LMX358ASA Maxim Integrated Products, LMX358ASA Datasheet - Page 9

• Manufacturer Part Number: LMX358ASA
• Description: Single/Dual/Quad/ General-Purpose/ Low-Voltage/ Rail-to-Rail Output Op Amps
• Manufacturer: Maxim Integrated Products

Figure 1. Input Protection Circuit
Figure 2. Rail-to-Rail Output Swing
The LMX321/LMX358/LMX324’s inputs are protected
from large differential input voltages by internal 3.5k
series resistors and back-to-back triple diode stacks
across the inputs (Figure 1). For differential input volt-
ages (much less than 1.8V), input resistance is typically
3M . For differential input voltages greater than 1.8V,
input resistance is around 7k , and the input bias cur-
rent can be approximated by the following equation:
In the region where the differential input voltage
approaches 1.8V, input resistance decreases exponen-
tially from 3M
ducting. Inversely, the bias current increases with the
same curve.
The LMX321/LMX358/LMX324 drive 2k
typically swing within 40mV of the supply rails. Figure 2
1V/div
2V/div
V
OUT
V
3.5k
3.5k
IN
I
V
Low-Voltage, Rail-to-Rail Output Op Amps
BIAS
CC
to 7k
= 2.5V, V
_______________________________________________________________________________________
= (V
EE
Detailed Description
Rail-to-Rail Output Stage
as the diode block begins con-
DIFF
= -2.5V, A
Input Protection Circuit
200 s/div
- 1.8V) / 7k
VCL
Single/Dual/Quad, General-Purpose,
= 2V/V
loads and still
2.5V
-2.5V
shows the output voltage swing of the LMX321 config-
ured with A
Driving a capacitive load can cause instability in many
op amps, especially those with low quiescent current.
The LMX321/LMX358/LMX324 are unity-gain stable for
a range of capacitive loads to above 400pF. Figure 4
shows the response of the LMX321 with an excessive
capacitive load. Adding a series resistor between the
output and the load capacitor (Figure 5) improves the
circuit’s response by isolating the load capacitance
from the op amp’s output.
The LMX321/LMX358/LMX324 outputs typically settle
within 10µs after power-up. Figure 6 shows the output
voltage on power-up and power-down.
Figure 3. Capacitive-Load-Driving Circuit
Figure 4. Output With Excessive Capacitive Load
100mV/div
100mV/div
V
OUT
VCL
V
IN
= +2V/V.
Applications Information
LMX321
LMX358
LMX324
Driving Capacitive Loads
V
CC
4 s/div
= 5V, V
EE
= 0, C
R
L
R
L
L
= 2.2nF
= 2k
Power-Up
2.6V
2.4V
2.6V
2.4V
C
L
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