AD7280AWBSTZ Analog Devices Inc, AD7280AWBSTZ Datasheet - Page 22

• Manufacturer Part Number: AD7280AWBSTZ
• Description: IC BATT MON LI-ION AUTO 48LQFP
• Manufacturer: Analog Devices Inc
• Series: -r

Specifications of AD7280AWBSTZ

• Function: Battery Monitor, Over/Under Voltage Protection
• Battery Chemistry: Lithium-Ion (Li-Ion)
• Voltage - Supply: 8 V ~ 30 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AD7280A
CONVERSION WINDOW
As described in the Converting Cell Voltages and Auxiliary
ADC Inputs section, the AD7280A converts the selected cell
voltage and auxiliary ADC inputs in a defined sequence (see
Figure 31). As described in the Circuit Information section,
the AD7280A consists primarily of a high voltage input multi-
plexer, a low voltage input multiplexer, and a SAR ADC. The six
cell voltage channels are presented to the ADC in turn by the high
voltage multiplexer. Control is then handed to the low voltage
multiplexer that allows the six auxiliary ADC channels to be
converted. Following completion of all selected conversions,
control is handed back to the high voltage multiplexer, and the
AD7280A is ready to receive the next valid convert start command.
The conversion window of the AD7280A includes the actual con-
version time for the selected channels (see Table 10), as well as
the additional time required to return control to the high
voltage multiplexer and configure it to start acquiring the cell
voltage between VIN6 and VIN5. The conversion window
defines the minimum time that should be allowed between
successive convert start commands.
The conversion window for the AD7280A can be calculated
using the following equation:
where Total Conversion Time can be calculated for either a
single device or for a chain of devices, as described in the
Converting Cell Voltages and Auxiliary ADC Inputs section.
SELF-TEST CONVERSION
A self-test conversion can be initiated on the AD7280A, which
allows the operation of the ADC and reference buffer to be
verified. The self-test conversion is completed on the internal
1.2 V band gap reference voltage, and the voltage range for the
conversion is 0 V to 5 V. The self-test conversion can be initi-
ated on either a single AD7280A or on all AD7280As in the
daisy chain simultaneously.
The conversion results can be read back though the read protocols
defined in the Serial Interface section. The self-test conversion
result typically varies between Code 970 and Code 990.
The self-test conversion can also be used to verify the operation
of the alert outputs, as described in the Alert Output section.
Conversion Window = Total Conversion Time + 80 μs
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CONNECTION OF FEWER THAN SIX VOLTAGE CELLS
The AD7280A provides six input channels for battery cell voltage
measurement. The AD7280A can also be used in applications
that require fewer than six voltage measurements. In these appli-
cations, care should be taken to ensure that the sum of the
individual cell voltages still exceeds the minimum V
voltage. For this reason, the recommended minimum number of
battery cells connected to each AD7280A is 4. Care should also
be taken to ensure that the voltage on the VIN6 input is always
greater than or equal to the voltage on the V
example, in an application with five battery cells connected to
the AD7280A, the cell voltage on Cell 5 should be applied across
VIN6 and VIN5, and the VIN4 and VIN5 inputs should be shorted
together. Figure 35 shows an example of the battery connections
to the AD7280A in a four-cell battery monitoring application.
Regardless of how many cell voltage measurements are required
in the user application, the AD7280A acquires and converts the
voltages on all six cell voltage input channels. The conversion data
on all six voltage channels is supplied to the DSP/microprocessor
using the SPI/daisy-chain interfaces. Users should ignore the
conversion data that is not required in their application.
It is also possible to read back a single cell voltage conversion
result from each device in the daisy chain. This can be done by
programming the read register on each device to read back the
required conversion result (see Example 4 in the Examples of
Interfacing with the AD7280A section). However, as previously
described, all six cell voltage channels are converted. When
using the device in this mode, the overall conversion sample
rate should be limited by the conversion window required for
the number of channels selected by Bits[D15:D14] of the
control register.
When using the alert function, the user should program the alert
register to ensure that the shorted channels do not incorrectly
trigger an alert output (see the Alert Output section).
Figure 35. Typical Connections for a Four-Cell Application
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
100nF
100nF
100nF
100nF
VIN6
VIN5
VIN4
VIN3
VIN2
VIN1
VIN0
AD7280A
DD
supply pin. For
DD
supply