Texas Instruments TIDA-00204, Manual

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Gigabit
PHY rails
2v5: LMZ10501
1v1: TPS72011
5 V
Enable
signal
Gigabit
PHY I/O rail
3v3: TPS73733
Enable
signal
System Overview
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28 JAJU324B – March 2015 – Revised July 2017
TIDU832
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2.3.1.3.2 Power Supply for Two Gigabit Ethernet PHYs
The PHY power supplies need to provide three power rails. The 3.3-V V
DDIO
power rail is sequenced from
the 3.3-V PMIC rail (see 2.3.1.3.2.1 ). When the V
DDIO
power rail is enabled, it will enable the remaining
two rails 2.5 V and 1.1 V as seen in
図
14 . The information on the power consumption of the Gigabit
Ethernet PHY can be seen in Section 6.5 of the DP83867IR data sheet [1] .
図 図
14. Power Stage for Two Gigabit Ethernet PHYs
2.3.1.3.2.1 DP83867IR Current Consumption
The DP83867IR has two power options. One option requires two rails for the core and one rail for the
V
DDIO
. In this setup, the PHY draws 565 mW. For the two-rail option, no sequencing is required. If power
dissipation on the DP83867IR is critical, the second option uses three rails for core and one rail for V
DDIO
.
In this setup, the PHY draws 545 mW. V
DDIO
can be 3.3, 2.5, or 1.8 V. See its data sheet for more details
on the current consumption per rail and if a voltage other than 3.3 V is used in the V
DDIO
rail [1] .
表 表
14. Power Consumption per Voltage Rail
RAIL STANDARD POWER MODE (565 mW) LOW POWER MODE (545 mW)
1.1 V 106 mA 106 mA
1.8 V N/A 64 mA
2.5 V 157 mA 103 mA
V
DDIO
(3.3, 2.5, or 1.8 V) 31 mA (1.8 V) 31 mA (1.8 V)
For this design, the power supply was designed for the two-rail standard power mode option to fit two
DP83867IR PHYs.
The TPS72011 and LMZ105001 were chosen for the 1.1-V rail and the 2.5-V rail, respectively.
For the V
DDIO
3.3 V, the TPS73733 was chosen. This rail is also used as supply rail for other interfaces on
board (for example, for the Gigabit Ethernet PHY LEDs and V
DDIO
voltage rail, the EEPROM, the debug or
JTAG circuitry, reset circuitry, and additional pull up resistors for data communication lines).
These parts were chosen because of their feature of industrial temperature range –40°C to 85°C and that
they could dissipate the needed power at 85°C. Here it is important to choose the correct package of the
device; several other part numbers could fit the electrical specification. However, their package would not
be able to dissipate the needed power at the full current and temperature range. Knowing the voltage drop
across the LDO and the power dissipation at 85°C, the maximum current that can be dissipated for the
decided voltage rail can be calculated.