XRD98L56 Datasheet, PDF(29/35 Page) Exar Corporation – CCD Image Digitizers with CDS, PGA and 10-Bit A/D

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XRD98L56 Datasheet, PDF (29/35 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 10-Bit A/D

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XRD9855/9856

XRD98L55/98L56

Digital Output Power Supplies

The DVDD and DGND pins supply power to the digital

output drivers for pins DB[9:0], UNDER, and OVER.

DVDD is isolated from VDD so it can be at a voltage

level less than or equal to VDD. This allows the digital

outputs to interface with advanced digital ASICs requir-

ing reduced supply voltages. For example VDD can be

5.0 or 3.3V, while DVDD is 2.5V.

Power Supply Sequencing

There are no power supply sequencing issues if DVDD

and VDD of the XRD9855/XRD9856 are driven from the

same supply. When DVDD and VDD are driven

separately, VDD must come up at the same time or

before DVDD, and go down at the same time or after

DVDD. If the power supply sequencing in this case is

not followed, then damage may occur to the product due

to current flow through the source-body junction diodes

between DVDD and VDD. An external diode (5082-

2235) layed out close to the converter from DVDD to

VDD prevents damage from occurring when power is

cycled incorrectly.

Note: VDD must be greater than or equal to DVDD or the

source-body diodes will be forward based.

VDD

Output

DVDD

Source-Body

Junction Diode

Between DVDD

& VDD

Digital Output

Source-Body

Junction Diode

Between

DGND & GND

GND

DGND

Figure 24. DVDD & DGND Digital Output Power Supplies,

VDD > DVDD

Rev. 1.01

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