Datasheet

Detailed Description
The MAX44284 family features a single-supply; high-
accuracy unidirectional, current-sense amplifier in various
gain options and a -0.1V to 36V input common-mode
range that is independent of supply voltage (V
DD
). The
MAX44284 is ideal for many battery-powered, handheld
devices because it uses only maximum 31.2μA quiescent
supply current to extend battery life. The device’s low
input offset voltage, tight gain error, and low temperature
drift characteristics allow the use of small-sense resistors
for current measurements to improve power-supply con-
version efficiency and accuracy of measurements. This
feature allows monitoring of power-supply load current
even if the rail is shorted to ground. High-side current
monitoring does not interfere with the ground path of the
load being measured, making the IC particularly useful in
a wide range of high-reliability systems.
Because of its extended common-mode range below
ground, this part can also be used as a low-side current
sensing element.
Shutdown
The MAX44284 features active-low logic shutdown input
to reduce the supply current. Drive SHDN high for normal
operation. Drive SHDN low to place the device in shut-
down mode. In shutdown mode, the supply current drawn
from the V
DD
is less than 1μA (max).
Precision
The MAX44284 uses capacitive-coupled Instrumentation
amplifier architecture that enables the part to achieve
over the top common-mode voltage ranges, high power
efficiency, high gain accuracy, and low-power design.
Low Offset Voltage and Low Gain Error
The MAX44284 utilizes Capacitive-Coupled Chopper
Instrumentation Amplifier (CCIA) architecture to achieve
a low-input offset voltage of less than 10µA. These tech-
niques also enable extremely low-input offset voltage drift
over time and temperature to 50nV/°C. The precision V
OS
specification allows accurate current measurements with
lower values of current-sense resistors, thus reducing
power dissipation in battery-powered systems, as well as
load regulation issues in low-voltage DC power supplies.
Working with error tolerances with very few internal
blocks in this architecture is instrumental in achieving a
gain error of less than 0.20% over the entire temperature
range of -40°C to +125°C.
Applications Information
Input Differential Signal Range
The MAX44284’s input structure is optimized for sens-
ing small differential signals as low as 3.4mV full scale
(V
FS
) for high efficiency with lowest power dissipation in
the sense resistor, or 110mV full scale for high dynamic
range. The input differential signal range is determined
by the following equation for the MAX44248 family.
( )
DD
SENSE RANGE
V
V
GAIN
=
The input differential voltage range is estimated for
V
DD
from 1.7V to 5.5V for different gain values of the
MAX44284 as shown in Table 1
Ideally, the maximum load current develops the full-scale
sense voltage across the current-sense resistor. Choose
the gain needed to yield the maximum output voltage
required for the application:
OUT SENSE
V GAIN V= ×
Choosing the Sense Resistor
Voltage Loss
A high R
SENSE
value causes the power-source voltage
to drop due to IR loss. For minimal voltage loss, use the
lowest R
SENSE
value.
Accuracy
Use the below linear equation to calculate total error:
( )
( )
OUT SENSE OS
V GAIN GE V GAIN V= ±× ± ×
Table 1. V
SENSE
Input Range
PART GAIN (V/V) V
SENSE
RANGE (mV) with V
DD
(1.7V) V
SENSE
RANGE (mV) with V
DD
(5.5V)
MAX44284F 50 34 110
MAX44284H 100 17 55
MAX44284W 200 8.5 27.5
MAX44284E 500 3.4 11
MAX44284 36V, Input Common-Mode, High-Precision,
Low-Power Current-Sense Amplier
www.maximintegrated.com
Maxim Integrated │ 10