ADC081C027CIMK Datasheet, PDF (32/41 Pages) National Semiconductor (TI) – ADC081C021/ADC081C027 I2C-Compatible, 8-Bit Analog-to-Digital Converter (ADC) with Alert Function

ADC081C021, ADC081C027
SNAS447C – FEBRUARY 2008 – REVISED MARCH 2013
www.ti.com
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.
Trickle Charge Controller
While a battery is discharging, the ADC081C021 can be used to control a trickle charge to keep the battery near
full capacity (see Figure 41). When the alert output is active, the battery 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.
Measured
Battery Voltage
V_LOW+V_HYST
V_LOW Limit
ALERT pin
(Active Low)
TIME
Figure 41. Trickle Charge
LAYOUT, GROUNDING, AND BYPASSING
For best accuracy and minimum noise, the printed circuit board containing the ADC081C021 should have
separate analog and digital areas. The areas are defined by the locations 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 prevent the mixing of analog and digital ground currents. Separate ground planes
should only be utilized when the fencing technique is inadequate. The separate ground planes must be
connected in one place, preferably near the ADC121C021. Special care is required to ensure that signals do not
pass over power plane boundaries. Return currents must always have a continuous return path below their
traces.
The ADC081C021 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 capacitor should be a tantalum type and the
0.1µF capacitor should be a low ESL type. The power supply for the ADC081C021 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.
32
Submit Documentation Feedback
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: ADC081C021 ADC081C027