Datasheet

AD7985
Rev. A | Page 7 of 28
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
PIN 1
INDICATOR
1REF
2REF
3REFGND
4REFGND
5IN–
13 CNV
14 SDI
15 TURBO
12 SCK
11 DVDD
6IN+
7PDREF
8VIO
10DGND
9SDO
18
AGND
19
BVDD
20
REFIN
17
AGND
16
AVDD
TOP VIEW
(Not to Scale)
AD7985
NOTES
1. THE EXPOSED PAD IS NOT CONNECTED
INTERNALLY. FOR INCREASED
RELIABILITY OF THE SOLDER JOINTS, IT
IS RECOMMENDED THAT THE PAD BE
SOLDERED TO THE SYSTEM
GROUND PLANE.
07947-004
Figure 4. Pin Configuration
Table 6. Pin Function Descriptions
Pin No. Mnemonic Type
1
Description
1, 2 REF AI Reference Output/Input Voltage.
When PDREF is low, the internal reference and buffer are enabled, producing 4.096 V on this pin.
When PDREF is high, the internal reference and buffer are disabled, allowing an externally supplied
voltage reference up to 5.0 V.
Decoupling is required with or without the internal reference and buffer. This pin is referred to the
REFGND pins and should be decoupled closely to the REFGND pins with a 10 µF capacitor.
3, 4 REFGND AI Reference Input Analog Ground.
5 IN− AI Analog Input Ground Sense. Connect this pin to the analog ground plane or to a remote ground sense.
6 IN+ AI Analog Input. This pin is referred to IN −. The voltage range, that is, the difference between IN+ and IN−,
is 0 V to V
REF
.
7 PDREF DI Internal Reference Power-Down Input. When this pin is low, the internal reference is enabled. When this
pin is high, the internal reference is powered down and an external reference must be used.
8 VIO P Input/Output Interface Digital Power. Nominally at the same supply voltage as the host interface
(1.8 V, 2.5 V, or 2.7 V).
9 SDO DO Serial Data Output. The conversion result is output on this pin. It is synchronized to SCK.
10 DGND P Digital Power Ground.
11 DVDD P Digital Power. Nominally at 2.5 V.
12 SCK DI Serial Data Clock Input. When the part is selected, the conversion result is shifted out by this clock.
13 CNV DI Convert Input. This input has multiple functions. On its leading edge, it initiates the conversions
and selects the interface mode of the part: chain mode or
CS
mode. In
CS
mode, the SDO pin is
enabled when CNV is low. In chain mode, the data should be read when CNV is high.
14 SDI DI Serial Data Input. This input has multiple functions. It selects the interface mode of the ADC as follows.
Chain mode is selected if SDI is low during the CNV rising edge. In chain mode, SDI is used as a data
input to daisy-
chain the conversion results of two or more ADCs onto a single SDO line. The digital data
level on SDI is output on SDO with a delay of 16 SCK cycles.
CS
mode is selected if SDI is high during the CNV rising edge. In
CS
mode, either SDI or CNV can enable
the serial output signals when low. If SDI or CNV is low when the conversion is complete, the busy
indicator feature is enabled.
15 TURBO DI Conversion Mode Selection. When TURBO is high, the maximum throughput (2.5 MSPS) is achieved,
and the ADC does not power down between conversions. When TURBO is low, the maximum throughput
is lower (2.0 MSPS), and the ADC powers down between conversions.
16 AVDD P Input Analog Power. Nominally at 2.5 V.
17, 18 AGND P Analog Power Ground.