MAX4292 Maxim, MAX4292 Datasheet - Page 12

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

When the output of the comparator is low, the supply
current increases. The output stage has biasing circuit-
ry to monitor the output current. When the amplifier is
used as a comparator, the output stage is overdriven
and the current through the biasing circuitry increases
to maximum. For the MAX4291, typical supply currents
increase to 1.5mA with V
V
The MAX4291/MAX4292/MAX4294 are ideal for appli-
cations powered from a two-cell battery stack. Figure
11 shows an application circuit in which the MAX4291
is used for monitoring the current of a two-cell 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
Ultra-Small, 1.8V, µPower,
Rail-to-Rail I/O Op Amps
Figure 8. Propagation Delay vs. Input Overdrive
12
CC
Using the MAX4291/MAX4292/MAX4294
= 5.0V (Figure 10).
______________________________________________________________________________________
1000
100
10
V
V
V
HYST
HI
LO
0
as Low-Power Current Monitors
10
t
PD
20 30
1
V
PROPAGATION DELAY
+
vs. INPUT OVERDRIVE
HI
t
,
PD
V
V
CC
-
HI
,
V
= 5.5V
R2
CC
R1
t
40 50
PD
V
OD
CC
= 5.5V
-
R
,
V
V
(mV)
HYST
CC
R1
LO
= 1.8V and to 9mA when
60
= 1.8V
R
t
PD
HYST
70
R1
+
,
V
V
CC
80
CC
= 1.8V
90
V
REF
100
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. To
minimize errors, scale R1 to give a voltage drop that is
large enough in comparison to the op amp’s V
Calculate the output voltage of the application using
the following equation:
Figure 9. Hysteresis Comparator Circuit
Figure 10. Maximum Supply Current per Amplifier vs. Supply
Voltage
INPUT
OUTPUT
V
SIG
V
V
V
LO
HI
OUT
12
10
MAXIMUM SUPPLY CURRENT PER AMPLIFIER
8
6
4
2
0
0
R1
R2
COMPARATOR CONFIGURATION
V
IN
0.5
+ = (V
1.0
I
LOAD
IN
V
vs. SUPPLY VOLTAGE
1.5
EE
-) - 100mV
SUPPLY VOLTAGE (V)
= GND
V
REF
2.0 2.5 3.0
R2
R1
R
V
V
HYST
CC
EE
3.5
= GND
4.0
4.5 5.0
MAX4291
MAX4292
MAX4294
R3
V
OUT
HYSTERESIS
V
V
OH
OL
5.5
OS
.