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MAX4040ESA+T

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
MAX4040–MAX4044
Single/Dual/Quad, Low-Cost, SOT23,
Micropower, Rail-to-Rail I/O Op Amps
10 ______________________________________________________________________________________
Shutdown Mode
The MAX4041 (single) and MAX4043 (dual) feature a
low-power shutdown mode. When the shutdown pin
(SHDN) is pulled low, the supply current drops to 1µA
per amplifier, the amplifier is disabled, and the outputs
enter a high-impedance state. Pulling SHDN high or
leaving it floating enables the amplifier. Take care to
ensure that parasitic leakage current at the SHDN pin
does not inadvertently place the part into shutdown
mode when SHDN is left floating. Figure 4 shows the
output voltage response to a shutdown pulse. The logic
threshold for SHDN is always referred to V
CC
/ 2 (not to
GND). When using dual supplies, pull SHDN to V
EE
to
enter shutdown mode.
Load-Driving Capability
The MAX4040–MAX4044 are fully guaranteed over tem-
perature and supply voltage to drive a maximum resis-
tive load of 25kΩ to V
CC
/ 2, although heavier loads can
be driven in many applications. The rail-to-rail output
stage of the amplifier can be modeled as a current
source when driving the load toward V
CC
, and as a cur-
rent sink when driving the load toward V
EE
. The magni-
tude of this current source/sink varies with supply
voltage, ambient temperature, and lot-to-lot variations
of the units.
Figures 5a and 5b show the typical current source and
sink capability of the MAX4040–MAX4044 family as a
function of supply voltage and ambient temperature.
The contours on the graph depict the output current
value, based on driving the output voltage to within
50mV, 100mV, and 200mV of either power-supply rail.
1200
0
-60 -40 -20 100
200
400
1000
MAX4040-44 fig05a
TEMPERATURE (°C)
OUTPUT SOURCE CURRENT (µA)
04020
600
800
8060
V
CC
= 5.5V, V
OH
= 200mV
V
CC
= 5.5V, V
OH
= 100mV
V
CC
= 2.4V, V
OH
= 50mV
V
CC
= 5.5V, V
OH
= 50mV
V
CC
= 2.4V,
V
OH
= 200mV
V
CC
= 2.4V,
V
OH
= 100mV
Figure 5a. Output Source Current vs. Temperature
3000
0
-60 -40 -20 100
500
1000
2500
MAX4040-44 fig05b
TEMPERATURE (°C)
OUTPUT SINK CURRENT (µA)
04020
1500
2000
8060
V
CC
= 5.5V, V
OL
= 200mV
V
CC
= 2.4V, V
OL
= 200mV
V
CC
= 5.5V,
V
OL
= 100mV
V
CC
= 2.4V, V
OL
= 50mV
V
CC
= 5.5V, V
OL
= 50mV
V
CC
= 2.4V, V
OL
= 100mV
Figure 5b. Output Sink Current vs. Temperature
1V/div
OUT
IN
1V/div
MAX4040-44 fig03
200µs/div
R
L
= 100kΩ TIED TO V
EE
V
IN
= 4.0V
f
IN
= 1kHz
Figure 3. Rail-to-Rail Input/Output Voltage Range
MAX4040-44 fig04
200µs/div
5V/div
1V/div
SHDN
OUT
V
IN
= 2V
R
L
= 100kΩ TIED TO V
EE
Figure 4. Shutdown Enable/Disable Output Voltage
MAX4040–MAX4044
Single/Dual/Quad, Low-Cost, SOT23,
Micropower, Rail-to-Rail I/O Op Amps
______________________________________________________________________________________ 11
For example, a MAX4040 running from a single +2.4V
supply, operating at T
A
= +25°C, can source 240µA to
within 100mV of V
CC
and is capable of driving a 9.6kΩ
load resistor to V
EE
:
The same application can drive a 4.6kΩ load resistor
when terminated in V
CC
/ 2 (+1.2V in this case).
Driving Capacitive Loads
The MAX4040–MAX4044 are unity-gain stable for loads
up to 200pF (see Load Resistor vs. Capacitive Load
graph in Typical Operating Characteristics).
Applications that require greater capacitive drive capa-
bility should use an isolation resistor between the output
and the capacitive load (Figures 6a–6c). Note that this
alternative results in a loss of gain accuracy because
R
ISO
forms a voltage divider with the load resistor.
Power-Supply Bypassing and Layout
The MAX4040–MAX4044 family operates from either a
single +2.4V to +5.5V supply or dual ±1.2V to ±2.75V
supplies. For single-supply operation, bypass the
power supply with a 100nF capacitor to V
EE
(in this
case GND). For dual-supply operation, both the V
CC
and V
EE
supplies should be bypassed to ground with
separate 100nF capacitors.
Good PC board layout techniques optimize perfor-
mance by decreasing the amount of stray capacitance
