Datasheet

The ultra-low V
OS
of the MAX4208/MAX4209 allows
full-scale V
SENSE
of only 10mV to 20mV for minimally
invasive current sensing using milliohm sense resistors
to get high accuracy. Previous methods used the internal
resistance of the inductor in the step-down DC-DC con-
verter to measure the current, but the accuracy was only
20% to 30%. Using a full-scale V
SENSE
of 20mV, a 20μV
max, V
OS
error term is less than 0.1% and MAX4209H
gain error is 0.25% max at 100x, so the total accuracy is
greatly improved. The 0 to 2V output of MAX4209H can
be sent to an ADC for calculation. The adjustable gain
of MAX4208, can be set to a gain of 250x using 1kΩ
and 249kΩ resistors, to scale up a lower 10mV V
SENSE
voltage to a larger 2.5V output voltage for wider dynamic
range as needed.
Figure 5. MAX4208/MAX4209 Used as Precision Current-Sense Amplifiers for Notebook Computers with V
SENSE
of 20mV
ASIC
IN+
IN-
REF
V
SS
V
DD
REFIN/MODE
1V AT 10A
ADC
ANTI-ALIASING
FILTER
0.002Ω
+V
SENSE
-
MAX4209H
OUT
+3.3V
V
SENSE
= 10A x 0.002Ω = 20mV
POWER IN R
SENSE
= 10A x 20mV = 200mW
OUT = G x 20mV = 100 x 20mV = 2V
IN-
IN+
REFIN/MODE
REF
FB
MAX4208
R4
R3
V
DD
V
SS
C
FB
5V
OUT
REF
R2
FB
R1
G = 1 +
R2
R1
BUFFER OUT =
V
DD
/2
V
DD
/2
MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision
Instrumentation Ampliers with REF Buffer
www.maximintegrated.com
Maxim Integrated │ 15
Typical Application Circuit