TPS65217: Questions about AC pin and SYS pin connections in case of no battery and no USB.

Hi Kazuya,

Kazuya Nakai59 said:

Q1. They don't use USB and battery. In the case, are connections to AC pin (No.10) and SYS pin(No.6,7) needed?
       They want to connect an external 5V power supply to  VIN_DCDC1~3 and VIN_LDO directly without AC pin and SYS pin connections. Is it no problem?
       Or is it problem because VSYS is internal circuit power supply pin and VSYS can not be opened?

If you don't plan to use the BAT or USB pins, there are a couple issues I see with leaving the AC and SYS pins unused:

a) As you mentioned, there is an internal, always-on power rail that uses the same supply as the SYS pins. If you do not use the AC, USB, BAT, or SYS pins then the internal power rail will not have a source. Certain pins (like the PWR_EN pin) need this internal power rail as a pull up source. I would highly recommend using the AC pin as your power input for this reason.

b) Without using the AC pin, you lose the 20V overvoltage protection of the PMIC. Connecting the source voltage directly to the VIN_DCDCx pins bypasses the internal protection circuitry.

c) The nWAKEUP event that begins the PMIC power cycle is triggered by:

• Rising edge of AC pin voltage OR
• Rising edge of USB pin voltage OR
• Falling edge of PB pin voltage

If you do not have AC or USB, then you will be left with the PB signal as your main option to trigger nWAKEUP. Once nWAKEUP is triggered you can start the full power up sequence by pulling PWR_EN high within 5 seconds of nWAKEUP going low. A similar situation applies to the SLEEP state, but the PWR_EN signal can be used to exit the SLEEP state as an alternative to the PB, so this situation is less restricted.

See the state diagram in Section 8.4 of the datasheet.

Kazuya Nakai59 said:

Q2. Are figure 61 and figure 62 on page 77 of TPS65217 datasheet (SLVSB64I) only solution for the customer case?

We have an application note on VIN brownout that I would highly recommend you look at if you are not planning to use the BAT pins for your design.

In particular, I suggest looking at Section 3.2: Solution Circuit Number 2 for Case A (No Battery)

You can use this application note in addition to the TPS65217x Schematic Checklist to build a stable system.

Kazuya Nakai59 said:

Q3. They referred the following Beaglebone document for their board drawing.

       https://files.seeedstudio.com/wiki/BeagleBone_Green/resources/BEAGLEBONE_GREEN_V1.pdf

      In the document, SN74LVC1G07DCK(U16) which connected to TPS65217 PGOOD pin (No.26) is used.

      What is the reason of U16 using? Is it for signal buffering? Or is it for level shifting? 

U16 is a single 1.65-V to 5.5-V buffer with open-drain outputs. You can look at the part here: SN74LVC1G07

The buffer feeds the NRESET_INOUT pin of the AM335x processor. A high input to the buffer puts the device in a high-z state, so the NRESET_INOUT pin is held high. If the PGOOD signal is de-asserted and pulled low, the buffer will connect its output to GND and pull NRESET_INOUT low causing the processor to respond accordingly to the reset condition.

Regards,

James

Hi Kazuya,

The SN74LVC1G07DCK(U16) is not necessary to pull the 1.8V VIO up to 3.3V. The PWRONRSTn pin of the AM335 has an input high voltage of 1.35V, so 1.8V should be enough for the system to respond correctly.

Regards,

James

Hi Kazuya,

Kazuya Nakai59 said:

Q about Q2. The customer is going to use regulated 5V (VINmax=<5.5V) as TPS65217 power supply. In case of this, can Figure 6. Solution Circuit Number 1 on page 8 of the application note be used? Which is better, Figure 6 or 7?

Figure 6 shows a solution for a VIN =< 5.5V so I would recommend you use that one based on your power supply. Note that you will need to use the push button to wake up the system with this solution.

Kazuya Nakai59 said:

Q1. When VLDO2 pin(No.1) is not used, is it OK that VLDO2 is connected to VIN_LDO pin (No.2)?

That should be fine. VIN_LDO should be tied to VSYS which is usually higher than any expected LDO2 output voltage.

Kazuya Nakai59 said:

Q2. When nWAKEUP pin(No.13) is not connected to anywhere, is it OK to leave open? Or should the pin be pulled up to SYS pin(No.7,8) via a resistor?

I would follow the schematic checklist and pull the pin up to an always-on 3.3V source even if the pin is unused. There may not be an issue with leaving it open but this is not the recommended configuration. 

The pull-up supply should be a separate, always-on source. Pulling the pin up to VSYS can work but you would need to make sure that VSYS is at a stable voltage before any of the dependent signals are used.

Kazuya Nakai59 said:

Q3. The checklist says that 22uF capacitor should be used for L1 and L2 filter (DCDC output).
But TPS65217 datasheet and the document "Powering the AM335x with the TPS65217x"
https://www.ti.com/lit/ug/slvu551i/slvu551i.pdf
say that the capacitors are 10uF. Which is correct?

The schematic checklist was more recently revised in April 2020. The datasheet is reliable as well, but I would go with the more recent information in the checklist. Overall, both the 22uF and 10uF versions should be sufficient for proper device operation.

Kazuya Nakai59 said:

Q4. Do LS1_IN pin (No.39) and LS2_IN(No.42) not need any capacitor? Because the check list don't describe about the capacitor.

If the checklist does not specify a capacitance to be added, you do not need to place a capacitor on this pin. The block diagram in the datasheet (page 18) also shows that LS1_IN and LS2_IN do not have capacitors.

Kazuya Nakai59 said:

Q5. When nRESET pin(No.44) is not used (the device shut down is not needed), is it OK to leave open because the pin is pulled up internally? Or should the pin be pulled up to AC pin(No.10) via a resistor?

nRESET is pulled up internally as you mentioned. You can leave this pin floating if you do not plan to connect it to an external host.

Regards,

James

Hi Kazuya,

You may use solution circuit number 2 (Figure 7) without issues. This one is better if you want to avoid the push-button wakeup.

Regards,

James