AD7298
Rev. B | Page 7 of 24
PIN CONFIGURATION AND FUNCTION DESCRIPTION
14
13
12
1
3
4
DOUT
15
SCLK
DIN
T
SENSE
_BUSY
11
CS
V
IN3
V
IN5
2
V
IN4
V
IN6
5
V
IN7
7
V
REF
6
GND1
8
D
CAP
9
GND
10
V
DD
19
V
IN1
20
V
IN2
18
V
IN0
17
PD/RS
16
V
DRIVE
AD7298
TOP VIEW
(Not to Scale)
08754-003
NOTES
1. THE EXPOSED METAL PADDLE ON THE BOTTOM
OF THE LFCSP PACKAGE SHOULD BE SOLDERED
TO PCB GROUND FOR PROPER FUNCTIONALITY
AND HEAT DISSIPATION.
Figure 2. Pin Configuration
Table 5. Pin Function Descriptions
Pin No. Mnemonic Description
1 to 5,
18 to 20
V
IN3
, V
IN4
,
V
IN5
, V
IN6
,
V
IN7
, V
IN0
,
V
IN1
, V
IN2
Analog Inputs. The AD7298 has eight single-ended analog inputs that are multiplexed into the on-chip track-
and-hold. Each input channel can accept analog inputs from 0 V to 2.5 V. Any unused input channels should be
connected to GND1 to avoid noise pickup.
6 GND1
Ground. Ground reference point for the internal reference circuitry on the AD7298. The external reference signals
and all analog input signals should be referred to this GND1 voltage. The GND1 pin should be connected to the
GND plane of a system. All ground pins should ideally be at the same potential and must not be more than 0.3 V
apart, even on a transient basis. The V
REF
pin should be decoupled to this ground pin via a 10 F decoupling
capacitor.
7 V
REF
Internal Reference/External Reference Supply. The nominal internal reference voltage of 2.5 V appears at this pin.
Provided the output is buffered, the on-chip reference can be taken from this pin and applied externally to the
rest of a system. Decoupling capacitors should be connected to this pin to decouple the reference buffer. For
best performance, it is recommended to use a 10 F decoupling capacitor on this pin to GND1. The internal
reference can be disabled and an external reference supplied to this pin, if required. The input voltage range for
the external reference is 2.0 V to 2.5 V.
8 D
CAP
Decoupling Capacitor Pin. Decoupling capacitors (1 F recommended) are connected to this pin to decouple the
internal LDO.
9 GND
Ground. Ground reference point for all analog and digital circuitry on the AD7298. The GND pin should be
connected to the ground plane of the system. All ground pins should ideally be at the same potential and must
not be more than 0.3 V apart, even on a transient basis. Both D
CAP
and V
DD
pins should be decoupled to this
GND pin.
10 V
DD
Supply Voltage, 2.8 V to 3.6 V. This supply should be decoupled to GND with 10 µF and 100 nF decoupling
capacitors.
11
CS
Chip Select, Active Low Logic Input. This pin is edge triggered on the falling edge of this input, the track-and-
hold goes into hold mode, and a conversion is initiated. This input also frames the serial data transfer. When CS
is
low, the output bus is enabled, and the conversion result becomes available on the DOUT output.
12 T
SENSE
_BUSY
Busy Output. This pin transitions high when a temperature sensor conversion starts and remains high until the
conversion completes.
13 DIN
Data In, Logic input. Data to be written to the AD7298 control register is provided on this input and is clocked
into the register on the falling edge of SCLK.
14 DOUT
Serial Data Output. The conversion result from the AD7298 is provided on this output as a serial data stream. The
bits are clocked out on the falling edge of the SCLK input. The data stream from the AD7298 consists of four
address bits indicating which channel the conversion result corresponds to, followed by the 12 bits of conversion
data (MSB first). The output coding is straight binary for the voltage channels and twos complement for the
temperature sensor result.
15 SCLK Serial Clock, Logic Input. A serial clock input provides the SCLK for accessing the data from the AD7298.
