LT6300IGN datasheet(11/16 Pages) LINER

11 / 16 page

LT6300

APPLICATIO S I FOR ATIO

Heat Sinking Using PCB Metal

Designing a thermal management system is often a trial

and error process as it is never certain how effective it is

until it is manufactured and evaluated. As a general rule,

the more copper area of a PCB used for spreading heat

away from the driver package, the more the operating

junction temperature of the driver will be reduced. The

limit to this approach however is the need for very com-

pact circuit layout to allow more ports to be implemented

on any given size PCB.

To best extract heat from the GN16 package, a generous

area of top layer PCB metal should be connected to the four

corner pins (Pins 1, 8, 9 and 16). These pins are fused to

the leadframe where the LT6300 die is attached. It is

important to note that this heat spreading metal area is

electrically connected to the V– supply voltage.

Fortunately xDSL circuit boards use multiple layers of

metal for interconnection of components. Areas of metal

beneath the LT6300 connected together through several

small 13 mil vias can be effective in conducting heat away

from the driver package. The use of inner layer metal can

free up top and bottom layer PCB area for external compo-

nent placement.

When PCB cards containing multiple ports are inserted

into a rack in an enclosed cabinet, it is often necessary to

provide airflow through the cabinet and over the cards.

This is also very effective in reducing the junction-to-

ambient thermal resistance of each line driver. To a limit,

this thermal resistance can be reduced approximately

°C/W for every 100lfpm of laminar airflow.

Layout and Passive Components

With a gain bandwidth product of 200MHz the LT6300

requires attention to detail in order to extract maximum

performance. Use a ground plane, short lead lengths and

a combination of RF-quality supply bypass capacitors (i.e.,

0.1

µF). As the primary applications have high drive cur-

rent, use low ESR supply bypass capacitors (1

µF to 10µF).

The parallel combination of the feedback resistor and gain

setting resistor on the inverting input can combine with

the input capacitance to form a pole that can cause

frequency peaking. In general, use feedback resistors of

1k or less.

Compensation

The LT6300 is stable in a gain 10 or higher for any supply

and resistive load. It is easily compensated for lower gains

with a single resistor or a resistor plus a capacitor.

Figure 8 shows that for inverting gains, a resistor from the

inverting node to AC ground guarantees stability if the

parallel combination of RC and RG is less than or equal to

RF/9. For lowest distortion and DC output offset, a series

capacitor, CC, can be used to reduce the noise gain at

lower frequencies. The break frequency produced by RC

and CC should be less than 5MHz to minimize peaking.

Figure 9 shows compensation in the noninverting configu-

ration. The RC, CC network acts similarly to the inverting

case. The input impedance is not reduced because the

network is bootstrapped. This network can also be placed

between the inverting input and an AC ground.

Figure 8. Compensation for Inverting Gains

(OPTIONAL)

6300 F08

–RF

< 5MHz

πRCCC

(RC || RG) ≤ RF/9

(OPTIONAL)

6300 F09

= 1 +

< 5MHz

πRCCC

(RC || RG) ≤ RF/9

Figure 9. Compensation for Noninverting Gains

LT6300IGN Folha de dados(PDF) 11 Page - Linear Technology

LT6300IGN Folha de dados(HTML) 11 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Folha de dados Download

Ligação URL