AD9640SLASHPCB datasheet(23/41 Pages) AD

23 / 41 page

Preliminary Technical Data

AD9640

Rev. PrD | Page 23 of 41

Gray code when using the SPI control.

Table 3. CLK/DFS Mode Selection (external pin mode)

Voltage at pin

SCLK/DFS

SDIO/DCS

AGND (default)

Binary

DCS Disabled

AVDD

Twos Complement

DCS Enabled

Digital Output Enable Function (OEB)

The AD9640 has a flexible three-state ability for the digital

output pins. The three-state mode can be enabled using the

OEB pin or through the SPI interface. If the OEB pin is low, the

output data drivers are enabled. If the OEB pin is high, the

output data drivers are placed in a high impedance state. It is

not intended for rapid access to the data bus. Note that OEB is

referenced to the digital supplies (DRVDD) and should not

exceed that supply voltage.

Figure 21. OR Relation to Input Voltage and Output Data

TIMING

The AD9640 provides latched data with a pipeline delay of

twelve clock cycles. Data outputs are available one propagation

delay (tPD) after the rising edge of the clock signal.

When using the SPI interface each channel’s data and fast detect

outputs can be independently three-stated by using the Output

Enable Bar bit in register 0x14.

The length of the output data lines and loads placed on them

should be minimized to reduce transients within the AD9640.

These transients can degrade the converter’s dynamic performance.

The AD9640 also provides data clock output (DCO) intended for

capturing the data in an external register. The data outputs are

valid on the rising edge of DCO. See Figure x for a graphical

timing description.

The lowest typical conversion rate of the AD9640 is 10 MSPS.

At clock rates below 10 MSPS, dynamic performance can

degrade.

Table 4. Output Data Format

Input (V)

Condition (V)

Binary Output Mode

Twos Complement Mode

VIN+ – VIN–

< –VREF – 0.5 LSB

00 0000 0000 0000

10 0000 0000 0000

VIN+ – VIN–

= –VREF

00 0000 0000 0000

10 0000 0000 0000

VIN+ – VIN–

= 0

10 0000 0000 0000

00 0000 0000 0000

VIN+ – VIN–

= +VREF – 1.0 LSB

11 1111 1111 1111

01 1111 1111 1111

VIN+ – VIN–

> +VREF – 0.5 LSB

11 1111 1111 1111

01 1111 1111 1111

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