at the op amp’s inputs and output. To decrease stray
capacitance, minimize trace lengths by placing exter-
nal components as close as possible to the op amp.
Surface-mount components are an excellent choice.
Using the MAX4040–MAX4044
as Comparators
Although optimized for use as operational amplifiers,
the MAX4040–MAX4044 can also be used as rail-to-rail
I/O comparators. Typical propagation delay depends
on the input overdrive voltage, as shown in Figure 7.
External hysteresis can be used to minimize the risk of
output oscillation. The positive feedback circuit, shown
in Figure 8, causes the input threshold to change when
the output voltage changes state. The two thresholds
create a hysteresis band that can be calculated by the
following equations:
V
HYST
= V
HI
- V
LO
V
LO
= V
IN
x R2 / (R1 + (R1 x R2 / R
HYST
) + R2)
V
HI
= [(R2 / R1 x V
IN
) + (R2 / R
HYST
) x V
CC
] /
(1 + R1 / R2 + R2 / R
HYST
)
R =
2.4V - 0.1V
240 A
9.6k to V
LEE
µ
=Ω
50mV/div
IN
OUT
50mV/div
MAX4040/42/44 fig06b
100µs/div
R
ISO
= NONE, R
L
= 100kΩ, C
L
= 700pF
Figure 6b. Pulse Response without Isolating Resistor
50mV/div
IN
OUT
50mV/div
MAX4040/42/44 fig06c
100µs/div
R
ISO
= 1kΩ, R
L
= 100kΩ, C
L
= 700pF
Figure 6c. Pulse Response with Isolating Resistor
R
ISO
C
L
R
L
MAX4040–
MAX4044
A
V
=
R
L
≈ 1
R
L
+ R
ISO
Figure 6a. Using a Resistor to Isolate a Capacitive Load from
the Op Amp
MAX4040–MAX4044
Single/Dual/Quad, Low-Cost, SOT23,
Micropower, Rail-to-Rail I/O Op Amps
12 ______________________________________________________________________________________
The MAX4040–MAX4044 contain special circuitry to
boost internal drive currents to the amplifier output
stage. This maximizes the output voltage range over
which the amplifiers are linear. In an open-loop com-
parator application, the excursion of the output voltage
is so close to the supply rails that the output stage tran-
sistors will saturate, causing the quiescent current to
increase from the normal 10µA. Typical quiescent cur-
rents increase to 35µA for the output saturating at V
CC
and 28µA for the output at V
EE
.
Using the MAX4040–MAX4044
as Ultra-Low-Power Current Monitors
The MAX4040–MAX4044 are ideal for applications pow-
ered from a battery stack. Figure 9 shows an application
circuit in which the MAX4040 is used for monitoring the
current of a battery stack. In this circuit, a current load is
applied, and the voltage drop at the battery terminal is
sensed.
The voltage on the load side of the battery stack is
equal to the voltage at the emitter of Q1, due to the
feedback loop containing the op amp. As the load cur-
rent increases, the voltage drop across R1 and R2
increases. Thus, R2 provides a fraction of the load cur-
rent (set by the ratio of R1 and R2) that flows into the
emitter of the PNP transistor. Neglecting PNP base cur-
rent, this current flows into R3, producing a ground-ref-
erenced voltage proportional to the load current. Scale
R1 to give a voltage drop large enough in comparison
to V
OS
of the op amp, in order to minimize errors.
The output voltage of the application can be calculated
using the following equation:
V
OUT
= [I
LOAD
x (R1 / R2)] x R3
For a 1V output and a current load of 50mA, the choice
of resistors can be R1 = 2Ω, R2 = 100kΩ, R3 = 1MΩ.
The circuit consumes less power (but is more suscepti-
ble to noise) with higher values of R1, R2, and R3.
R2
R1
V
IN
OUTPUT
INPUT
V
OH
V
OL
V
EE
V
CC
V
OUT
R
HYST
V
EE
MAX4040–
MAX4044
HYSTERESIS
V
LO
V
OH
V
HI
Figure 8. Hysteresis Comparator Circuit
R1
I
LOAD
R2
V
CC
V
EE
R3
V
OUT
Q1
MAX4040
Figure 9. Current Monitor for a Battery Stack
10,000
10
0203010 100
100
1000
MAX4040-44 fig07
V
OD
(mV)
t
PD
(µs)
40 50 60 70 80
90
t
PD
-; V
CC
= +5V
t
PD
+; V
CC
= +2.4V
t
PD
-; V
CC
= +2.4V
t
PD
+; V
CC
= +5V
Figure 7. Propagation Delay vs. Input Overdrive
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

MAX4040ESA+T

Mfr. #:
Buy MAX4040ESA+T
Manufacturer:
Maxim Integrated
Description:
Operational Amplifiers - Op Amps uPower Rail-Rail
Lifecycle:
New from this manufacturer.
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