AD2426 datasheet(32/38 Pages) AD

32 / 38 page

Rev. F

Page 32 of 38

November 2023

AD2426/AD2427/AD2428

For a system with all in-line bus powered nodes, IA is calculated

cumulatively from the last in-line node as

IA = IVIN + IB

where:

IA = current that a bus powered subordinate node draws from

an earlier node.

IVIN = current at VIN pin.

IB = B side return current from the next in line node. The next in

line node is the node connected to the B terminal of the current

node.

REDUCING POWER CONSUMPTION

The following sections describe three methods that reduce

power consumption.

Power-Down Mode

Any node in an A2B bus powered system can be shut down by

disconnecting the power supply in the previous subordinate

node (towards the main node). Disconnecting a subordinate

node from the power supply also powers down all of the follow-

ing subordinate nodes (towards the last subordinate node).

Standby Mode

The A2B bus enters standby mode by setting the 

AD242X_DATCTL.STANDBY bit of the main node. The SCF

in standby mode is 19 bits long, instead of 64 bits. In standby

mode, there is no upstream and no downstream traffic on the

A2B bus, and only a minimal SCF keeps all the subordinate

nodes synchronized. This keeps the A2B bus power in the lowest

power state while maintaining clock synchronization between

nodes. Using the equations in the Downstream/Upstream

Activity Level section, the bus activity level in standby mode is,

• Downstream activity level = 19 ÷ 1024 = 1.9%

• Upstream activity level = 0%

The digital transceiver current, including the LVDS TX and RX

current, are subject to the activity levels. The LVDS TX and RX

current also are subject to idle current during the bus idle time.

Control Mode

In control mode, there are no data channels in a superframe.

The superframe only has the 64-bit SCF and SRF in the frame

with the control data embedded in the header bits. Therefore,

the A2B bus power is less when compared to normal mode,

which has data channels in the superframe. Using the equations

in the Downstream/Upstream Activity Level section, the bus

activity level in control mode is,

• Bus activity level downstream = 64 ÷ 1024 = 6.3%

• Bus activity level upstream = 64 ÷ 1024 = 6.3%

The LVDS TX and RX current also are subject to idle current

during the bus idle time.

THERMAL POWER

When calculating power, system designers must consider ther-

mal power. Thermal power calculations are based on the

package thermal characteristics, shown in the following

equation:



JA = thermal resistance

(TJ – TA) ÷ power [°C/W] with airflow = 0 m/s

Table 17 provides the thermal power allowance example. These

values are derived from a JEDEC standard 2S2P test board. JA

values vary significantly and depend on system design and con-

ditions. For the example calculation in Table 17, the JA value

provided is determined using the JEDEC standard conditions.

In this example (Table 17), a subordinate node with 292 mW of

power dissipation is used to provide the maximum estimated

power. The margin is calculated by subtracting the maximum

estimated power from the thermal power allowance.

Table 17. Thermal Power Allowance Example

Parameter

Example Value Unit

105

°C

125

°C

Delta (TJ – TA)20

°C

Example



31.6

°C/W

Maximum Allowed Thermal Power

633

Maximum Estimated Power

292

Power Margin

341

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