacitor of at least 1μF. Do not allow this pin

voltage to rise above VIN.

SS(PinL5):Placeasoft-startcapacitorheretolimitinrush

current and the output voltage ramp rate. Do not allow a

negative voltage (relative to GND) on this pin.

FB (Pin L6): Apply a resistor from this pin to GND to set

the output voltage, using the recommended value given

in Table 1. If Table 1 does not list the desired VOUT value,

the equation

RFB = 31.6 VOUT–0.84

(

)kΩ

may be used to approximate the value. To the seasoned

designer, this exponential equation may seem unusual.

The equation is exponential due to non-linear current

sources that are used to temperature compensate the

output regulation.

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