ADN8102ACPZ-R7 datasheet(27/36 Pages) AD

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ADN8102

Rev. C | Page 27 of 36

APPLICATIONS INFORMATION

OUTPUT COMPLIANCE

In low voltage applications, users must pay careful attention

to both the differential and common-mode signal levels. The

choice of output voltage swing, preemphasis setting, supply

voltages (VCC and VTTO), and output coupling (ac or dc) affect

peak and settled single-ended voltage swings and the common-

mode shift measured across the output termination resistors.

These choices also affect output current and, consequently,

power consumption. For ac-coupled applications, certain

combinations of supply voltage, output voltage swing, and

preemphasis settings may violate the single-ended absolute output

low voltage, as specified in Table 1. Under these conditions,

the performance is degraded; therefore, these settings are not

recommended. Table 21 includes annotations that identify these

settings. In dc-coupled applications, the far-end termination

voltage should be equal to VTTO to allow the full list of output

swing and preemphasis settings listed in Table 17.

TxHeadroom

The TxHeadroom register (Register 0x23) allows configuration

of the individual transmitters for extra headroom at the output

for high current applications. The bits in this register are active

high (default) and are one per output (see Table 22). Setting a

bit high puts the respective transmitter in a configuration for

extra headroom, and setting a bit low does not provide extra

headroom. The TxHeadroom bits should only be set high when

required for a given output swing as listed in Table 21. Note that

TxHeadroom is not available for VCC < 2.5 V.

VH-DC

VH-PE

VSW-PE

VL-PE

VL-DC

tPE

VTTO

VOCM

VSW-DC

Figure 44. Simplified Output Voltage Levels Diagram

Table 20. Symbol Definitions

Symbol

Formula

Definition

IDC

Programmable

Output current that sets output level

IPE

Programmable

Output current for PE delayed tap

ITTO

IDC + IPE

Total transmitter output current

VDPP-DC

25 Ω × IDC × 2

Peak-to-peak differential voltage swing of

nonpreemphasized waveform

VDPP-PE

25 Ω × ITTO × 2

Peak-to-peak differential voltage swing of preemphasized

waveform

VSW-DC

VDPP-DC/2 = VH-DC – VL-DC

DC single-ended voltage swing

VSW-PE

VDPP-PE/2 = VH-PE – VL-PE

Preemphasized single-ended voltage swing

∆VOCM_DC-COUPLED

25 Ω × ITTO/2

Output common-mode shift, dc-coupled outputs

∆VOCM_AC-COUPLED

50 Ω × ITTO/2

Output common-mode shift, ac-coupled outputs

VOCM

VTTO − ∆VOCM = ( VH-DC + VL-DC )/2

Output common-mode voltage

VH-DC

VTTO − ∆VOCM + VDPP-DC/2

DC single-ended output high voltage

VL-DC

VTTO − ∆VOCM − VDPP-DC/2

DC single-ended output low voltage

VH-PE

VTTO − ∆VOCM + VDPP-PE/2

Maximum single-ended output voltage

VL-PE

VTTO − ∆VOCM − VDPP-PE/2

Minimum single-ended output voltage

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