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Miscellaneous Functional Description

PMM Faults

Watchdog Timer

TPS23841

SLUS745A – NOVEMBER 2006 – REVISED MAY 2007

POWER MANAGEMENT MODE FUNCTIONAL DESCRIPTION (continued)

PMM faults are the same as those shown in the AM Faults and INTB Output section. In PM mode, the port

under- and over voltage and under-current faults can be enabled or disabled by writing to the control bits in the

appropriate register. For the TPS23841, port under- and overvoltage detection is disabled by default after device

POR or other reset operation. Under current detection, (DC Disconnect), is enabled by default. The enable state

of these features can be toggled by writing to the corresponding control bit as defined in Table 5 andTable 6 .

The PMM faults are:

• Port under- and over-voltage faults (enable/disable via Common Control register 0001b, bit D2)

• Overcurrent fault (cannot be disabled)

• Under-current (DC Disconnect) fault (enable/disable via Port Control register 0010b, bit D4)

• Thermal shutdown (TSD) fault (cannot be disabled)

• Watchdog fault (disable via WD_DIS pin)

Any one of these faults causes the port to shutdown. Once a fault has occurred the port can not be repowered

until a Disable function is sent. The Disable function clears the fault latch and the fault register.

INTB pin operation is essentially the same in PMM as in AM, with the following exceptions:

• For load under-current to generate a fault shutdown and status indication, the condition of load current less

than the threshold must be detected by the continuous sample (C_SAMPLE) function (0111b).

• In PMM only, a Watchdog timer fault also asserts INTB.

TPS23841 has two watchdog timers. One monitors the I

C clock and the other monitors the internal clock. When

automode is selected and the watchdog timer has not been disabled only the internal clock is monitored. When

in power management mode and the watchdog timer has not been disabled then both the I

C and internal

clocks are monitored. If there is no I

C clock activity for approximately two seconds then all ports are disabled.

There are three means to enable ports after a I

C clock fault and they are:

1. Hard power reset

2. PORB pulse

3. Writing a software reset to the Common Control register.

In both auto mode and power management mode if the internal oscillator is lost for more than 20 ms all ports

are disabled.

Loss of these signals is considered catastrophic since the system loses its ability to talk to each port. Therefore

the watchdog timers disabling all ports protects the system.

This function can be easily over ridden by setting the WD_DIS pin high.

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