Hi, TI team,
I am using TPS65218D0 for AM437x.
I am trying to use the TPS6521855 due to the TPS65218D0 shortage problem.
1. TPS65218D0 DCDC4 default : 3.3V
2. TPS6521855 DCDC4 default : 2.5V
Even though I set DC34_SEL(17pin) to 20k, TPS6521855 DCDC4 does outputs 2.3~2.9V.
Even if the resisttor value is changed, 3.3V output does not work.
The attached file is a circuit diagram.
Please advise.
Best Regards,
HJ SOON
Hi HJ,
Table 7-2 in Section 7.3.1.10 of the TPS6521855 datasheet is actually based on the parent device, TPS65218D0. Each variant of the TPS65218xx family will have its own default settings. The 20k resistor setting will program DCDC4 to its default voltage, which is actually 2.5V for the TPS6521855 variant. You can see this 2.5V default mentioned on the first page of the datasheet in the features list.
If you want to change this default from 2.5V to 3.3V, you will need to reprogram the DCDC4 register 0x19 using I2C communication. The TPS6521855 must be in the ACTIVE state for I2C communication to be continuously available. For more instruction on the programming process, take a look at the TPS6521815 datasheet and look at the programming instructions in Section 8.5. The TPS6521855 is not usually meant to be reprogrammed but the method for the TPS6521815 should still work.
This section will describe the flow chart for programming new power up defaults and will also explain the password protection functionality.
Regards,
James
Hi James
First, thank you for reply.
AM437X cannot boot normally due to DCDC4 voltage in some of 200 PCBs. So I can't set I2C.
If it is normal, I am changing to 3.3V in u-boot & kernel.
Normal Boot : DCDC4 -> 2.9V (It is strange why not 2.5V but 2.9V)
Not Boot : DCDC4 -> 2.3~2.5V
So, before setting I2C, I try to adjust the dcdc4 voltage to 3.3V.
Is the TPS6521855 not able to adjust the voltage with the RSEL resistor value?
Regards,
HJ SOON
Hi HJ,
DCDC4 should be able to respond to the RSEL setting but it will not have a 3.3V option. Looking at the table you included in your last post, the spots under DCDC4 where it says 3.3V will actually be 2.5V according to the default setting of the TPS6521855 specifically. To check this I would try some of the higher resistor values to see if you can successfully set DCDC4 to 1.2V or 1.35V. This would indicate that the device is at least working as expected.
There is no way to access I2C without the rails turning on. The TPS6521855 is specifically designed for certain settings and defaults which is why we don't usually recommend trying to replace it with other versions that have different NVM mapping.
If you are already switching devices, I would consider trying the TPS6521815 which is our user programmable version of this PMIC family. This device will allow for custom VOUT settings on the power rails. You could simply copy the register settings from the TPS65218D0 and the TPS6521815 would function in the same manner. It looks like we are currently out of stock but I would highly recommend you go to the TPS6521815 product page and select "notify me when available" next to the part number listing at the bottom of the page.
Regards,
James
