LT8722: About abnormal operation by SWEN, SPIS_DAC and instability.

Hi Tomohiro-sama,

Could you please show the schematic of the external circuit in your application that is driving the SWEN-pin?

Yoroshiku,

heke

Hi Heke-san,

Arigato-gozaimasu.

I send schematic to you.

In this case, SPI is input through level converter.

Just now, I only have this schematic.

If you need more information, please tell me how about detail as concrete.

Best Regards,

Tomohiro

Konbanwa Tomohiro-san,

Thank you for the schematics.

Please recheck your circuit at the SFB pin. I think it should not be ac-coupled (C74). Connect SFB directly to the L1 and then C74 to ground.

Yoroshiku onegaishimasu.

heke

Hi Heke-san,

Customer modified circuit to correct connection but the condition of SD and Fault were not changed.

If you have any advice, please tell me it.

Best Regards,

Tomohiro

Hi Tomohiro-san,

OK. Kindly provide the new circuit schematics.

Also, please explain what kind of power supply is used and the type of the TEC.

Yoroshiku, heke

Hi Heke-san,

Sorry for my late reply.

I confirmed about power supply and TEC.

The power supply is

  VDDIO: +3.3V, LT1129CST-3.3

  VIN: +5.5V, i3A4W008A033V-001-R (by TDK Lambda)

And

TEC is below.

PDF

The new schematic is below.

Yoroshiku Onegaishimasu.

Tomohiro

Konnichiwa Tomohiro-san,

Thank you for the additional information.

OK, so just to clarify, your customer is getting fault when changing the SPIS_DAC value during switching operation. Is that correct? Assumingly the value before the change is 0x00000000. What is the new value they are setting the DAC to?

Yoroshiku, heke

Konnichiwa Heke-san,

Now, I confirm to the eval board DC3145A(LT8722) using DC2026C(Linduino).

I try to change register 04 during operation, so I found LT8722 will be stopped if change value is large.

And in the case, change value is small, so LT8722 can change register 04 without shut down.

However, I found also, the output voltage will be changed same time if I change register 04 value.

My confirming condition/environment is using electronic load so I cannot try to change register 04 from positive side to negative side.

Of course, I try to positive to negative changing, LT8722 is shut down.

Coudl you tell me the limit of changing value for register 04 in operation?

Yoroshiku Onegaishimasu.

Tomohiro

Konnichiwa Tomohiro-san,

Thank you for your explanation. 

Do I get it right that you are using an electronic load instead of TEC? That may be the main reason for the problems. The first thing I would try is to replace the electronic load with 1 ohm power resistor (20 watts or so) to see if the operation returns to normal. It is important that both terminals of the load are floating, i.e. not grounded on system level (your electronic load may not be floating). 

Yoroshiku onegaishimasu,

heke

P.S: Send me a message if you'd like to take this off-line. I can build you a TEC controller using LT8722 that works, in a week or so.

Arigatou gozaimasu, Heke-san,

I understood.

I will prepare the power resistor and contact to you again.

Yoroshiku onegaishimasu.

Tomohiro