Datasheet

MAX9922/MAX9923
Ultra-Precision, High-Side
Current-Sense Amplifiers
10 ______________________________________________________________________________________
Detailed Description
The MAX9922/MAX9923 high-side, current-sense
amplifiers implement a spread-spectrum autozeroing
technique that minimizes the input offset error, offset
drift over time and temperature, and the effect of 1/f
noise. This technique achieves less than 25µV (max)
offset voltage.
The MAX9922/MAX9923 high-side current-sense ampli-
fiers feature a +1.9V to +28V input common-mode
range that is independent of supply voltage (V
DD
). This
feature allows the monitoring of current out of a battery
as low as +1.9V and enables high-side current sensing
at voltages greater than the supply voltage.
The MAX9922/MAX9923 monitor current through a cur-
rent-sense resistor and amplify the voltage across the
resistor. The 28V input common-mode voltage (V
RS+
)
range of the MAX9922/MAX9923 is independent of the
supply voltage (V
DD
). High-side current monitoring
does not interfere with the ground path of the load
being measured, making the MAX9922/MAX9923 par-
ticularly useful in a wide range of high-voltage systems.
The MAX9922/MAX9923 use Maxim’s indirect current
feedback achitecture. This architecture con-
verts the differential input voltage signal to a current
through an input transconductance stage. An output
transconductance stage converts a portion of the output
voltage (equal to the output voltage divided by the
gain) into another precision current. These two currents
are subtracted and the result is fed to a loop amplifier
with sufficient gain to minimize errors (see the
Functional Diagrams.)
Battery-powered systems require a precise bidirection-
al current-sense amplifier to accurately monitor the bat-
tery’s charge and discharge currents. Measurements of
OUT with respect to V
REF
yield a positive and negative
voltage during charge and discharge cycles (Figure 1).
The MAX9922 allows adjustable gain with a pair of exter-
nal resistors between OUT, FB, and REF. The MAX9923T/
MAX9923H/MAX9923F use laser-trimmed internal resis-
tors for fixed gains of 25, 100, and 250, respectively, with
0.5% gain accuracy (see the Functional Diagrams. )
Functional Diagrams
MAX9922
RSB
1
RS-
RS+
2
3
N.C.
4
GND
5
V
DD
10
R2
R1
OUT
FB
REF
9
8
7
SHDN
6
GAIN = 1 +
(
R2
)
R1
MAX9923
RSB
1
RS-
RS+
2
3
N.C.
4
GND
5
V
DD
10
R2
R1
SHDN
6
OUT
9
FB
8
REF
7
MAX9923
VERSION
GAIN
T25
H 100
F 250