Datasheet

External Reference (MAX4072)
The MAX4072 contains REFIN pin for external refer-
ence voltage. The allowable voltage range on REFIN is
1V (min) to 4V (max) with V
CC
≥ 5.1V.
Reference Output
(MAX4069/MAX4060/MAX4071)
The REFOUT of the MAX4069/MAX4070/MAX4071 can
sink 100µA and source 500µA. Keep the total capaci-
tance on REFOUT under 500pF to maintain stability.
Recommended Component Values
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:
V
OUT
= V
SENSE
x A
V
where V
SENSE
is the full-scale sense voltage, 75mV for
gain of 50V/V, or 50mV for gain of 100V/V. A
V
is the
gain of the device.
In applications monitoring high current, ensure that
R
SENSE
is able to dissipate its own I
2
R loss. If the resis-
tor’s power dissipation is exceeded, its value may drift
or it may fail altogether, causing a differential voltage
across the terminals in excess of the absolute maxi-
mum ratings. Use resistors specified for current- sens-
ing applications.
The MAX4069–MAX4072 sense a wide variety of cur-
rents with different sense-resistor values. Table 1 lists
common resistor values for typical operation of these
devices. Listed output voltage is with respect to REF.
Sense Resistor, R
SENSE
Choose R
SENSE
based on the following criteria:
Voltage Loss: A high R
SENSE
value causes the power-
source voltage to degrade through IR loss. For minimal
voltage loss, use the lowest R
SENSE
value.
Accuracy: A high R
SENSE
value allows lower currents
to be measured more accurately. This is because off-
sets become less significant when the sense voltage is
larger. For best performance, select R
SENSE
to provide
approximately 75mV (gain of 50V/V) or 50mV (gain of
100V/V) of sense voltage for the full-scale current in
each application.
Efficiency and Power Dissipation: At high-current lev-
els, the I
2
R losses in R
SENSE
can be 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.
Inductance: Keep inductance low if I
SENSE
has a large
high-frequency component. Wire-wound resistors have
the highest inductance, while metal film is somewhat
better. Low-inductance metal-film resistors are also
available. Instead of being spiral-wrapped round a
Bidirectional, High-Side, Current-Sense
Amplifiers with Reference
MAX4070
I
DISCHARGE
R
SENSE
I
CHARGE
LOAD
TO ADC
2.5V
V
CC
GSEL
GND
RS- RS+
REFOUT
OUT
SHDN
2
CELLS
-25mV 25mV 50mV0
DISCHARGE
CURRENT
CHARGE
CURRENT
-2.5V
5V
2.5V
A
V
= 100
V
OUT
- V
REF
V
SENSE
Figure 2. Bidirectional Current Monitor
MAX4069–MAX4072
Maxim Integrated
11