Datasheet

Voltage Output (MAX9929F)
The output voltage equation for the MAX9929_ is given
below:
V
OUT
= (R
SENSE
x I
LOAD
) x (A
V
)
where V
OUT
= the desired full-scale output voltage,
I
LOAD
= the full-scale current being sensed, R
SENSE
=
the current-sense resistor, A
V
= MAX9929F voltage gain
(50V/V).
SIGN Output
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 sys-
tems, this is useful for determining whether the battery is
charging or discharging. The SIGN output might not cor-
rectly indicate the direction of load current when V
SENSE
is between -1.8mV to -1.2mV (see Figure 2). Comparator
hysteresis of 0.6mV prevents oscillation of SIGN output. If
current direction is not needed, leave SIGN unconnected.
Applications Information
Choosing R
SENSE
The MAX9928F/MAX9929F operate over a wide variety
of current ranges with different sense resistors. Adjust the
R
SENSE
value to monitor higher or lower current levels.
Select R
SENSE
using these guidelines:
● Voltage Loss: A high R
SENSE
value causes the
power-source voltage to drop due to IR loss. For least
voltage loss, use the lowest R
SENSE
value.
● Accuracy: A high R
SENSE
value allows lower cur-
rents to be measured more accurately. This is be-
cause offsets become less significant when the sense
voltage is larger.
● Efficiency and Power Dissipation: At high current
levels, the I
2
R losses in R
SENSE
might be significant.
Take this into consideration when choosing the resis-
tor value and power dissipation (wattage) rating. Also,
if the sense resistor is allowed to heat up excessively,
its value could drift.
● Inductance: If there is a large high-frequency compo-
nent to I
SENSE
, keep inductance low. Wire-wound re-
sistors have the highest inductance, while metal film
is somewhat better. Low-inductance metal-film resis-
tors are available. Instead of being spiral wrapped
around a core, as in metal film or wirewound resistors,
these are a straight band of metal. They are made in
values under 1Ω.
Use in Systems with Super Capacitors
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 systems use
multifarad (1F–50F) capacitor banks to supply enough
energy to keep critical systems alive even if the primary
power source is removed or temporarily disabled. Unlike
batteries, these capacitors can discharge all the way down
to 0V. The MAX9928/MAX9929 can continuously help
monitor their health and state of charge/discharge.
UCSP Applications Information
For the latest application details on UCSP construc-
tion, dimensions, tape carrier information, PCB tech-
niques, bump-pad layout, and recommended reflow
temperature profile, as well as the latest information
on reliability testing results, go to Maxim’s website at
www.maximintegrated.com/ucsp to find Application
Note 1891: Wafer-Level Packaging (WLP) and its
Applications.
Chip Information
PROCESS: BiCMOS
MAX9928/MAX9929 -0.1V to +28V Input Range, Micropower,
Uni-/Bidirectional, Current-Sense Ampliers
www.maximintegrated.com
Maxim Integrated │ 10