LTC6252 Linear Technology, LTC6252 Datasheet - Page 17

• Manufacturer Part Number: LTC6252
• Description: 3.5mA Power Efficient Rail-to-Rail I/O Op Amps
• Manufacturer: Linear Technology

DataSheet.in
TYPICAL APPLICATIONS
Low Noise Gain Block Using Channels in Parallel
Figure 5 shows the LTC6254 confi gured as a low noise
gain block. By confi guring each channel as a gain of 10
block and putting all four gain blocks in parallel, the input
referred noise can be reduced signifi cantly. 22Ω resistors
are hooked up to the outputs of each of the channels to
ensure even distribution of load currents.For a total sup-
ply current of 13.2mA, measured input referred noise
density (including contributions from the resistors) be-
tween 100kHz and 10MHz was less than 1.6nV/√Hz, with
input referred noise density at 1 MHz being 1.5nV/√Hz.
The measured –3dB frequency was 37MHz for a load
resistance of 1k.
Figure 5. Low Noise Gain Block Using Parallel Channels
V
IN
100Ω
100Ω
100Ω
100Ω
–
+
–
+
–
+
–
+
¼ LTC6254
¼ LTC6254
¼ LTC6254
¼ LTC6254
1pF
1pF
1pF
1pF
–2.5V
2.5V
900Ω
900Ω
900Ω
900Ω
22Ω
22Ω
22Ω
22Ω
625234 F05
V
OUT
Multiplexing Channels
The LTC6252 and LTC6253 are available with shutdown
pins in the SOT-23 and MS10 packages. While this allows
for reduced power consumption, it also makes the parts
suitable for high output impedance applications such as
muxing. During shutdown, the bases of the amplifi er’s
output channels are hard tied to their emitters in order to
minimize leakage. Figure 6 shows the LTC6253 applied as a
mux, with the outputs simply shorted together. Depending
on which device is powered, either the V
is buffered to V
logic inversion, so that pulling the gate high selects the
B path while the FET drain goes low shutting down the A
path. R3 is provided to speed up the drain rise time. The
LTC6253 turn-on time is longer than the turn-off time (3.5μs
vs < 2μs) avoiding cross conduction in the output stages.
LTC6252/LTC6253/LTC6254
SEL_B
5V
V
V
Figure 6. Multiplexing Channels
A
B
OUT
330Ω
330Ω
20k
R1
R2
R3
. The MOSFET Q1 provides a simple
Q1
2N7002
½ LTC6253
½ LTC6253
625234 F06
5V
SHDNA
SHDNB
A
or the V
V
OUT
17
B
input
625234f