AD7986

Rev. B | Page 7 of 28

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

PIN 1

INDICATOR

1

REF

2

REF

3

REFGND

4

REFGND

5

IN–

13 CNV

14 SDI

15 TURBO

12 SCK

11 DVDD

TOP VIEW

(Not to Scale)

AD7986

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.

Figure 4. Pin Configuration

Table 6. Pin Function Descriptions

Pin No.

Mnemonic

Type1

Description

1, 2

REF

AI

Reference Output/Input Voltage.

When PDREF = low, the internal reference and buffer are enabled, producing 4.096 V on this pin.

When PDREF = 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

Differential Negative Analog Input.

6

IN+

AI

Differential Positive Analog Input.

7

PDREF

DI

Internal Reference Power-Down Input.

When low, the internal reference is enabled.

When 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 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 provides multiple features. It selects the interface mode of the ADC as

follows:

Chain mode is selected if SDI is low during the CNV rising edge. In this 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 18 SCK cycles.

CS mode is selected if SDI is high during the CNV rising edge. In this 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 = high, the maximum throughput (2 MSPS) is achieved. The ADC does not power down

between conversions.

When TURBO = low, the maximum throughput is lower (1.5 MSPS). The ADC powers down between

conversions.