TPS3510,TPS3511

PC POWER SUPPLY SUPERVISORS

SLVS312A – JULY 2000 – REVISED DECEMBER 2002

5

POST OFFICE BOX 655303

detailed description

power good and power good delay

A PC power supply is commonly designed to provide a power-good signal, which is defined by the computer

manufacturers. PGO is a power-good signal and should be asserted high by the PC power supply to indicate

that the 5-V and 3.3-V outputs are above the under-voltage threshold limit. At this time the converter should be

able to provide enough power to ensure continuous operation within the specification. Conversely, when either

the 5-V or the 3.3-V output voltages fall below the under-voltage threshold, or when ac power has been removed

for a time sufficiently long so that power supply operation is no longer ensured, PGO should be de-asserted to

a low state.

Figure 1 represents the timing characteristics of the power good (PGO), dc enable (PSON), and the 5 V/3.3 V

supply rails.

t2

t3

t5

t4

5-V/3.3-V

Output

PSON

PGO

On

Off

75%

10%

Figure 1. Timing of PSON and PGO

Although there is no requirement to meet specific timing parameters, the following signal timings are

recommended:

2 ms

≤ t2 ≤ 20 ms, 100 ms < t3 < 2000 ms, t4 > 1 ms, t5 ≤ 10 ms

Furthermore motherboards should be designed to comply with the previously recommended timing. If timings

other than these are implemented or required, this information should be clearly specified.

The TPS3510/1 family of power-supply supervisors provides a power-good output (PGO) for the 3.3-V and 5-V

supply voltage rails and a separate power-good input (PGI). An internal timer is used to generate a power-good

delay. If the voltage signals at PGI, VS33, and VS5 rise above the under-voltage threshold, the open-drain

power-good output (PGO) goes high after a delay of 150 ms or 300 ms. When the PGI voltage or either the 3.3-V

and 5-V power rails drops below the under-voltage threshold, PGO is disabled immediately (after 150-

µs

debounce).

power supply remote on/off (PSON) and fault protect output (FPO)

Since the latest personal computer generation focuses on easy turnon and power saving functions, the PC

power supply requires two characteristics. One is a dc power supply remote on/off function, the other is standby

voltage to achieve very low power consumption of the PC system. Thus the main power needs to be shut down.

The power supply remote on/off (PSON) is an active low signal that turns on all of the main power rails including

3.3 V, 5 V, –5 V, 12 V, and –12 V power rails. When this signal is held high by the PC motherboard or left open

circuited, the signal of the fault protect output (FPO) also goes high. Thus, the main power rails should not deliver

current and should be held at 0 V.