LMH6715QML-SP datasheet(11/18 Pages) TI1

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LMH6715QML

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SNOSAQ3B – NOVEMBER 2010 – REVISED MAY 2013

Figure 31. RF vs. Inverting Gain

When using the LMH6715 as a replacement for the CLC412, identical bandwidth can be obtained by using an

appropriate value of RF . The chart “Frequency Response vs. RF” shows that an RF of approximately 700Ω will

provide bandwidth very close to that of the CLC412. At other gains a similar increase in RF can be used to match

the new and old parts.

CIRCUIT LAYOUT

With all high frequency devices, board layouts with stray capacitances have a strong influence over AC

performance. The LMH6715 is no exception and its input and output pins are particularly sensitive to the coupling

of parasitic capacitances (to AC ground) arising from traces or pads placed too closely (<0.1”) to power or

ground planes. In some cases, due to the frequency response peaking caused by these parasitics, a small

adjustment of the feedback resistor value will serve to compensate the frequency response. Also, it is very

important to keep the parasitic capacitance across the feedback resistor to an absolute minimum.

The performance plots in the data sheet can be reproduced using the evaluation boards available from Texas

Instruments. The LMH730036 board uses all SMT parts for the evaluation of the LMH6715. The board can serve

as an example layout for the final production printed circuit board.

Care must also be taken with the LMH6715's layout in order to achieve the best circuit performance, particularly

channel-to-channel isolation. The decoupling capacitors (both tantalum and ceramic) must be chosen with good

high frequency characteristics to decouple the power supplies and the physical placement of the LMH6715's

external components is critical. Grouping each amplifier's external components with their own ground connection

and separating them from the external components of the opposing channel with the maximum possible distance

is recommended. The input (RIN) and gain setting resistors (RF) are the most critical. It is also recommended that

the ceramic decoupling capacitor (0.1

μF chip or radial-leaded with low ESR) should be placed as closely to the

power pins as possible.

POWER DISSIPATION

Follow these steps to determine the Maximum power dissipation for the LMH6715:

1. Calculate the quiescent (no-load) power: PAMP = ICC (VCC - VEE)

2. Calculate the RMS power at the output stage: PO = (VCC -VLOAD)(ILOAD), where VLOAD and ILOAD are the voltage

and current across the external load.

3. Calculate the total RMS power: Pt = PAMP + PO

The maximum power that the LMH6715, package can dissipate at a given temperature can be derived with the

following equation:

Pmax = (150º - Tamb)/

θJA

where

•

Tamb = Ambient temperature (°C)

•

θJA = Thermal resistance, from junction to ambient, for a given package (°C/W)

(1)

For the CDIP package

θJA is 140°C/W.

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