Urgently Need help on UCC28710 for USB 5V/2.4A app

Is this a TI reference design that you have a question about?

The UCC28700 is part of a family of products, of which the UCC28710 is another member. Both parts are suitable for a 10W or 12W power supply.

Thanks John for the reply. Yes we're talking about the TI ref design. We're trying to build a 12.5W  5V, 2.5A USB charger using the same IC. Can we use the 'Renco transformers- RTLI-1061 or 1067'  for this design of 12.5W load using the same flyback topology as this ref design?? 

I have a 'Q" about the below sec side of the flyback  topology using UCC28710. We've used the below sch for the sec side in the past. Now I'd like to remove the 2 ICs  TPS2514 & TPS2556 as crossed below to save cost. Sd the circuit not work if I directly connect the + of C2 to the V+ terminal of the USB port as I have shown below? Unfortunately I dont see the open circuit 5V at the V+ & Gnd of the USB channel after removing those 2 ICs. But in your ref design 5V/2A you have not used any of those ICs but the circuit still works.

In my case I found the diode D1 getting damaged each time I remove those ICs & hook the output direct.

Can you please suggest what am I doing wrong here?

Really appreciate your feedback. Thanks in advance, Ari

Ari,

There is a PMP8477 (120Vac 5V 2A) reference design that uses transformer RLTI-1072 and a PMP8363 (120Vac/230Vac 5V 2A) reference design. I cannot find a RTLI-1061 or RTLI-1067 part.

The schematic you attach looks like the secondary of the PMP8363 which uses the RLTI-1067 transformer. This reference design uses flying leads on the secondary leadouts. Are you sure that the leads are connected properly and that the schematic matches what you have actually built? Or are you using the RLTI-1072 transformer on the PMP8363 design ?

There is a note on the PMP8477 schematic that the polarity is wrong on the pcb board. This means that if you are using the PMP8477 circuit board then you will need to reverse the secondary connections. The schematic is correct so you should wire up the pcb as in the PMP8477 schematic.

John Griffin

Thanks John for your reply. Pls note that the design I inherited is the ref design PMP8363 which uses RTLI_1067. Leads in my circuit seem to be correct as the circuit (with U1 & U2 in the secondary) which I sent you previously works fine. I'm not using xfr 1072.

The sec side of TI design looks like below which has no U1 or U2 as shown in the fig which I sent in the previous message. I am wondering if I remove those U1 & U2 which I have crossed in the earlier fig the circuit still does not work. I connected C2(+) directly to V+ of the USB port after removing U1 & U2 which is the same situation as in TI ref design PMP8363. Therefore, I expect to see +5V across C2 but it shows no voltage! Any suggestion is appreciated. Pls let me know if I was able to explain the prob I'm facing or will rephrase it.

I'm also facing thermal challenge while redigning PMP8363 for 12W (5V, 2,4A )instead of current 10W

Thanks again,

Ari

Di you connect C2 (+) to pin 1 of the USB connector and connect C2 (-) to pin 4 of the USB connector?

If you did then you should measure whatever voltage is across C2 also between pins 1 and 4.

 

Thanks John for all the quick responses. Now, I'm modifying PMP8363 design to use the same IC for 12W(5V, 2.4A). I therefore, tried to change the transformer from RLTI-1067(435uH-primary, designed for 11W app) by using RLTI-1083(370uH-primary, designed for 20W app) instead after adjusting the bias & secondary pin connections properly. But I'm not seeing any output voltage in the secondary side. 

Do you see the need for a change in the current limit for this IC if I go ahead with RLTI-1083? If so which resistors from PMP8363 should be readjusted in order to achieve secondary output? 

The main issue I'm facing is with the thermal performance of the transformer for my usb sled application where there is no ventilation and I would like to do thermal management without adding much of a cost to it when going to 2.4A (12W) design from this current design of 2A(10W) this is the reason I'm going with higher power density transformer.

Any tip from your end in this regard will be greatly appreciated.

Thanks in advance,

Ari

You will need to change the values of R5,R8 to match those of the reference design that used the RLTI-1083. This will set the output voltage and turn on voltage. Then you will need to decrease the value of R4,R100 to meet the extra output current.