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Hello there, I am currently working on an application using the TPS65073 to power an OMAP3530. The application will use a battery that will be charged via USB only. There is no power on/off button, so the device would be required to power up with USB input or by the battery without USB input. However, I would like to clarify operation of the device in two situations, in particular the setting of PB_IN.
The datasheet states that in this type of application when powered from BAT, PB_IN would need to be tied low to enable power up of the converters when POWER_ON is released. For this, I was planning on connecting PB_IN directly to 0V. However, it also states that if the device is powered from USB (and not BAT), PB_IN must not be tied low to start up the converters.
Many Thanks for your input.
Andrew.
Please have a look at page 34 figure 33 of the TPS65073 datasheet.
Figure 33 shows the state diagram of the TPS65073.
There is a difference if the device is powered from
- AC / USB
- BAT
1) In case device is powered from AC/USB
As soon as input voltage is applied to AC or USB the device will transition in POWER_ON (SYS = ON) mode - ramping up the SYS output voltage (output of the Power Path).
The converter remain off in this state. Pulling /PB_IN low or pulling POWER_ON high will cause the DC/DC converters and LDO to ramp with their internal fixed power up seuqence (device transitions in POWER_ON1 state). Please note to keep the converters enabled POWER_ON must be pulled high ,before /PB_IN is released high again. Typ. /PB_IN is connected to an push button, while POWER_ON is controlled by the application processor. If there is no push button (ON/OFF switch in the system) POWER_ON can be directly conneced to SYS - this will cause the converters to start up after AC/USB supply is connected and SYS output voltage ramped up. Note to shut down the converters again in reversed power up seuqence POWER_ON needs to be pulled low again.
2) In case device is supplied from BAT only.
/PB_IN needs to be pulled low. Note that the device needs to detect the falling edge on /PB_IN ==> connecting /PB_IN directly to ground will not work.
When /PB_IN is pulled low SYS output voltage ramps and the DC/DC converters and LDOs ramp up in their internal power up sequence. POWER_ON needs to be pulled high before /PB_IN is released high again to keep the converters enabled.
Please find answers to your questions embedded below.
Pulling /PB_IN static low will not work, since the device needs to detect the falling edge on /PB_IN. Anyway if the device is powered from USB - SYS will ramp up after USB is connected. The converters can be enabled by pulling POWER_ON high. Either control POWER_ON from external circuit of connect POWER_ON to SYS./PB_IN can be left floating (there is an internal pull-up resistor connected to the /PB_IN pin)
2. What set-up would be required to allow the converters to operate from USB when input and BAT otherwise, considering there is no control over PB_IN?
See answer above
Let me know if you have any further questions.
Many Thanks for the response.
It appears that I'd need to leave /PB_IN floating and hook-up VSYS to POWER_ON to meet the requirement.