LT5401 datasheet(9/16 Pages) AD

9 / 16 page

LT5401

Rev. 0

For more information www.analog.com

Figure 1. A Simplified FDA Noise Model

Table 2. Typical LT5401 Resistor Values

GAIN (dB)

RF (Ω)

RI (Ω)

1050

1400

700

–6

700

1400

Table 3. FDA Noise, 2VP-P BW and ISUPPLY

FDA

eni

(nV/√Hz)

(pA/√Hz)

(MHz)

(mA)

LTC6404-1

1.5

ADA4945-1

1.8

LTC6403-1

2.8

1.8

ADA4938-1

2.8

800

LTC6363

2.9

0.55

1.75

ADA4932-1

3.6

360

8.8

LTC6362

3.9

0.8

ADA4940-1

3.9

0.8

1.25

eno = eni • 1+

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

+ 2 • In •RF

(

)

+ 2 • enRI •

⎛

⎝

⎜

⎞

⎠

⎟

⎛

⎝

⎜

⎞

⎠

⎟

+ 2 • enRF

(1)

Bandwidth

Figure 2 shows an FDA circuit model with the LT5401

resistors and parasitic capacitors CP and an external feed-

back capacitor CF. The gain setting resistors and CP form

distributed input and feedback poles. The input poles pro-

vide a useful attenuation at very high frequencies and the

feedback poles add gain peaking (without any feedback

capacitor). In addition, CP at the FDA inputs and the gain

setting resistors form a parasitic pole that increases gain

peaking and can cause instability. A feedback capacitor

CF is required to mitigate the excessive gain peaking of

multiple parasitic poles. A CF ≥ 3.3pF is recommended for

6dB gain (use higher CF values for 0dB and –6dB gains).

The CP capacitor at the FDA outputs is a CLOAD and can

lower the amplifier’s phase margin (consider the gain

peaking sensitivity of the Frequency Response vs CLOAD

plot in the FDA data sheet).

PCB Layout

A PCB layout for an FDA must be differentially symmetri-

cal and matched from input to output using short traces

and striping copper from under the trace to minimize

FDA

–

5401 F01

enRF2

enRI2

enRF2

enRI2

eno2

eni2

in–2

in+2

APPLICATIONS INFORMATION

Figure 2. Simplified LT5401 and FDA Model. CP is

a 3.4pF Parasitic Capacitance and CF is an External

Feedback Capacitor

FDA

–

5401 F02

350Ω

700Ω

350Ω

700Ω

OUT2

IN2

350Ω

700Ω

350Ω

700Ω

OUT1

IN1

GAIN CONNECTION

–6dB

6dB

0dB

–6dB

6dB

0dB

LT5401 Datasheet(PDF) 9 Page - Analog Devices

LT5401 Datasheet(HTML) 9 Page - Analog Devices

Html Pages

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

Datasheet Download

Link URL