AD7817/AD7818 Data Sheet
Rev. E | Page 8 of 20
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
BUSY
OTI
CS
V
IN1
REF
IN
AGND
ONVST
V
IN2
16
15
14
13
12
11
10
9
SCLK
D
IN
D
OUT
V
IN4
V
IN3
V
DD
DGND
RD/WR
AD7817
TOP VIEW
(Not to Scale)
01316-004
Figure 4. AD7817 Pin Configuration
Table 4. AD7817 Pin Function Descriptions
Pin
No. Mnemonic Description
1
CONVST
Logic Input Signal. The convert start signal. A 10-bit analog-to-digital conversion is initiated on the falling edge of this
signal. The falling edge of this signal places track-and-hold in hold mode. Track-and-hold goes into track mode again at
the end of the conversion. The state of the CONVST
signal is checked at the end of a conversion. If it is logic low, the
AD7817 powers down. See the Operating Modes section.
2 BUSY
Logic Output. The busy signal is logic high during a temperature or voltage A/D conversion. The signal can be used to
interrupt a microcontroller when a conversion has finished.
3
OTI
Logic Output. The overtemperature indicator (OTI) is set logic low if the result of a conversion on Channel 0
(temperature sensor) is greater that an 8-bit word in the overtemperature register (OTR). The signal is reset at the end
of a serial read operation, that is, a rising RD/WR
edge when CS is low.
4
CS
Logic Input Signal. The chip select signal is used to enable the serial port of the AD7817. This is necessary if the AD7817
is sharing the serial bus with more than one device.
5 AGND Analog Ground. Ground reference for track-and-hold comparator and capacitor DAC.
6 REF
IN
Analog Input. An external 2.5 V reference can be connected to the AD7817 at this pin. To enable the on-chip reference,
tie the REF
IN
pin to AGND. If an external reference is connected to the AD7817, the internal reference shuts down.
7
to
10
V
IN1
to V
IN4
Analog Input Channels. The AD7817 has four analog input channels. The input channels are single-ended with respect
to AGND (analog ground). The input channels can convert voltage signals in the range 0 V to V
REF
. A channel is selected
by writing to the address register of the AD7817. See the Control Byte section.
11 V
DD
Positive Supply Voltage, 2.7 V to 5.5 V.
12 DGND Digital Ground. Ground reference for digital circuitry.
13 D
OUT
Logic Output with a High Impedance State. Data is clocked out of the AD7817 serial port at this pin. This output goes
into a high impedance state on the falling edge of RD/WR
or on the rising edge of the CS signal, whichever occurs first.
14 D
IN
Logic Input. Data is clocked into the AD7817 at this pin.
15 SCLK
Clock Input for the Serial Port. The serial clock is used to clock data into and out of the AD7817. Data is clocked out on
the falling edge and clocked in on the rising edge.
16
RD/WR
Logic Input Signal. The read/write signal is used to indicate to the AD7817 whether the data transfer operation is a read
or a write. Set the RD/WR
logic high for a read operation and logic low for a write operation.
