MAX4072 Maxim, MAX4072 Datasheet - Page 10

• Manufacturer Part Number: MAX4072
• Description: The MAX4069–MAX4072 low-cost, bidirectional, high-side, current-sense amplifiers are ideal for monitoring battery charge and discharge currents in notebooks, cell phones, and other portable equipment
• Manufacturer: Maxim

The MAX4069–MAX4072 bidirectional, high-side, cur-
rent-sense amplifiers are ideal for portable equipment.
The wide 1.35V to 24V input common-mode voltage
range is independent of the supply voltage, ensuring
that the current-sense feedback remains accurate even
when connected to a battery pack in deep discharge.
The MAX4069/MAX4071/MAX4072 operate from a 2.7V
to 24V single supply. Because the MAX4070 has a 2.5V
internal reference, it operates from 3.6V to 24V. All
devices have a low 100µA supply current that reduces
to only 10µA (typ) in shutdown mode. To achieve maxi-
mum flexibility, an external current-sense resistor is
used along with a gain select pin (GSEL) to choose
either 50V/V or 100V/V. Drive GSEL low to select gain of
50V/V or drive GSEL high to choose gain of 100V/V
(see Functional Diagram ). The MAX4069 has an
adjustable reference voltage set by two external resis-
tors between REFOUT and ADJ, and GND pins. The
MAX4070 contains an internal 2.5V reference. The
MAX4071 is similar to the MAX4070 but with a fixed
internal reference voltage of 1.5V. The MAX4072 has a
reference input pin to allow use of external references.
Charging current is represented by an output voltage
from the reference voltage to V
rent is given from the reference voltage to GND. The
direction of V
The input stage of the MAX4069–MAX4072 is shown in
Figure 1. Its unique topology allows for monitoring bidi-
rectional currents through the sense resistor (R
for instance, current flows from RS+ to RS-, the
MAX4069–MAX4072 match for the voltage drop over the
external sense resistor (R
rent through the internal Q1 and RG1. At the same time,
the current through Q2 and RG2 decreases, however,
internal circuitry not shown in Figure 1 prevents Q2 from
turning off completely. Likewise, if current flows from RS-
to RS+, the current through Q2 and RG2 increases and
the current through Q1 decreases. In this way, the volt-
ages at the input terminals of the internal amplifier A1 are
kept constant and an accurate measurement of the sense
voltage is achieved. In the following amplifier stages of
the MAX4069–MAX4072, the output signal of amplifier A2
is level-shifted towards the reference voltage (V
resulting in a voltage at the output pin (OUT) that swings
above the V
below V
Bidirectional, High-Side, Current-Sense
Amplifiers with Reference
Note: R
10
______________________________________________________________________________________
G1
REF
= R
for negative-sense voltages.
REF
SENSE
G2
= 104k (typ).
voltage for positive-sense voltages and
is totally arbitrary.
Detailed Description
SENSE
CC
) by increasing the cur-
, while discharge cur-
SENSE
REF
). If,
),
Systems such as laptop computers and other devices
that have internal charge circuitry require a precise bidi-
rectional, current-sense amplifier to accurately monitor
the battery’s current regardless of polarity. Figure 2
shows the MAX4069–MAX4072 used as a bidirectional
current monitor. In Figure 2, the direction of V
assigned to charge and discharge, assuming charge is
greater than discharge. The practical choice of direction
is based on dynamic range at OUT, given that the range
of REF to V
ground. This is useful for implementing either smart bat-
tery packs or fuel gauges.
The MAX4069–MAX4072 can achieve high-current
measurements by using low-value sense resistors,
which can be paralleled to further increase the current-
sense limit.
The MAX4069 has an output reference voltage that can
be set to a desired voltage by a two-resistor divider
between REFOUT, ADJ, and GND. If REFOUT and ADJ
are connected together, the minimum output reference
voltage is obtained, 1.23V (typ). The maximum voltage
for REFOUT is 4V (that requires V
ommended range for the external resistors is: R1 + R2
should be > 20kΩ and < 500kΩ.
Figure 1. Detailed Input Stage
Bidirectional, Current-Sense Amplifier
Q1
High-Current Measurement
CC
RG1
RS+
Applications Information
is usually greater than from REF to
R
Adjusting V
SENSE
A1
RS-
RG2
MAX4069–MAX4072
Q2
CC
REF
OUT
≥ 5.1V). The rec-
A2
(MAX4069)
I
OUT
SENSE
is