TPS23758: Questions about transformer which can be used for TPS23758.

Hi Kazuya,

Q1.
LDT1018-50R is used on TPS23758EVM-080.
They are looking for alternative transformer which has same internal connection as LDT1018-50R.
Do you know any transformer part number?

750318525 from Wurth can be used as alternate part. 

Q2. 
They are evaluating TPS23758 with HA3802-BL.
https://www.coilcraft.com/getmedia/4cce1705-a356-485c-ab91-cc4c65acc6e0/ha380x.pdf
Can this transformer be used with TPS23758?

VCC needs to be higher than 8.6 V. Neglecting the diodes and other voltage drops, this needs SEC:BIAS < 5 V :8.6 V. HA3802-BL can meet this requirements marginally. It should work theoretically. 

Q3. TPS23758 becomes very hot when TPS23758 works with HA3802-BL.
       The secondary side voltage is 5V. This output voltage is come out as expected.
       Do you have any idea of the cause? 

Could you give a temperature for this IC? Is it also hot with LDT1018-50R?

Best regards,

Diang

Hi Diang,

Thank you very much for your reply.

TPS23758 became about 100 degree C when the device works with HA3802-BL.
The device temperature was about 45 degree C  when the device works with LDT1018-50R.

Thank you again and best regards,
Kazuya.

Hi Diang,

Thank you very much for your supports.
The followings are additional information. They don't want to disclose their schematic on E2E.
However the followings are connections between TPS23758 and HA3802-BL.

HA3802-BL     TPS23758         
                1  ->  CP(No.2 pin)
                2  ->  VCC(No.21) via resistor and diode
                3  ->  DRAIN(No.24)
                4  ->  open
                5  ->  PoE(48V) input
                6  ->  open
                7  ->  CSD17579Q3A source (No.1,2,3) and No.11,12 pin of HA3802-BL
                8  ->  CSD17579Q3A gate (No.4) via resistor 
                9  ->  GND (secondary side GND) and No.10 pin of HA3802-BL
              10  ->  GND (secondary side GND) and No.9 pin of HA3802-BL  
              11  ->  CSD17579Q3A source (No.1,2,3) and No.7,12 pin of HA3802-BL
              12  ->  CSD17579Q3A source (No.1,2,3) and No.7,11 pin of HA3802-BL

Is there any wrong connection?

Thank you again and best regards,
Kazuya.

Hi Diang,

I'm sorry I forgot to tell you about VCC pin voltage.
They checked VCC voltage with oscilloscope and it was about 11V constantly.

Thank you and best regards,
Kazuya. 

Hi Kazuya,

Thanks for your additional information.

From your description, I did not think the connection with transformer has issues.

- VCC ~ 11V is higher than I expect. Considering the HA3802-BL has 0.25 : 0.44 SEC : bias. This should give ~8.8-V VCC when Vout is 5 V. Is the Vout = 5V correct when using HA3802-BL? 

- Another thing the customer may miss is a 6.2-V Zener diode is needed on the VB pin.

Best regards,

Diang

Hi Diang,

Thank you very much for your strong support.

The connection between the transformer and TPS23758 which you drew is same as the customer schematic.
Also they place 6.2V Zener diode (MMSZ5234A) between VB and GND(RTN).

Is there anything else as the cause of IC heating?

Thank you again and best regards,
Kazuya.

Hi Kazuya,

A full schematic may be helpful. I can reach out to you via email if you can share the schematic there. 

Best regards,

Diang