MAX4292 Maxim, MAX4292 Datasheet - Page 9

• Manufacturer Part Number: MAX4292
• Description: The MAX4291/MAX4292/MAX4294 family of micropower operational amplifiers operates from a 1
• Manufacturer: Maxim

capacitance) creates a parasitic pole that produces an
underdamped signal response. Reducing input capaci-
tance or placing a small capacitor across the feedback
resistor improves response in this case.
The MAX4291/MAX4292/MAX4294 family’s inputs are
protected from large differential input voltages by inter-
nal 10.6k
diode stacks across the inputs (Figure 2). For
differential input voltages (much less than 1.8V), input
resistance is typically 0.75M . For differential input
voltages greater than 1.8V, input resistance is around
21.2k , and the input bias current can be approximat-
ed by the following equation:
In the region where the differential input voltage
approaches 1.8V, the input resistance decreases expo-
nentially from 0.75M
begins to conduct. Conversely, the bias current
increases with the same curve.
In unity-gain configuration, high slew-rate input signals
may capacitively couple to the output through the triple-
diode stacks.
Table 1. MAX4291 Characteristics with Typical Battery Systems
Figure 2. Input Protection Circuit
BATTERY TYPE
Alkaline (2 cells)
Nickel-Cadmium
(2 cells)
Lithium-Ion
(1 cell)
Nickel-Metal-
Hydride (2 cells)
IN+
IN-
10.6k
10.6k
series resistors and back-to-back triple-
I
BIAS
_______________________________________________________________________________________
RECHARGE-
(V
ABLE
to 21.2k
Yes
Yes
Yes
No
DIFF
21.2k
- 1.8V)
as the diode block
V
FRESH
3.0
2.4
3.5
2.4
(V)
V
END-OF-LIFE
Ultra-Small, 1.8V, µPower,
1.8
1.8
2.7
1.8
Rail-to-Rail I/O Op Amps
The MAX4291/MAX4292/MAX4294 output stage can
drive up to a 2k
the rails. Figure 3 shows the output-voltage swing of a
MAX4291 configured as a unity-gain buffer, powered
from a ±2.5V supply. The output for this setup typically
swings from (V
load.
The MAX4291/MAX4292/MAX4294 operate from a sin-
gle 1.8V to 5.5V supply (or dual ±0.9V to ±2.75V sup-
plies) and consume only 100µA of supply current per
amplifier. A high power-supply rejection ratio of 100dB
allows the amplifiers to be powered directly off a
decaying battery voltage, simplifying design and
extending battery life.
The MAX4291/MAX4292/MAX4294 are ideally suited for
use with most battery-powered systems. Table 1 lists a
Figure 3. Rail-to-Rail Input/Output Voltage Range
(V)
2.5V/div
2.5V/div
OUT
CAPACITY, AA SIZE
IN
V
EE
CC
Applications Information
(mA-h)
= 2.5V, V
2000
1000
1000
Power-Supply Considerations
750
+ 25mV) to (V
load and still swing to within 46mV of
EE =
Rail-to-Rail Output Stage
-2.5V
20 s/div
CC
OPERATING TIME IN
- 2mV) with a 100k
NORMAL MODE
MAX4291
20,000
10,000
10,000
7500
(h)
0
0
9