LT6350HMS8#TRPBF Linear Technology, LT6350HMS8#TRPBF Datasheet - Page 25

• Manufacturer Part Number: LT6350HMS8#TRPBF
• Description: IC DIFF CONVERT/ADC DRIVER 8MSOP
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LT6350HMS8#TRPBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
100kHz, 3RD-ORDER BUTTERWORTH FILTER
The LT6350 can be confi gured as a single-ended to
differential fi lter incorporating feedback from the inverting
output. Figure 13 shows the schematic of the confi guration
with values giving a 3rd Order Butterworth characteristic
having a 100kHz –3dB point with a differential gain of four.
Figure 14 shows the fi lter output response to 10MHz. As
an option, to match the source impedance and preserve
the low DC errors of the LT6350, connect a 2.10k series
resistor at +IN1. To reduce the resistor noise, the +IN1
pin can be bypassed with a 0.1μF capacitor. For similar
topologies please consult the LT1567 data sheet and
design guide.
+
–
174Ω
V
IN
Figure 13. 100KHz, 3rd Order Butterworth Filter
2210Ω
0.01μF
1000pF
523Ω
R3
2.5V
+ IN1
8
– IN1
1
+
–
SHDN
4750Ω
2.5V
LT6350
7
+ IN2
2
499Ω
1000pF
C5
5V
V
–
+
3
+
0.1μF
V
–
6
6350 F13
0.1μF
OUT2
OUT1
5
4
V
V
OUT2
OUT1
Low Noise, Low Power 1MΩ Single Supply Photo-
diode Differential Output Transimpedance Amplifi er
The Typical Application on the back page shows the LT6350
applied as a differential output transimpedance amplifi er.
The LT6350 forces the BF862 ultralow noise JFET source
to 3V, with R2 ensuring that the JFET has an I
The JFET acts as a source follower, buffering the input of
the LT6350 and making it suitable for the high impedance
feedback element R1. The BF862 has a minimum I
10mA and a pinchoff voltage between –0.3V and –1.2V.
The JFET gate and OUT1 therefore sit at a point slightly
higher than one pinchoff voltage below 3V, about mid-
supply at 2.5V.
When the photodiode is illuminated, the current must come
from OUT1 through R1 as in a normal transimpedance
amplifi er. Amplifi er output noise density is dominated at
low frequency by the 130nV/√Hz of the feedback resistor,
rising to 210nV/√Hz at 1MHz. Note that because the JFET
has a high g
into R2 is only about 1%. The closed-loop bandwidth
using a 3pF photodiode was measured at approximately
1.35MHz. With the output taken differentially, the gain and
the noise are both doubled.
Figure 14. 100KHz, 3rd Order Butterworth Filter Response
–100
m
–20
–40
–60
–80
20
, approximately 1/30Ω, its attenuation looking
0
1K
10K
FREQUENCY (Hz)
100K
1M
6350 F14
LT6350
DRAIN
10M
of 1mA.
25
DSS
6350fb
of