ADC121C021CIMKX/NOPB National Semiconductor, ADC121C021CIMKX/NOPB Datasheet - Page 28

• Manufacturer Part Number: ADC121C021CIMKX/NOPB
• Description: IC ADC 12BIT I2C ALERT TSOT-23-6
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of ADC121C021CIMKX/NOPB

• Number Of Bits: 12
• Sampling Rate (per Second): 188.9k
• Data Interface: I²C, Serial
• Number Of Converters: 1
• Power Dissipation (max): 780µW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6 Thin, TSOT-23-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ADC121C021CIMKX

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2.3 INTELLIGENT BATTERY MONITOR
The ADC121C021 is easily used as an intelligent battery
monitor. The simple circuit shown in
ADC121C021, the LP2980 fixed reference, and a resistor di-
vider to implement an intelligent battery monitor with a window
supervisory feature. The window supervisory feature is im-
plemented by the "out of range" alert function. When the
battery is recharging, the Over Range Alert will indicate that
the charging cycle is complete (see
battery is nearing depletion, the Under Range Alert will indi-
cate that the battery is low (see
In addition to the window supervisory feature, the
ADC121C021 will allow the controller to read the battery volt-
age at any time during operation.
FIGURE 20. Intelligent Battery Monitor Circuit
FIGURE 22. Discharge Cycle
FIGURE 21. Recharge Cycle
Figure
Figure
22).
Figure
21). When the
20, uses the
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The accurate voltage reading and the alert feature will allow
a controller to improve the efficiency of a battery-powered
device. During the discharge cycle, the controller can switch
to a low-battery mode, safely suspend operation, or report a
precise battery level to the user. During the recharge cycle,
the controller can implement an intelligent recharge cycle,
decreasing the charge rate when the battery charge nears
capacity.
2.3.1 Trickle Charge Controller
While a battery is discharging, the ADC121C021 can be used
to control a trickle charge to keep the battery near full capacity
(see
will recharge. An intelligent recharge cycle will prevent over-
charging and damaging the battery. With a trickle charge, the
battery powered device can be disconnected from the charger
at any time with a full charge.
2.4 LAYOUT, GROUNDING, AND BYPASSING
For best accuracy and minimum noise, the printed circuit
board containing the ADC121C021 should have separate
analog and digital areas. The areas are defined by the loca-
tions of the analog and digital power planes. Both of these
planes should be located on the same board layer. A single,
solid ground plane is preferred if digital return current does
not flow through the analog ground area. Frequently a single
ground plane design will utilize a "fencing" technique to pre-
vent the mixing of analog and digital ground current. Separate
ground planes should only be utilized when the fencing tech-
nique is inadequate. The separate ground planes must be
connected in one place, preferably near the ADC121C021.
Special care is required to guarantee that signals do not pass
over power plane boundaries. Return currents must always
have a continuous return path below their traces.
The ADC121C021 power supply should be bypassed with a
4.7µF and a 0.1µF capacitor as close as possible to the device
with the 0.1µF right at the device supply pin. The 4.7µF ca-
pacitor should be a tantalum type and the 0.1µF capacitor
should be a low ESL type. The power supply for the
ADC121C021 should only be used for analog circuits.
Avoid crossover of analog and digital signals and keep the
clock and data lines on the component side of the board. The
clock and data lines should have controlled impedances.
Figure
23). When the alert output is active, the battery
FIGURE 23. Trickle Charge
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