AD7280AWBSTZ Analog Devices Inc, AD7280AWBSTZ Datasheet - Page 15

• 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

THEORY OF OPERATION
CIRCUIT INFORMATION
The AD7280A is a lithium ion (Li-Ion) battery monitoring chip
that can monitor the voltage and temperature of four, five, or six
series-connected Li-Ion battery cells. The AD7280A also provides
an interface that can be used to control external transistors for
cell balancing.
The V
be taken from battery cells being monitored by the part. An
internal V
and the internal interface circuitry. This V
on an output pin for use external to the AD7280A.
The AD7280A consists of a high voltage input multiplexer, a low
voltage input multiplexer, and a SAR ADC. The high voltage
multiplexer allows four, five, or six series-connected Li-Ion
battery cells to be measured. The low voltage multiplexer provides
the user with six single-ended ADC inputs that can be used in
combination with external thermistors to measure the tempera-
ture of each battery cell. The auxiliary ADC inputs can also be
used for external diagnostics in the application. Initiating conver-
sions on all 12 channels, that is, the six cell voltage channels and
the six auxiliary ADC channels, requires only a single CNVST
pulse. Alternatively, the conversion can be initiated through the
rising edge of CS . Each conversion result is stored in an individual
result register (see
Each individual cell voltage and auxiliary ADC measurement
requires a minimum of 1 μs to acquire and complete a conver-
sion. Depending on the external components connected to the
analog inputs of the AD7280A, additional acquisition time may
be required. A higher acquisition time can be selected through
the control register. The AD7280A also provides a conversion
averaging option that can be selected through the control register.
This option allows the user to complete two, four, or eight averages
on each cell voltage and auxiliary ADC measurement. The aver-
aged conversion results are stored in the result registers. On
power-up, the default combined acquisition and conversion
time is 1 μs, with the averaging register set to 0, that is, a single
conversion per channel.
The results of the cell voltage and auxiliary ADC conversions
are read back via the 4-wire serial peripheral interface (SPI).
The SPI is also used to write to and read from the internal
registers.
The AD7280A features an alert function that can be triggered if
the voltage conversion results or the auxiliary ADC conversion
results exceed the maximum and minimum voltage thresholds
selected by the user. The alert modes and threshold levels are
selected by writing to internal registers.
DD
and V
REG
rail is generated to provide power for the ADC
SS
supplies required by the AD7280A should
Table 13
).
REG
voltage is available
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The AD7280A provides six analog output voltages that can be
used to control external transistors as part of a cell balancing
circuit. Each cell balance output provides a 0 V or 5 V voltage,
with respect to the potential on the base of each individual cell,
that can be applied to the gate of the external cell balancing
transistors.
The AD7280A features a daisy-chain interface. Individual
AD7280A devices can monitor the cell voltages and tempera-
tures of six cells. A chain of AD7280As can be used to monitor
the cell voltages and temperatures of a larger number of cells. The
conversion data from each AD7280A in the chain passes to the
system controller via a single SPI interface. Control data can
similarly be passed via the SPI up the chain to each individual
AD7280A.
The AD7280A includes an on-chip 2.5 V reference. The
reference voltage is available for use external to the AD7280A.
The AD7280A also has a V
which the serial interface operates. V
easily interface to both 3 V and 5 V processors. For example, in
the recommended configuration, the AD7280A is operated with
a supply of 5 V; however, the V
a 3 V supply, allowing a large dynamic range with low voltage
digital processors.
CONVERTER OPERATION
The conversion paths of the AD7280A consist of a high voltage
input multiplexer or a low voltage input multiplexer and a SAR
ADC. The high voltage multiplexer selects the pair of analog
inputs, VIN0 to VIN6, that is to be converted. The voltage of
each individual cell is measured by converting the difference
between adjacent analog inputs, that is, VIN1 − VIN0, VIN2 −
VIN1, and so on (see Figure 22 and Figure 23). The low voltage
multiplexer selects the auxiliary ADC input, AUX1 to AUX6,
that is to be converted. The conversion results for each cell
voltage and auxiliary ADC input can be accessed t
the programmed conversion sequence is completed.
Figure 22. Mux Configuration During VIN1 to VIN0 Sampling
VIN6
VIN5
VIN4
VIN3
VIN2
VIN1
VIN0
DRIVE
DRIVE
feature to control the voltage at
pin can be powered from
DRIVE
allows the ADC to
AD7280A
WAIT
ADC V
ADC V
after
IN+
IN–