MAX9929F Maxim, MAX9929F Datasheet - Page 10

• Manufacturer Part Number: MAX9929F
• Description: The MAX9928F/MAX9929F low-cost, uni-/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 output voltage equation for the MAX9929_ is given
below:
where V
I
the current-sense resistor, A
gain (50V/V).
The current/voltage at OUT indicates magnitude. The
SIGN output indicates the current’s direction. The SIGN
comparator compares RS+ to RS-. The sign output is
high when RS+ is greater than RS- indicating positive
current flow. The sign output is low when RS- is greater
than RS+ indicating negative current flow. In battery-
operated systems, this is useful for determining
whether the battery is charging or discharging. The
SIGN output might not correctly indicate the direction of
load current when V
(see Figure 2). Comparator hysteresis of 0.6mV pre-
vents oscillation of SIGN output. If current direction is
not needed, leave SIGN unconnected.
The MAX9928F/MAX9929F operate over a wide variety
of current ranges with different sense resistors. Adjust
the R
els. Select R
• Voltage Loss: A high R
• Accuracy: A high R
• Efficiency and Power Dissipation: At high current
-0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Amplifiers
10
LOAD
power-source voltage to drop due to IR loss. For
least voltage loss, use the lowest R
rents to be measured more accurately. This is
because offsets become less significant when the
sense voltage is larger.
levels, the I
Take this into consideration when choosing the resis-
______________________________________________________________________________________
SENSE
= the full-scale current being sensed, R
OUT
V
value to monitor higher or lower current lev-
SENSE
OUT
= the desired full-scale output voltage,
2
R losses in R
Applications Information
= (R
using these guidelines:
Voltage Output (MAX9929F)
SENSE
SENSE
SENSE
is between -1.8mV to -1.2mV
SENSE
x I
SENSE
V
value allows lower cur-
LOAD
= MAX9929F voltage
Choosing R
might be significant.
) x (A
value causes the
SENSE
SIGN Output
V
)
value.
SENSE
SENSE
=
• Inductance: If there is a large high-frequency com-
Since the input common-mode voltage range of the
MAX9928/MAX9929 extends all the way from -0.1V to
28V, they are ideal to use in applications that require
use of super capacitors for temporary or emergency
energy storage systems. Some modern industrial and
automotive systems use multifarad (1F–50F) capacitor
banks to supply enough energy to keep critical sys-
tems alive even if the primary power source is removed
or temporarily disabled. Unlike batteries, these capaci-
tors can discharge all the way down to 0V. The
MAX9928/MAX9929 can continuously help monitor their
health and state of charge/discharge.
For the latest application details on UCSP construction,
dimensions, tape carrier information, PCB techniques,
bump-pad layout, and recommended reflow tempera-
ture profile, as well as the latest information on reliability
testing results, go to Maxim’s website at www.maxim-
ic.com/ucsp to find Application Note 1891:
Understanding the Basics of the Wafer-Level Chip-
Scale Package (WL-CSP).
PROCESS: BiCMOS
tor value and power dissipation (wattage) rating.
Also, if the sense resistor is allowed to heat up exces-
sively, its value could drift.
ponent to I
resistors have the highest inductance, while metal
film is somewhat better. Low-inductance metal-film
resistors are available. Instead of being spiral
wrapped around a core, as in metal film or wire-
wound resistors, these are a straight band of metal.
They are made in values under 1Ω.
UCSP Applications Information
Use in Systems with Super Capacitors
SENSE
, keep inductance low. Wire-wound
Chip Information