Datasheet LT5401 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Matched Resistor Network for Precision Amplifiers |
| Pages / Page | 16 / 9 — APPLICATIONS INFORMATION Table 2. Typical LT5401 Resistor Values. GAIN … |
| File Format / Size | PDF / 955 Kb |
| Document Language | English |
APPLICATIONS INFORMATION Table 2. Typical LT5401 Resistor Values. GAIN (dB). RF (Ω). RI (Ω). Table 3. FDA Noise, 2V
Model Line for this Datasheet
Text Version of Document
link to page 9 LT5401
APPLICATIONS INFORMATION Table 2. Typical LT5401 Resistor Values
distributed input and feedback poles. The input poles pro-
GAIN (dB) RF (Ω) RI (Ω)
vide a useful attenuation at very high frequencies and the 0 1050 1050 feedback poles add gain peaking (without any feedback 6 1400 700 capacitor). In addition, CP at the FDA inputs and the gain –6 700 1400 setting resistors form a parasitic pole that increases gain peaking and can cause instability. A feedback capacitor
Table 3. FDA Noise, 2V
C
P-P BW and ISUPPLY
F is required to mitigate the excessive gain peaking of
e
multiple parasitic poles. A C
ni In BW Is
F ≥ 3.3pF is recommended for
FDA (nV/√Hz) (pA/√Hz) (MHz) (mA)
6dB gain (use higher CF values for 0dB and –6dB gains). LTC6404-1 1.5 3 72 27 The CP capacitor at the FDA outputs is a CLOAD and can ADA4945-1 1.8 1 60 4 lower the amplifier’s phase margin (consider the gain LTC6403-1 2.8 1.8 32 11 peaking sensitivity of the Frequency Response vs CLOAD ADA4938-1 2.8 5 800 34 plot in the FDA data sheet). LTC6363 2.9 0.55 35 1.75 ADA4932-1 3.6 1 360 8.8
PCB Layout
LTC6362 3.9 0.8 7 1 A PCB layout for an FDA must be differentially symmetri- ADA4940-1 3.9 0.8 25 1.25 cal and matched from input to output using short traces and striping copper from under the trace to minimize ⎛ 2 2 ⎛ R ⎞⎞ ⎛ ⎛R ⎞⎞ e F F 2 CP CP CP CP no = ⎜eni • ⎜1+ ⎟⎟ + 2 • I ( n •RF )2 +2 •⎜enRI •⎜ ⎟⎟ +2 • enRF (1) ⎝ ⎝ R ⎝ ⎝ R I ⎠⎠ I ⎠⎠ 700Ω 350Ω 350Ω 700Ω IN1 1 5 4 3 2 OUT1
Bandwidth
0dB 6dB –6dB Figure 2 shows an FDA circuit model with the LT5401 CF resistors and parasitic capacitors CP and an external feed- back capacitor CF. The gain setting resistors and CP form + R enRF2 enRI2 I RF GAIN CONNECTION FDA in+2 – C + F FDA e 6dB –6dB no2 in–2 – 0dB 700Ω 350Ω 350Ω 700Ω IN2 10 6 7 8 9 OUT2 e R ni2 enRF2 enRI2 CP CP CP C I RF P 5401 F02 5401 F01
Figure 1. A Simplified FDA Noise Model Figure 2. Simplified LT5401 and FDA Model. CP is a 3.4pF Parasitic Capacitance and CF is an External Feedback Capacitor
Rev. 0 For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Typical Application Related Parts
APPLICATIONS INFORMATION Table 2. Typical LT5401 Resistor Values
distributed input and feedback poles. The input poles pro-
GAIN (dB) RF (Ω) RI (Ω)
vide a useful attenuation at very high frequencies and the 0 1050 1050 feedback poles add gain peaking (without any feedback 6 1400 700 capacitor). In addition, CP at the FDA inputs and the gain –6 700 1400 setting resistors form a parasitic pole that increases gain peaking and can cause instability. A feedback capacitor
Table 3. FDA Noise, 2V
C
P-P BW and ISUPPLY
F is required to mitigate the excessive gain peaking of
e
multiple parasitic poles. A C
ni In BW Is
F ≥ 3.3pF is recommended for
FDA (nV/√Hz) (pA/√Hz) (MHz) (mA)
6dB gain (use higher CF values for 0dB and –6dB gains). LTC6404-1 1.5 3 72 27 The CP capacitor at the FDA outputs is a CLOAD and can ADA4945-1 1.8 1 60 4 lower the amplifier’s phase margin (consider the gain LTC6403-1 2.8 1.8 32 11 peaking sensitivity of the Frequency Response vs CLOAD ADA4938-1 2.8 5 800 34 plot in the FDA data sheet). LTC6363 2.9 0.55 35 1.75 ADA4932-1 3.6 1 360 8.8
PCB Layout
LTC6362 3.9 0.8 7 1 A PCB layout for an FDA must be differentially symmetri- ADA4940-1 3.9 0.8 25 1.25 cal and matched from input to output using short traces and striping copper from under the trace to minimize ⎛ 2 2 ⎛ R ⎞⎞ ⎛ ⎛R ⎞⎞ e F F 2 CP CP CP CP no = ⎜eni • ⎜1+ ⎟⎟ + 2 • I ( n •RF )2 +2 •⎜enRI •⎜ ⎟⎟ +2 • enRF (1) ⎝ ⎝ R ⎝ ⎝ R I ⎠⎠ I ⎠⎠ 700Ω 350Ω 350Ω 700Ω IN1 1 5 4 3 2 OUT1
Bandwidth
0dB 6dB –6dB Figure 2 shows an FDA circuit model with the LT5401 CF resistors and parasitic capacitors CP and an external feed- back capacitor CF. The gain setting resistors and CP form + R enRF2 enRI2 I RF GAIN CONNECTION FDA in+2 – C + F FDA e 6dB –6dB no2 in–2 – 0dB 700Ω 350Ω 350Ω 700Ω IN2 10 6 7 8 9 OUT2 e R ni2 enRF2 enRI2 CP CP CP C I RF P 5401 F02 5401 F01
Figure 1. A Simplified FDA Noise Model Figure 2. Simplified LT5401 and FDA Model. CP is a 3.4pF Parasitic Capacitance and CF is an External Feedback Capacitor
Rev. 0 For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Typical Application Related Parts
