MAX9938 Maxim, MAX9938 Datasheet - Page 6

• 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 unidirectional high-side, current-sense
amplifier features a 1.6V to 28V input common-mode
range. This feature allows the monitoring of current out
of a battery with a voltage as low as 1.6V. The
MAX9938 monitors current through a current-sense
resistor and amplifies the voltage across that resistor.
The MAX9938 is a unidirectional current-sense amplifier
that has a well-established history. An op amp is used
to force the current through an internal gain resistor at
RS+, which has a value of R
equals the voltage drop across an external sense resis-
tor, R
Table 1. Internal Gain Setting Resistors (Typical Values)
6
_______________________________________________________________________________________
SENSE
V
BATT
. There is an internal resistor at RS- with the
= 1.6V TO 28V
GAIN (V/V)
200
100
50
25
Detailed Description
1
, such that its voltage drop
I
LOAD
R
OUT
P
10kΩ
GND
RS+
R
1
R
SENSE
R
1
MAX9938
RS-
R
100
100
200
400
1
(Ω)
same value as R
rent through R
FET. Its source current is the same as its drain current,
which flows through a second gain resistor, R
produces an output voltage, V
I
based on the matching of the two gain resistors R
R
MAX9938T, 50V/V for the MAX9938F, 100V/V for the
MAX9938H, and 200V/V for the MAX9938W. The output
is protected from input overdrive by use of an output
current limiting circuit of 7mA (typical) and a 6V clamp
protection circuit.
LOAD
OUT
OUT
(see Table 1). Total gain = 25V/V for the
x R
SENSE
1
Typical Operating Circuit
is sourced by a high-voltage p-channel
1
V
x R
DD
to minimize offset voltage. The cur-
= 3.3V
ADC
OUT
μC
/R
1
OUT
. The gain accuracy is
R
OUT
, whose magnitude is
20
10
10
10
(kΩ)
LOAD
OUT
1
. This
and