Datasheet

AD7678
Rev. A | Page 10 of 28
Pin No. Mnemonic Type
1
Description
34 PD DI
Power-Down Input. When set to a logic HIGH, power consumption is reduced and conversions are
inhibited after the current one is completed.
35
CNVST
DI
Start Conversion. If CNVST is held HIGH when the acquisition phase (t
8
) is complete, the next falling
edge on CNVST
puts the internal sample/hold into the hold state and initiates a conversion. If CNVST
is held LOW when the acquisition phase is complete, the internal sample/hold is put into the hold
state and a conversion is started immediately.
36 AGND P Must Be Tied to Analog Ground.
37 REF AI
Reference Input Voltage and Internal Reference Buffer Output. Apply an external reference on this pin
if the internal reference buffer is not used. Should be decoupled effectively with or without the
internal buffer.
38 REFGND AI Reference Input Analog Ground.
39 IN– AI Differential Negative Analog Input.
43 IN+ AI Differential Positive Analog Input.
46 REFBUFIN AI
Reference Buffer Input Voltage. The internal reference buffer has a fixed gain. It outputs 4.096 V
typically when 2.5 V is applied on this pin.
48 PDBUF DI
Allows Choice of Buffering Reference. When LOW, buffer is selected. When HIGH, buffer is switched
off.
49
(EPAD)
Exposed Pad
(EPAD)
The exposed pad is internally connected to AGND. This connection is not required to meet the
electrical performances; however, for increased reliability of the solder joints, it is recommended that
the pad be soldered to the analog ground of the system.
1
AI = Analog Input; AO = Analog Output; DI = Digital Input; DI/O = Bidirectional Digital; DO = Digital Output; P = Power.
Table 7. Data Bus Interface Definitions
MODE MODE1 MODE0 D0/OB/
2C
D1/A0 D2/A1 D[3] D[4:9] D[10:11] D[12:15] D[16:17] Description
0 0 0 R[0] R[1] R[2] R[3] R[4:9] R[10:11] R[12:15] R[16:17] 18-Bit Parallel
1 0 1
OB/2C
A0:0 R[2] R[3] R[4:9] R[10:11] R[12:15] R[16:17] 16-Bit High Word
1 0 1
OB/2C
A0:1 R[0] R[1] All Zeros 16-Bit Low Word
2 1 0
OB/2C
A0:0 A1:0 All Hi-Z R[10:11] R[12:15] R[16:17] 8-Bit HIGH Byte
2 1 0
OB/2C
A0:0 A1:1 All Hi-Z R[2:3] R[4:7] R[8:9] 8-Bit MID Byte
2 1 0
OB/2C
A0:1 A1:0 All Hi-Z R[0:1] All Zeros 8-Bit LOW Byte
2 1 0
OB/2C
A0:1 A1:1 All Hi-Z All Zeros R[0:1] 8-Bit LOW Byte
3 1 1
OB/2C
All Hi-Z Serial Interface Serial Interface
R[0:17] is the 18-bit ADC value stored in its output register.