[FAQ] TPS65094: Use of ATX Power Supply

Yes, though implementation may vary system to system and a small boost is typically required.

ATX power supply has +12V, +5V, and +3.3V outputs. They are commonly used for desktop computers.

If the 12V is not disabled except during G3, then no modification is necessary, the PMIC should be connected to the 12V and 5V the same as if the 12V was the 2S/3S/4S battery. In particular, the PMIC VSYS pin (pin 55) as well as the input to the three controllers, BUCK1 (VNN), BUCK2 (VCCGI), and BUCK6 (VDDQ).

However, if the 12V shuts down during sleep, then a workaround is needed to prevent the PMIC as interpreting this as a UVLO event and shutting down the system to protect the battery. The PMIC VSYS pin, pin 55, needs to be disconnected from the 12V line and supplied by a signal which will stay above 5.4 V (UVLO) as long as the system is in a state higher than G3. The PMIC VSYS pin does not require much current, typically around 1 mA during normal operation, however the supply will need to be able to handle the inrush current when turning on LDO5 which can be around 300 mA for ~40 us. Common choices for this are the LM2767 voltage doubler, the LM2665 voltage doubler, or the TPS61252 boost converter; though there are plenty of other options.

Finally, the input to the controllers should be considered. BUCK2 (VCCGI) should be connected to the 12V supply, it is only enabled during S0 state so 12V should be enabled. BUCK1 (VNN) is the first rail to turn on during G3 to S5 transition and will need to be powered from the 5V rail. Finally, BUCK6 (VDDQ) is enabled during S4 to S3 transition. If the 12V supply is available when VDDQ would be enabled, then it can be used to power BUCK6. If not, the 5V supply will need to be used. The mismatch between VSYS (pin 55) and controller FET input voltages will result in a slight change of frequency. Some examples are shown below:
•VSYS = 12V and BUCK6 FET Input = 12V --> Fsw = 1 MHz (for the default TPS650941 spin)
•VSYS = 12V and BUCK6 FET Input = 5V --> Fsw = 1.7 MHz (for the default TPS650941 spin)
•VSYS = 12V and BUCK1 FET Input = 12V --> Fsw = 0.9 MHz (for the default TPS650941 spin)
•VSYS = 5.8V and BUCK1 FET Input = 12V --> Fsw = 0.7 MHz (for the default TPS650941 spin)
•VSYS = 5.8V and BUCK1 FET Input = 5V --> Fsw = 1.1 MHz (for the default TPS650941 spin)

One last item is to ensure that VSYS pin (pin 55) is never more than a volt below the V5ANA pin (pin 57). Many boosts use a diode between input and output which should be sufficient to prevent this from happening; otherwise one may need to be added.