
Data Sheet
ADN4605
Rev. A | Page 51 of 56
SUPPLY SEQUENCING
Ideally, all power supplies should be brought up to the appropri-
ate levels simultaneously (power supply requirements are set by
the supply limits in
Table 1 and the absolute maximum ratings
brought up separately, the supply power-up sequence is as
follows: DVCC powered first, followed by VCC, and, last the
termination supplies (VTTIA, VTTIB, VTTOA, and VTTOB).
The power-down sequence is reversed with termination
supplies being powered off first. The termination supplies
contain ESD protection diodes to the VCC power domain. To
avoid a sustained high current condition in these devices, the
VTTIx and VTTOx supplies should be powered on after VCC and
should be powered off before VCC.
If the system power supplies have a high impedance in the
powered off state, then supply sequencing is not required
provided the following limits are observed:
Peak current from VTTIxor VTTOx to VCC < 200 mA
Sustained current from VTTIx or VTTOx to VCC < 100 mA
POWER DISSIPATION
voltages, I/O coupling type, and device configuration. The input
termination resistors dissipate power depending on the
differential input swing and common-mode voltage. When ac-
coupled, the common-mode voltage is equal to the termination
supply voltage (VTTIx or VTTOx). While the current drawn from
the input termination supply is effectively zero, there is still
power and heat dissipated in the termination resistors as a result
of the differential signal swing. The core supply current and
output termination current are strongly dependent on device
configuration, such as the number of channels enabled, output
level setting, and output preemphasis setting.
In high ambient temperature operating conditions, it is impor-
tant to avoid exceeding the maximum junction temperature of
the device. Limiting the total power dissipation can be achieved
by the following:
Reducing the output swing
Reducing the preemphasis level
Decreasing the supply voltages within the allowable ranges
Disabling unused channels
Alternatively, the thermal resistance can be reduced by
Adding an external heat sink
Increasing the airflow
section for recommendations for proper thermal stencil layout
and fabrication.
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 VTTOx), 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.
Table 20 shows the change in output common mode (ΔVOCM = VCC VOCM) with output level and preemphasis setting. Single-
ended output levels are calculated for VTTOx supplies of 3.3 V
and 2.5 V to illustrate practical challenges of reducing the
supply voltage. The minimum VL (min VL) cannot be below the
Since the absolute minimum output voltage specified i
n Table 1is relative to VCC, decreasing VCC is required to maintain the
output levels within the specified limits when lower output
termination voltages are required. VTTOx voltages as low as 1.8 V
are allowable for output swings less than or equal to 400 mV
(single-ended).
Figure 53 illustrates an application where the ADN4605 is used
as a dc-coupled level translator to interface a 3.3 V CML driver
to an ASIC with 1.8 V I/Os. The diode in series with VCC
reduces the voltage at VCC for improved output compliance.
TX/XPT HEADROOM
The Tx Headroom and XPT Headroom registers are provided
the core supply voltage (VCC) is greater than 2.7 V. Enabling
the XPT Headroom and Tx Headroom registers allows the
transmitter an extra 300 mV of output compliance. The
headroom circuitry should not be enabled when the core
supply voltage (VCC) is less than or equal to 2.7 V.
When set to 1, the XPT Headroom (Address 0x7D) and Tx
Headroom (Address 0xBB) registers are enabled for all
transmitter outputs. A value of 0 disables the headroom
generating circuitry. Note that both registers (XPT Headroom
and Tx Headroom) must be set for the headroom circuitry to
function properly.