AD6684 datasheet(27/107 Pages) AD

27 / 107 page

Data Sheet

AD6684

Rev. 0 | Page 27 of 107

Treat the clock input as an analog signal in cases where aperture

jitter may affect the dynamic range of the AD6684. Separate the

power supplies for clock drivers from the ADC output driver

supplies to avoid modulating the clock signal with digital noise.

If the clock is generated from another type of source (by gating,

dividing, or other methods), retime the clock by the original clock

at the last step. Refer to the AN-501 Application Note and the

AN-756 Application Note for more in-depth information about

jitter performance as it relates to ADCs.

Figure 66 shows the estimated SNR of the AD6684 across input

frequency for different clock induced jitter values. The SNR can

be estimated by using the following equation:





























 











 

10log

(dBFS)

JITTER

ADC

SNR

Power-Down/Standby Mode

The AD6684 has a PDWN/STBY pin that can be used to

configure the device in power-down or standby mode. The

default operation is power-down. The PDWN/STBY pin is a

logic high pin. When in power-down mode, the JESD204B link

is disrupted. The power-down option can also be set via

In standby mode, the JESD204B link is not disrupted and

transmits zeros for all converter samples. This setting can be

changed using Register 0x0571, Bit 7 to select /K/ characters.

TEMPERATURE DIODE

The AD6684 contains a diode-based temperature sensor for

measuring the temperature of the die. The diode can output a

voltage and serve as a coarse temperature sensor to monitor the

internal die temperature.

The temperature diode voltage can be output to the VCM_CD/

VREF pin using the SPI. Use Register 0x18E6 to enable or disable

the diode. Register 0x18E6 is a local register. Both cores must be

selected in the core index register (Register 0x0009 = 0x03) to

enable the temperature diode readout. It is important to note

that other voltages may be exported to the same pin at the same

time, which may result in undefined behavior. Thus, to ensure a

proper readout, switch off all other voltage exporting circuits as

detailed in this section.

The SPI writes required to export the temperature diode are as

follows (see Table 46 for more information):

Set Register 0x0009 to 0x03 to select both cores.

Set Register 0x18E3 to 0x00 to turn off VCM export.

Set Register 0x18A6 to 0x00 to turn off the voltage

reference.

Set Register 0x18E6 to 0x01 to turn on temperature diode

export. The typical voltage response of the temperature

diode is shown in Figure 67. However, it is recommended

to take measurements from a pair of diodes into account

when introducing another step.

Set Register 0x18E6 to 0x02 to turn on the second

temperature diode (that is, 20× the size) of the pair.

For the method utilizing two diodes simultaneously giving a more

accurate result, see the AN-1432 Application Note, Practical

Thermal Modeling and Measurements in High Power ICs.

0.80

0.75

0.70

0.65

0.60

0.55

0.50

–40

–20

JUNCTION TEMPERATURE (°C)

100

Figure 67. Temperature Diode Voltage vs. Junction Temperature

AD6684 Datasheet(PDF) 27 Page - Analog Devices

AD6684 Datasheet(HTML) 27 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL