Preliminary Technical Data
AD7280
21
CS
Chip select Input. When acting as a master, that is the Master pin of the AD7280 is connected to VDD, the CS
input is used to frame the input and output data on the SPI. The CS input also frames the input and output data
on the Daisy Chain Interface when the MASTER input of the AD7280 is connected to VSS.
22
23
SCLK
SDI
Serial Clock Input. When acting as master the SCLK input is supplied from the DSP/uP. When acting as a slave on
the Daisy Chain this input should be connected to the SCLKhi output of the AD7280 immediately below it in
potential in the Daisy Chain.
Serial Data Input. Data to be written to the on-chip registers is provided on this input and is clocked into the
AD7280 on the falling edge of SCLK. When acting as master this is the data input of the SPI interface. When
acting as a slave on the Daisy Chain this input acepts data from the SDOhi output of the AD7280 immediately
below it in potential in the Daisy Chain.
24
25
CNVST
SDOlo
Convert Start Input. The conversion is initiated on the falling edge of CONVST. When acting as master the
CNVST pulse is supplied from the DSP/uP. When acting as a slave on the Daisy Chain this input should be
connected to the CNVSThi output of the AD7280 immediately below it in potential in the Daisy Chain. This
input can also be tied to VCC and the conversion initiated through the serial interface.
Serial Data Output in Daisy Chain mode. When configured as a slave device this output should be connected to
the SDIhi input of the AD7280 immediately below it in potential on the Daisy Chain. The data from each
AD7280 in the Daisy Chain will be passed through the SDOlo outputs and SDIhi inputs of each AD7280 in the
chain and supplied to the uP/DSP through the SDO output of the master AD7280. When configured as a master
device it is recommended that this output, which is not required in slave mode, be connected to VSS either
directly or through a pull-down 1kOhm resistor.
26
SDO
Serial Data Output. The conversion output data or the register output data is supplied to this pin as a serial data
stream. The bits are clocked out on the rising edge of the SCLK input, and 32 SCLKs are required to access the
data. The data is provided MSB first. In a Daisy Chain application the SDO output of the master AD7280 should
be connected to the uP/DSP. The SDO outputs of the remaining AD7280s in the chain should be terminated to
V
SS through a 1kΩ resistor. The data from each AD7280 in the Daisy Chain will be passed through the SDOlo
outputs and SDIhi inputs of each AD7280 in the chain and supplied to the uP/DSP through the SDO output of
the master AD7280. 32 SCLKs are required for each AD7280 in the chain to access the data.
27
28
ALERT
Digital Output. Flag to indicate over voltage, under voltage, over temperature or under temperature. The ALERT
output of the master AD7280 should be connected to the uP/DSP. The ALERT outputs of the remaining
AD7280s in the chain should be be terminated to VSS through a 1kΩ resistor.
Alert Output in Daisy Chain mode. The alert signal from each AD7280 in the Daisy Chain will be passed through
the ALERTlo outputs and ALERThi inputs of each AD7280 in the chain and supplied to the uP/DSP through the
ALERT output of the master AD7280. When configured as a slave device this output should be connected to the
ALERThi input of the AD7280 immediately below it in potential on the Daisy Chain. When configured as a
master device it is recommended that this output, which is not required in slave mode, be connected to VSS
either directly or through a pull-down 1kOhm resistor.
ALERTlo
29
30
VDRIVE
Logic Power Supply Input. The voltage supplied at this pin determines at what voltage the interface operates.
This pin should be decoupled to DGND. The voltage range on this pin is 2.7 V to 5.25 V and may be different to
the voltage at AVCC and DVCC, but should never exceed either by more than 0.3 V.
Analog Supply Voltage, 4.75 V to 5.25 V. This is the supply voltage for the ADC core. The AVCC and DVCC voltages
should ideally be at the same potential. For best performance, it is recommended that the DVCC and AVCC pins
be shorted together, to ensure that the voltage difference between them never exceeds 0.3 V even on a
transient basis. This supply should be decoupled to AGND. Place 100 nF decoupling capacitors on the AVCC pin.
The AVCC supply pin should be externally connected to the VREG output.
AVCC
31
AGND
Analog Ground. Ground reference point for all analog circuitry on the AD7280. This input should be at the
same potential as the base of the series connected battery cells. The AGND and DGND voltages ideally should
be at the same potential and must not be more than 0.3 V apart, even on a transient basis.
32
33 to 38
39
VTTERM
VT6 to VT1
CREF
Thermistor termination resistor input.
Voltage temperature input from potential divider with thermistor.
A 100 nF decoupling capacitor to REFGND should be placed on this pin.
40
VREF
Reference Output. The on-chip reference is availble on this pin for use external to the AD7280. The nominal
internal reference voltage is 2.5V, which appears at the pin. A 10 µF decoupling capacitor to REFGND is
recommended on this pin.
41
42
REFGND
ALERThi
Reference Ground. This is the ground reference point for the internal bandgap reference circuitry on the
AD7280. The REFGND voltage should be at the same potential as the AGND voltage.
Alert Input in Daisy Chain mode. Flag to indicate over voltage, under voltage, over temperature or under
temperature in Daisy Chain mode. The alert signal from each AD7280 in the Daisy Chain will be passed through
the ALERTlo outputs and ALERThi inputs of each AD7280 in the chain and supplied to the uP/DSP through the
ALERT output of the master AD7280. This input should be connected to the ALERTlo output of the AD7280
immediately above it in potential on the Daisy Chain. When this pin is unused,it is recommended that it is
connected to VDD through a 1kOhm resistor.
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