max9938feuk Maxim Integrated Products, Inc., max9938feuk Datasheet - Page 7

• Manufacturer Part Number: max9938feuk
• Description: 1?a, 4-bump Ucsp/sot23,
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9938 is unique since the supply voltage is the
input common-mode voltage (the average voltage at
RS+ and RS-). There is no separate V
pin. Therefore, the OUT voltage swing is limited by the
minimum voltage at RS+.
and
V
minimum RS+ voltage. For best performance with a
3.6V supply voltage, select R
mately 120mV (gain of 25V/V), 60mV (gain of 50V/V), or
30mV (gain of 100V/V) of sense voltage for the full-
scale current in each application. These can be
increased by use of a higher minimum input voltage.
In the linear region (V
components to accuracy: input offset voltage (V
gain error (GE). For the MAX9938, V
and gain error is 0.5% (max). Use the linear equation:
to calculate total error. A high R
currents to be measured more accurately because off-
sets are less significant when the sense voltage is larger.
SENSE
V
V
OUT
OUT
full scale should be less than V
(max) = V
= (gain ± GE) x V
R
SENSE
_______________________________________________________________________________________
RS+
OUT Swing vs. V
OUT
=
(min) - V
G I
< V
×
V
SENSE
OUT
SENSE
LOAD
OUT(max)
SENSE
SENSE
(max)
Precision Current-Sense Amplifier
(max)
± (gain x V
to provide approxi-
OS
CC
value allows lower
RS+
(max) - V
), there are two
OUT
= 500μV (max)
supply voltage
and V
/gain at the
Accuracy
OS
OS
OH
SENSE
)
) and
1µA, 4-Bump UCSP/SOT23,
At high current levels, the I
significant. Take this into consideration when choosing
the resistor value and its power dissipation (wattage)
rating. Also, the sense resistor’s value might drift if it is
allowed to heat up excessively. The precision V
the MAX9938 allows the use of small sense resistors to
reduce power dissipation and reduce hot spots.
Because of the high currents that flow through R
take care to eliminate parasitic trace resistance from
causing errors in the sense voltage. Either use a four-
terminal current-sense resistor or use Kelvin (force and
sense) PCB layout techniques.
When designing a system that uses a sample-and-hold
stage in the ADC, the sampling capacitor momentarily
loads OUT and causes a drop in the output voltage. If
sampling time is very short (less than a microsecond),
consider using a ceramic capacitor across OUT and
GND to hold V
decreases the small-signal bandwidth of the current-
sense amplifier and reduces noise at OUT.
Optional Output Filter Capacitor
OUT
constant during sampling. This also
Efficiency and Power Dissipation
2
R losses in R
Kelvin Connections
SENSE
can be
SENSE
OS
of
7
,