MAX9938 Maxim, MAX9938 Datasheet - Page 8

• Manufacturer Part Number: MAX9938
• Description: The MAX9938 high-side current-sense amplifier offers precision accuracy specifications of VOS less than 500µV (max) and gain error less than 0
• Manufacturer: Maxim

1µA, 4-Bump UCSP/SOT23,
Precision Current-Sense Amplifier
The MAX9938 allows two methods of filtering to help
improve performance in the presence of input common-
mode voltage and input differential voltage transients.
Figure 1 shows a differential input filter.
The capacitor CIN between RS+ and RS- along with the
resistor RIN between the sense resistor and RS- helps
filter against input differential voltages and prevents
them from reaching the MAX9938.
The corner frequency of this filter is determined by the
choice of RIN, CIN, and the value of the input resis-
tance at RS- (R
ferent gain options.
The value of RIN should be chosen to minimize its
effect on the input offset voltage due to the bias current
at RS-. RIN x I
set. I
Figure 1. Differential Input Filter
8
_______________________________________________________________________________________
BIAS
is typically 0.2μA.
BIAS
1
). See Table 1 for R
RS+
contributes to the input voltage off-
MAX9938
R
SENSE
C
IN
GND
RS-
R
IN
OUT
1
values at the dif-
LOAD
Placing RIN at the RS- input does not affect the gain
error of the device because the gain is given by the
ratio between R
Figure 2 shows the input common-mode filter.
Again, the corner frequency of the filter is determined
by the choice of R
In this case R
voltage. R
negligible effect on the device gain. If, for example, a fil-
ter with R
ing upon the gain selection, the gain error is affected by
either 2.5% (G = 25V/V, R
R
(G = 200V/V, R
Figure 2. Input Common-Mode Filter
1
= 200Ω) or 10% (G = 100V/V, R
IN
IN
= 10Ω and C
should be smaller than R
IN
1
OUT
= 100Ω).
C
affects both gain error and input offset
IN
IN
RS+
R
IN
, C
and R
IN
MAX9938
R
IN
SENSE
and is affected by R
1
1
= 1μF is built, then depend-
at RS+.
= 400Ω) or 5% (G = 50V/V,
GND
RS-
R
IN
C
OUT
IN
1
= 100Ω) or 10%
1
so that it has
1
.
LOAD