TPS25751: TPS25751 BQ25798 dead battery function

Hi Karl, 

Can you provide a block diagram or schematic of your design along with the TPS25751 JSON configuration? 

Thanks and Regards,

Raymond Lin

USB_PDX_2_2.pdf

Hi Raymond,

here the schematic of the PD part. The liquid detection circuit is disconnected at the moment. 

One furhter question which came up today: I found that the INT output of the BQ25798 is low when the part is in idle mode (no charging or discharging) and high when charged, i.e. in idle it pulls about 300uA through the 10k resistor (which his too much). How can this be avoided or is it possible to disconnect this connection to the TPS25751?

Best regards

Karl

Hi Karl, 

Reviewing the schematic you provided, will provide feedback on the TPS25751 portion. Do you have the JSON for TPS25751 or is that not created yet? 

Schroedinger Karl said:

One furhter question which came up today: I found that the INT output of the BQ25798 is low when the part is in idle mode (no charging or discharging) and high when charged, i.e. in idle it pulls about 300uA through the 10k resistor (which his too much). How can this be avoided or is it possible to disconnect this connection to the TPS25751?

You do not need to connect BQ25798 INT to TPS25751. 

Thanks and Regards,

Raymond Lin

PDX_0_8_1.rar

Hi Raimond, 

here the JSON file. 

Best regards

Karl

Hi Karl, 

Schroedinger Karl said:

The VIN_3V3 is about 2.7V, also the LDO_3V3 (it should be powered from VBUS in that case and be at 3.3V?).

During this scenario, is the system powered on through the battery or through the Type-C connection with a source? If TPS25751 VIN_3V3 is not at a stable 3.3V (2.7V as you described), it may put the PD in an abnormal state of not being able to boot-up. It looks like the VIN_3V3 source is from UBAT0 connected to BAT of BQ25792, is that correct? 

Schroedinger Karl said:

In the data sheet BQ I saw a lower batttery limit of 5V. Does it mean dead battery charging does not work below 5V?

I'll loop in the BQ team for further support on this query. From TPS25751 perspective, the PD can powered on either through VIN_3V3 (3.3V) or its VBUS pin. If TPS25751 is first booted from VBUS, the PD internal power topology will use VBUS as the primary power source until the dead battery flag is cleared. See screenshot from TPS25751 datasheet below: 

Thanks and Regards,
Raymond Lin

Hi Karl,

With VBUS>VBUSUVLO ~=3.4V, the charger enters 100mA trickle charge if the voltage at BATP <=2.5V.  Then starts precharge current until the battery is above VBATLOWV, when it switches to fast charge.  

Regards,

Jeff

Thanks Raimond, Jeff, 

Your question above; the VIN_3V3 is comming from the uC supply which is normaly 3.3V, but in sleep mode it may drop down to 2V depending on the battery status (uC  (MSP430F) works with this voltage). I will try to generate a stable 3.3V for TPS25751 from VBUS and came back later if I have further results. 

Regarding the second answer above: do I need to clear the dead battery flag or ist done automatically? When is a boot necessary, i.e. when is the TPS25751 memory lost?

Regarding Jeffs answer: I did not see any current, also not the 100mA.

I will came back after I did further tests. 

Best regards

Karl 

Hi Raimond, 

in the meantime I modified the power supply. I had to switch off VIN_3V3 and the 5V because the power comsumption is too high (in the mA range). 

Everything is o.k. when I connect a mains charger to  charge the battery. It starts up in dead battery mode (supply from VBUS) and charges my battery. 

But the problem is now that when I connect the (to be charged) smartphone the TPS25751. It goes to dead battery mode (as there is no internal power) and sink mode and cannot charge the smartphone (it discharges the smartphone). I tried to reset (successfully, 00000000 in the register) the dead battery bit but it doesn't work, it does not change the TPS to source mode. 

The procedure is the following: the part is in sleep mode and and VIN_3V3 and 5V  is witched off. Then I connect the smartphone which makes the TPS going to sink mode (and dead battery mode, probably also a reboot from EPROM). Then I switch on the power supply of the TPS (VIN_3V3 and 5V after some seconds) and send a DBfg command. --> Nothing happens.  

1. question: do I need to have a total reset and new reboot?  

2. Can I prevent the TPS25751 from starting a sink or source mode during my sleep mode? i.e. avoiding the dead battery mode? 

Best regards

Karl

Hi Raimond, 

Thanks. 

To your first answer: It is clear that the boot with VBUS only will raise the dead bat flag. But I don't know whether a source or sink is connected when booting from VBUS. In my example (dual power role)  the Port always switches to sink mode (of TPS25751) when booted from VBUS*. If an external source (e.g. mains charger request a sink) is connected and I swap  to source as proposed  will there be conflict or what happens then or will it stay at sink mode? Or happen this: "but failed to complete per the PD spec."? How can the "time out" then be recognized? And the correct command? Do I have to check certain bits? And after this command 'SWSr' is the TPS still in the dual power role or switched to source only mode?

Unfortunately I cannot see which external part is connected (sink or source) because the smartphone (should be sink) acts as a source. If the TPS goes to sink with the smartphone (ext source) and I reconnect physically the USB connector it will automatically switch to source (ext. sink). So the best for me seems to be to reconnect the USB interface somehow. But is this possible electronically e.g. by a certain command? I tried also "DBfg" followed by  "Gaid" command, but it don't work either. 

Above  answers I think are also valid for your second proposal. 

Best regards

Karl

*) If I connect the USB when VIN3V3 and 5V is active, the TPS swiches to the correct behavior (sink with ext. source, source with ext sink). 

Hi Karl, 

Let me check on this and get back to  you early next week. 

Thanks and Regards,

Raymond Lin