LMH6629MFSLASHNOPB datasheet(22/45 Pages) TI

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zero"

Gain

Noise

)

4.0

2.0

0.0

-2.0

-4.0

-6.0

f (MHz)

Cf ¶

100

1,000

10,000

LMH6629

SNOSB18I – APRIL 2010 – REVISED DECEMBER 2014

www.ti.com

Feature Description (continued)

Cf = 1.5 pF

RA = 33 Ω

RB = 91 Ω

Figure 51. SOT-23-5 Package Low Closed Loop Gain Operation

with External Compensation

For the Figure 51 measured results, a compensation capacitor (Cf') was used across Rf to compensate for the

summing node net capacitance due to the board and the SOT-23–5 LMH6629. The RA and RB combination

reduces the effective capacitance of Cf‘ by the ratio of 1+RB / RA, with the constraint that RB << Rf, thereby

allowing a practical capacitance value (> 1pF) to be used. The WSON-8 package does not need this

compensation across Rf due to its lower parasitics.

With the COMP pin HI (WSON-8 package only) or with the SOT-23–5 package, this circuit achieves high slew

rate and takes advantage of the LMH6629’s superior low-noise characteristics without sacrificing stability, while

enabling lower gain applications. It should be noted that the Rc, Cc combination does lower the input impedance

and increases noise gain at higher frequencies. With these values, the input impedance reduces by 3 dB at 490

MHz. The Noise Gain transfer function “zero” is given by Equation 1 and it has a 3-dB increase at 32.8 MHz with

these values:

External Compensation Noise Gain Increase:

(1)

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LMH6629MF/NOPB Datasheet(PDF) 22 Page - Texas Instruments