LM6182IM datasheet(19/24 Pages) NSC

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Typical Applications (Continued)

POWER SUPPLY BYPASSING AND LAYOUT

CONSIDERATIONS

A fundamental requirement for high-speed amplifier design

is adequate bypassing of the power supply. It is critical to

maintain a wideband low-impedance to ground at the ampli-

fiers supply pins to insure the fidelity of high speed amplifier

transient signals. 0.1 µF ceramic bypass capacitors at each

supply pin are sufficient for many applications. Typically

10 µF tantalum capacitors are also required if large current

transients are delivered to the load. The bypass capacitors

should be placed as close to the amplifier pins as possible,

such as 0.5" or less.

Applications requiring high output power, cable drivers for

example, cause increased internal power dissipation. Inter-

nal power dissipation can be minimized by operating at re-

duced power supply voltages, such as ±5V.

Optimum heat dissipation is achieved by using wide circuit

board traces and soldering the part directly onto the board.

Large power supply and ground planes will improve power

dissipation. Safe Operating Area (S.O.A.) is determined us-

ing the Maximum Power Derating Curves.

The 16-pin small outline package (M) has 5 V− heat sinking

pins that enable a junction-to-ambient thermal resistance of

70˚C/W when soldered to 2 in

2 1 oz. copper trace. A V− heat

sinking pin is located on each corner of the package for ease

of layout. This allows high output power and/or operation at

elevated ambient temperatures without the additional cost of

an integrated circuit heat sink. If the heat sinking capabilities

of the S.O. package are not needed, pin 4 and at least one

of pins 1,8,9, or 16 must be connected to V− for proper op-

eration.

Figure 11 shows recommended copper patterns used to dis-

sipate heat from the LM6182.

CROSSTALK REJECTION

The LM6182 has an excellant crosstalk rejection value of

62 dB at 10 MHz. This value is made possible because the

LM6182 amplifiers share no common circuitry other than the

supply. High frequency crosstalk that does appear is prima-

rily caused by the magnetic and capacitive coupling of the in-

ternal bond wires. Bond wires connect the die to the package

lead frame. The amount of current flowing through the bond

wires is proportional to the amount of crosstalk. Therefore,

crosstalk rejection ratings will degrade when driving heavy

loads.

Figure 12 and shows a 10 dB difference for two differ-

ent loads.

DS011926-34

10A

DS011926-35

10B

FIGURE 10. Resistive Isolation of C

L Provides Higher

Fidelity Pulse Response. R

f and Rs Could Also Be

Increased to Maintain A

V = −1 and Improve Pulse

Response Characteristics.

DS011926-36

8-pin DIP (N)

DS011926-37

16-pin S.O. (M)

FIGURE 11. Copper Heatsink Layouts

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