LMX358 Maxim, LMX358 Datasheet - Page 9

• Manufacturer Part Number: LMX358
• Description: The LMX321/LMX358/LMX324 are single/dual/quad, low-cost, low-voltage, pin-to-pin compatible upgrades to the LMV321/LMV358/LMV324 family of general purpose op amps
• Manufacturer: Maxim

The LMX321/LMX358/LMX324’s inputs are protected
from large differential input voltages by internal 3.5kΩ
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
3MΩ. For differential input voltages greater than 1.8V,
input resistance is around 7kΩ, 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 3MΩ to 7kΩ as the diode block begins con-
ducting. Inversely, the bias current increases with the
same curve.
Figure 1. Input Protection Circuit
Figure 2. Rail-to-Rail Output Swing
2V/div
1V/div
V
OUT
V
IN
3.5kΩ
3.5kΩ
V
I
CC
Low-Voltage, Rail-to-Rail Output Op Amps
BIAS
= 2.5V, V
_______________________________________________________________________________________
= (V
EE
Detailed Description
= -2.5V, A
DIFF
Input Protection Circuit
200µs/div
- 1.8V) / 7kΩ
VCL
Single/Dual/Quad, General-Purpose,
= 2V/V
2.5V
-2.5V
The LMX321/LMX358/LMX324 drive 2kΩ loads and still
typically swing within 40mV of the supply rails. Figure 2
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.
Figure 3. Capacitive-Load-Driving Circuit
Figure 4. Output With Excessive Capacitive Load
100mV/div
100mV/div
V
VCL
OUT
V
IN
= +2V/V.
V
CC
= 5V, V
LMX321
LMX358
LMX324
Driving Capacitive Loads
Rail-to-Rail Output Stage
EE
= 0V, C
4µs/div
L
= 2.2nF, R
R
L
L
= 2kΩ
2.6V
2.4V
2.6V
2.4V
C
L
9