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AUTO MODE FUNCTIONAL DESCRIPTION

Auto Mode

TPS23841

SLUS745A – NOVEMBER 2006 – REVISED MAY 2007

Auto mode (AM, MS = 0) operation is the basic approach for applying power to IEEE compliant PD’s. When AM

has been selected the TPS23841 automatically performs the following functions:

• Discovery of IEEE 802.3af compliant powered devices (PD's)

• Classification

• Power delivery

• Port over/under voltage detection, (if enabled, see Over/Under Voltage Fault section)

• Port over current detection (570 mA < I

PORT

< 665 mA

• Port maximum current limit (600 mA < I

PORT

< 700 mA)

• DC Disconnect (5 mA < I

PORT

< 10 mA)

• Thermal shutdown protection (TSD), (T

> 150 ° C)

• Internal oscillator watchdog

In AM the contents of all read registers are available via the I

C interface. In addition all control registers except

for the function bits can be written. This supports a semi-auto mode where the TPS23841 auto detects compliant

PD's while a host can access the A/D registers and class information and then implement power management

(including turning a port off, responding to faults, etc).

The write registers that are still active in AM are:

• All ports disable – Common Control register 0001b

• Over/Under Voltage Faults – Common Control register 0001b

• Software reset – Common Control register 0001b

• Disconnect disable – Port Control 1 register 0010b

• Discovery fault disable – Port Control 1 register 0010b

• Port enable – Port Control 2 register 0011b

For alternative B, semi-auto mode implementations which will manipulate the all ports disable or Port Enable

bits, please contact the factory for additional application information.

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