MAX9938F Ver la hoja de datos (PDF) - Maxim Integrated
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MAX9938F Datasheet PDF : 14 Pages
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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- (R1). See Table 1 for R1 values at the dif-
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 IBIAS contributes to the input voltage off-
set. IBIAS is typically 0.2μA.
Placing RIN at the RS- input does not affect the gain
error of the device because the gain is given by the
ratio between ROUT and R1 at RS+.
Figure 2 shows the input common-mode filter.
Again, the corner frequency of the filter is determined
by the choice of RIN, CIN and is affected by R1.
In this case RIN affects both gain error and input offset
voltage. RIN should be smaller than R1 so that it has
negligible effect on the device gain. If, for example, a fil-
ter with RIN = 10Ω and CIN = 1μF is built, then depend-
ing upon the gain selection, the gain error is affected by
either 2.5% (G = 25V/V, R1 = 400Ω) or 5% (G = 50V/V,
R1 = 200Ω) or 10% (G = 100V/V, R1 = 100Ω) or 10%
(G = 200V/V, R1 = 100Ω).
RSENSE
RIN
CIN
RS+
RS-
OUT
MAX9938
GND
LOAD
Figure 1. Differential Input Filter
RSENSE
RIN
RIN
CIN
CIN
RS+
RS-
OUT
MAX9938
GND
Figure 2. Input Common-Mode Filter
LOAD
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